As you know,Air compressor is used to increase the air pressure by reducing its volume.Every compressor has to discharge some specific pressure so we can use this utility to operate pneumatic tools etc.Basically electro-pneumatic control is a part of instrument engineering.
To control discharge air pressure of Air Compressor,some controlling devices as like M-type unloader,W-type unloader etc.are used in old days.
The accuracy of such devices are not perfect,to overcome this problem" Electro-Pneumatic control" is introduced.
This is an automatic type capacity control used to replace mechanical unloader.The discharge pressure may be control in 2-step,3-step or 5-step depending upon the model & capacity of the compressor.
It consist of 2 way or 3 way solenoid valves operated by the pressure switches,actuating at receiver pressure.Copper or Nylon tube is used for flow of air from receiver to suction or inlet valve through pressure switch & solenoid valve.
This system also provides the compressor to operate at no-load,till the electric motor attains normal speed & lubricating oil builds up to the required pressure,at the time of initial starting.
At starting of Air Compressor,the air pressure inside the receiver is low so pressure switches energises the solenoid valves.This will stop air supply to inlet or suction valve & compressor comes to full speed,which is known as 100% load.As the receiver pressure increases than the set pressure of pressure switch-1,the contact of switch opens & cut the electric supply of respective solenoid valve & de-energises the same.
Due to this air supply flows to inlet or suction valve and one set of inlet valve open thus compressor unloades partially.i.e. 50% load.If the consumption of compressed air is low than production then air pressure in receiver further increase to the set pressure of another pressure (switch-2) again the contact of switch opens & de-energies the respective solenoid valve.
This unloads the other set of inlet or suction valve & compressor gets fully unloaded which is known as 0% load.
Similarly,fall in receiver pressure causes the pressure switches to energises the solenoid valve & stops air supply to inlet or suction valve & compressor comes on load in steps i.e. 50% load & 100% load.
The pressure switches may be acting direct at receiver pressure or at reduced pressure where process controller is fitted.
As this is modern type of capacity controller,it is essential to take following precautions for smooth operation of capacity control.
01)Keep control filters clean,by draining the moisture collected in the filter bowl.otherwise,this will mix up with dust,oil & other materials and forms paste and restrict the air flow of air or sometimes enter into the inlet valves.
02)Stop air leakage in the impulse line.
03)Do not disturb the setting of pressure switches.
04)Set minimum 0.5 kg/cm square as differential pressure to operate the switch.
05)Use only genuine quality pressure switch & solenoid valves.
Custom Search
Monday
Safety switches used in Air Compressor.
It is very important that the air compressor should run in good working condition to deliver best result,for this we have to take care of this important utility. This is the most important machine in engineering plant.
As I said earlier,we can not keep one operator for full time near to compressor & keep watching performance .That is why it is necessary to provide some safety switches in control panel.This safety devices will work in abnormal condition & stop electric motor and further prevent any breakdown in Air Compressor.
Many safety switches are used to avoid any accident to air compressor.Out of that the most important safety switch is "Low oil pressure switch" in short LOPS. As the name indicates,this switch will operate in condition,when oil pressure in crankcase is lower than set limit & stops the compressor.
The details of LOPS is as below Indfos make IPS-70 switch is commonly used & the function of this switch is to monitor the oil pressure in the crankcase of air compressor.This switch is connected in the oil pressure sensing line coming from the crankcase to the oil pressure gauge,through Tee connection.
The main spring can be set to balance different pressure on the bellows .When the pressure increases,the bellow is affected so that the main spindle is moved upwards until the spring pressure balance the bellow pressure.The spindle has guiding knob and differential adjusting nut which jointly transmit the spindle movement to the switch.
The differential pressure has to be set at zero (Indicator scale at extreme left,facing to LOPS) and the main scale is set to required pressure.(Minimum oil pressure required by the compressor.i.e. 14 PSIG for reciprocating air compressor & 35 PSIG for rotary air compressor).The pressure on main scale can be set by rotating the knob given at top of the switch.
How to set & test Low Oil Pressure Switch.
Connect an Ohmmeter across normal open contact of the switch to observe the switch operation.Start the compressor and watch the oil pressure at which contacts closes,then stop the compressor to see at what oil pressure contacts opens.By adjusting the knob further fine adjustment can be done to the exact pressure required.So confirm the setting by starting & stopping the compressor.
Since the switch remains open during starting,a normal close contact of the timer is connected across the normal open contact of LOPS.The timer is set for 60 sec.As the compressor starts,timer starts its timing cycle and the compressor oil pressure also start building up in 60 sec. timer contacts will becomes open.Due to developed oil pressure in sensing line,LOPS contacts closes & continued the healthy running condition of air compressor.In case the oil pressure does not build due to any reason,this contact remain open and compressor will trip in 60 sec. time span.
A indicator lamp on Solid State Annunciator or any other indication device will flash & hooter starts blowing, rush to compressor immediately & rectify the problem.
As I said earlier,we can not keep one operator for full time near to compressor & keep watching performance .That is why it is necessary to provide some safety switches in control panel.This safety devices will work in abnormal condition & stop electric motor and further prevent any breakdown in Air Compressor.
Many safety switches are used to avoid any accident to air compressor.Out of that the most important safety switch is "Low oil pressure switch" in short LOPS. As the name indicates,this switch will operate in condition,when oil pressure in crankcase is lower than set limit & stops the compressor.
The details of LOPS is as below Indfos make IPS-70 switch is commonly used & the function of this switch is to monitor the oil pressure in the crankcase of air compressor.This switch is connected in the oil pressure sensing line coming from the crankcase to the oil pressure gauge,through Tee connection.
The main spring can be set to balance different pressure on the bellows .When the pressure increases,the bellow is affected so that the main spindle is moved upwards until the spring pressure balance the bellow pressure.The spindle has guiding knob and differential adjusting nut which jointly transmit the spindle movement to the switch.
The differential pressure has to be set at zero (Indicator scale at extreme left,facing to LOPS) and the main scale is set to required pressure.(Minimum oil pressure required by the compressor.i.e. 14 PSIG for reciprocating air compressor & 35 PSIG for rotary air compressor).The pressure on main scale can be set by rotating the knob given at top of the switch.
How to set & test Low Oil Pressure Switch.
Connect an Ohmmeter across normal open contact of the switch to observe the switch operation.Start the compressor and watch the oil pressure at which contacts closes,then stop the compressor to see at what oil pressure contacts opens.By adjusting the knob further fine adjustment can be done to the exact pressure required.So confirm the setting by starting & stopping the compressor.
Since the switch remains open during starting,a normal close contact of the timer is connected across the normal open contact of LOPS.The timer is set for 60 sec.As the compressor starts,timer starts its timing cycle and the compressor oil pressure also start building up in 60 sec. timer contacts will becomes open.Due to developed oil pressure in sensing line,LOPS contacts closes & continued the healthy running condition of air compressor.In case the oil pressure does not build due to any reason,this contact remain open and compressor will trip in 60 sec. time span.
A indicator lamp on Solid State Annunciator or any other indication device will flash & hooter starts blowing, rush to compressor immediately & rectify the problem.
Sunday
High Discharge Air Temperature Switch used for safty of Air Compressor.
It is most important to prevent your Air Compressor from any breakdown,because breakdown not only increase maintenance cost but also suffers your production.You have to bear production loss due to breakdown of machine and engineeering troubles.
Many safety switches as like LOPS,LCWPS,HDATS etc. are installed for safety of compressor.
I have written on LOPS in last post.High Discharge Air Temperature Switch (HDATS) is also one of the most essential safety major has to be taken to prevent any abnormal to your valuable utility.If the temperature of discharge air (i.e.leaving compressed air from high pressure cylinder) is more,than the requirement,it could stuck the piston inside the cylinder,which cause a breakdown of compressor.
A working HDATS will safeguard your compressor from this problem.
A INDFOS Make RT-120 high discharge air temperature switch is normally used for safety of Air Compressor.We will see the details now.This switch having 2 mtr.long capillary connecting the switch and the bulb,with thermowell to fit the bulb.Fit the thermowell in air discharge line in the direction of discharge air flow in angular direction,in between the compressor and AFTER-COOLER,closer to the discharge cylinder.So the discharge air temperature safety can be done.If it has to monitor the air temperature before AFTER-COOLER.Fit the HDATS after the AFTER-COOLER,if it is to monitor the air temperature after AFTER-COOLER.
HDATS has to be set for some high value which is recommended by manufacturer that is why it is essential to set the temperature switch outside in an oil bath,having steady required temperature at the switch to be set.keep the differential setting at zero ,connect an Ohm meter across Normal close (NC)contact of the switch.Immerse the bulb and thermometer in the oil bath,keep stirring.
Set the high Discharge Air Temperature Switch at 170 degree Centigrade,on the main scale.control the steady temperature 170 degree Centigrade of oil bath,now close contact of switch should change & the Ohm meter pointer should show infinity,if not,reduce the setting till the contact changes to open.Increase the temperature setting if the contact opened before 170 degree Centigrade till it closes and opens.Now the switch is set at 170 degree Centigrade.
Confirm the setting once again by heating oil bath after the oil attains the ambient temperature or take fresh oil & continue the process.
After setting the switch,install near the thermowell,fill compressor oil in the thermowell and insert the bulb of temperature switch slowly.Wire the control cable in control pannel to Normal Close (NC) Contact of the switch.
Your Air compressor is more safe if you provide more safety devices.It is not possible to install all the safety due to cost or technical problem but still I recommend to install Low Oil Pressure Switch,Low water Pressure Switch,High Discharge Temperature Switch & Motor Overload Relay.
This four safety switches are most essential to run your Air Compressor without trouble.
Many safety switches as like LOPS,LCWPS,HDATS etc. are installed for safety of compressor.
I have written on LOPS in last post.High Discharge Air Temperature Switch (HDATS) is also one of the most essential safety major has to be taken to prevent any abnormal to your valuable utility.If the temperature of discharge air (i.e.leaving compressed air from high pressure cylinder) is more,than the requirement,it could stuck the piston inside the cylinder,which cause a breakdown of compressor.
A working HDATS will safeguard your compressor from this problem.
A INDFOS Make RT-120 high discharge air temperature switch is normally used for safety of Air Compressor.We will see the details now.This switch having 2 mtr.long capillary connecting the switch and the bulb,with thermowell to fit the bulb.Fit the thermowell in air discharge line in the direction of discharge air flow in angular direction,in between the compressor and AFTER-COOLER,closer to the discharge cylinder.So the discharge air temperature safety can be done.If it has to monitor the air temperature before AFTER-COOLER.Fit the HDATS after the AFTER-COOLER,if it is to monitor the air temperature after AFTER-COOLER.
HDATS has to be set for some high value which is recommended by manufacturer that is why it is essential to set the temperature switch outside in an oil bath,having steady required temperature at the switch to be set.keep the differential setting at zero ,connect an Ohm meter across Normal close (NC)contact of the switch.Immerse the bulb and thermometer in the oil bath,keep stirring.
Set the high Discharge Air Temperature Switch at 170 degree Centigrade,on the main scale.control the steady temperature 170 degree Centigrade of oil bath,now close contact of switch should change & the Ohm meter pointer should show infinity,if not,reduce the setting till the contact changes to open.Increase the temperature setting if the contact opened before 170 degree Centigrade till it closes and opens.Now the switch is set at 170 degree Centigrade.
Confirm the setting once again by heating oil bath after the oil attains the ambient temperature or take fresh oil & continue the process.
After setting the switch,install near the thermowell,fill compressor oil in the thermowell and insert the bulb of temperature switch slowly.Wire the control cable in control pannel to Normal Close (NC) Contact of the switch.
Your Air compressor is more safe if you provide more safety devices.It is not possible to install all the safety due to cost or technical problem but still I recommend to install Low Oil Pressure Switch,Low water Pressure Switch,High Discharge Temperature Switch & Motor Overload Relay.
This four safety switches are most essential to run your Air Compressor without trouble.
Saturday
Details about Solenoid Valve used in Air Compressor.
Solenoid valve is integral part of Electro-Pneumatic Control system of engineering.This valve will control the supply of air to inlet or suction valve in load/unload operation of reciprocating air compressor .
Different types of solenoid valves are available in market.In Air Compressor Technology Normally open (N/O) or Normally Close (N/C) type solenoid valve are used to perform loading/unloading action.
Solenoid valve has three ports,these are
(1) inlet
(2) outlet
(3) exhaust.
use of each port is as below
01)Inlet Port:-Impulse air supply through tube of Dia. not less than 12 mm from the air receiver through control filter connected to inlet port of solenoid valve
02)Outlet Port:-This port is also known as cylinder port.This is connected through,at least 6 mm Dia. Copper or Nylon tube to inlet (Suction) valve of the compressor.
03)Exhaust Port:-This port is for the escape of trapped air in the line.It should always kept open to the atmosphere.
Details of Normal Open & Normal Close Solenoid Valve.
A)Normal Open (N/O):-This type solenoid valve allow air supply to flow from inlet port to outlet (cylinder ) port,in de-energised or normal condition.When energised,due to change over in pressure switch contact stops the air supply.This type of solenoid valve are used for load/unload operation of air compressor.
B)Normal Close (N/C):-This type of solenoid valve does not allow air supply from inlet port to outlet port in de-energised or normal condition.When energised due to change over in contact of pressure switch allows air supply to flow through cylinder port.This type of solenoid valve is used in 5-step control panel for increasing and decreasing the area of clearance pocket during unloading/loading operation of Air Compressor.
Precautions to take for best performance .
01)For perfect functioning of the solenoid valve,always have an air filter,installed in the air line connected to solenoid valve.
02)Always see if the nut tightening the solenoid coil is intact.If loose,tighten the top nut.
Different types of solenoid valves are available in market.In Air Compressor Technology Normally open (N/O) or Normally Close (N/C) type solenoid valve are used to perform loading/unloading action.
Solenoid valve has three ports,these are
(1) inlet
(2) outlet
(3) exhaust.
use of each port is as below
01)Inlet Port:-Impulse air supply through tube of Dia. not less than 12 mm from the air receiver through control filter connected to inlet port of solenoid valve
02)Outlet Port:-This port is also known as cylinder port.This is connected through,at least 6 mm Dia. Copper or Nylon tube to inlet (Suction) valve of the compressor.
03)Exhaust Port:-This port is for the escape of trapped air in the line.It should always kept open to the atmosphere.
Details of Normal Open & Normal Close Solenoid Valve.
A)Normal Open (N/O):-This type solenoid valve allow air supply to flow from inlet port to outlet (cylinder ) port,in de-energised or normal condition.When energised,due to change over in pressure switch contact stops the air supply.This type of solenoid valve are used for load/unload operation of air compressor.
B)Normal Close (N/C):-This type of solenoid valve does not allow air supply from inlet port to outlet port in de-energised or normal condition.When energised due to change over in contact of pressure switch allows air supply to flow through cylinder port.This type of solenoid valve is used in 5-step control panel for increasing and decreasing the area of clearance pocket during unloading/loading operation of Air Compressor.
Precautions to take for best performance .
01)For perfect functioning of the solenoid valve,always have an air filter,installed in the air line connected to solenoid valve.
02)Always see if the nut tightening the solenoid coil is intact.If loose,tighten the top nut.
Friday
How Electro-magnetic Overload Relay works?
Overload Relays are used to protect Electric Motor from failure due to high current drawn by motor.Electric motor has 33% of it's cost in total Air Compressor unit,so it is our duty to protect Electric Motor from any type of failure.Overload Relays are the only solution to protect motor from high current.
Overload Relays are generally of two types one is "Electro-magnetic" and another is "Thermal".
I have already given details about Thermal Overload Relay in past.In this post,you will find details about "Electro-magnetic Overload Relay" which is somewhat outdated from latest engineering,but still some old Air Compressor units are having these type of Relays.
The Electro-magnetic Overload Relays consist of a coil or solenoid carrying the line current (or a portion of it through current transformers) with an armature which when attracted sufficiently operates the release circuit or latch.
A time lag feature is in corporated to guard against unnecessary operation from temporary Overloads due to the normal operation of the machines which are being driven.Time lag is obtained by means of Dash pot (otherwise the action would be practically instantaneous) fitted to the Oil Circuit Breaker (OCB) controlling the stator circuits.
Construction and Adjustment of Dash pot.
The time lag consist of BODY CASTING,MOVABLE PLUNGER,OIL RETAINING SCREW CUP.The movable plunger comprises the core of the Overload release,to which is fitted a specially shaped brass disc moving in a restriction in the body casting,by turning the screw cap the position of the disc within the restriction is varied.
The time lag are dispatched dry and must filled with special time lag oil (SAE-60 grade) provided in separate containers in the Circuit Breaker.While fitting remove screw "A".It is not necessary to remove the bottom cup "B" and on no account should screw "C" be removed.
Adjustment of the Overload setting is made by slackening screw "D" and sliding the body casting up or down,until the top face coincides with the calibration marking required on the calibration tube,screw "D' is then tightened.The bottom rotatable cup "B" is now described reset themselves after operation within few second.
This type of Overload Relays are very simple in operation but due care must taken for accurate operation.All the marks "A","B","C"&"D" are embossed on respective spaces,you have to identify first before working on "Electro-magnetic Overload Relay".
Overload Relays are generally of two types one is "Electro-magnetic" and another is "Thermal".
I have already given details about Thermal Overload Relay in past.In this post,you will find details about "Electro-magnetic Overload Relay" which is somewhat outdated from latest engineering,but still some old Air Compressor units are having these type of Relays.
The Electro-magnetic Overload Relays consist of a coil or solenoid carrying the line current (or a portion of it through current transformers) with an armature which when attracted sufficiently operates the release circuit or latch.
A time lag feature is in corporated to guard against unnecessary operation from temporary Overloads due to the normal operation of the machines which are being driven.Time lag is obtained by means of Dash pot (otherwise the action would be practically instantaneous) fitted to the Oil Circuit Breaker (OCB) controlling the stator circuits.
Construction and Adjustment of Dash pot.
The time lag consist of BODY CASTING,MOVABLE PLUNGER,OIL RETAINING SCREW CUP.The movable plunger comprises the core of the Overload release,to which is fitted a specially shaped brass disc moving in a restriction in the body casting,by turning the screw cap the position of the disc within the restriction is varied.
The time lag are dispatched dry and must filled with special time lag oil (SAE-60 grade) provided in separate containers in the Circuit Breaker.While fitting remove screw "A".It is not necessary to remove the bottom cup "B" and on no account should screw "C" be removed.
Adjustment of the Overload setting is made by slackening screw "D" and sliding the body casting up or down,until the top face coincides with the calibration marking required on the calibration tube,screw "D' is then tightened.The bottom rotatable cup "B" is now described reset themselves after operation within few second.
This type of Overload Relays are very simple in operation but due care must taken for accurate operation.All the marks "A","B","C"&"D" are embossed on respective spaces,you have to identify first before working on "Electro-magnetic Overload Relay".
Thursday
Different Types of Starters Used in Air Compressor.
Air compressor are driven by electric motor and these motors are started by different types of starters according to the requirement.These starters may be fully automatic with push button to operate or totally manual type,as per the design of the manufacturer and the choice of the customer.Here I will write about automatically operated and manually operated starters which are most important part of electrical engineering and air compressor.
01)Automatic Type Starters:-
This consist of contactors with built in coils and plunger.Pressing the starters button energises the operating coil which closes the contactor.In order that the contactor may remain closed when the "Start " push button is released,retaining contactors are required.
These are closed by the contactor lever itself and thus maintain the operating coil circuit,once it has been made and the contactors closed,irrespective of the position of the "Start" push button.Depression of the "Stop" push button or failure of supply to the operating coil immediately comes the contactor to open.
By energising,the operating coil from the same circuit as supplies the motor such an arrangement is equivalent to a no volt release.(Example-Automatic Direct-On-line (DOL) Starter and Automatic Star-Delta Starters are of these type)
02)Manual Operated Starters:-
For safety,all manual operating motor starting switch or circuit breaker return to the "Off" position in the event of failure of the incoming supply,and for this purpose an "Under voltage" or "No volt" release is fitted.The under voltage release forms an inherent part of the starting switch in all electro-magnetically operated starters,but is incorporated to the starting switch.
With drum type AC Starters having a manually operated starting handle,the starting switch is fitted with a spring which biases the switch to the "Off"position,but is retained in the "On" position by a mechanical latch fitted in the starter is a shunt-wound electro-magnet or solenoid excited by the supply voltage.
In the event of supply failure,the plunger or armature of the solenoid or electro-magnet is released and is arranged to knock off the hold-on latch and so return the switch to the "Off" position.
Mostly Star-Delta Starters are used in Air Compressor Technology.
01)Automatic Type Starters:-
This consist of contactors with built in coils and plunger.Pressing the starters button energises the operating coil which closes the contactor.In order that the contactor may remain closed when the "Start " push button is released,retaining contactors are required.
These are closed by the contactor lever itself and thus maintain the operating coil circuit,once it has been made and the contactors closed,irrespective of the position of the "Start" push button.Depression of the "Stop" push button or failure of supply to the operating coil immediately comes the contactor to open.
By energising,the operating coil from the same circuit as supplies the motor such an arrangement is equivalent to a no volt release.(Example-Automatic Direct-On-line (DOL) Starter and Automatic Star-Delta Starters are of these type)
02)Manual Operated Starters:-
For safety,all manual operating motor starting switch or circuit breaker return to the "Off" position in the event of failure of the incoming supply,and for this purpose an "Under voltage" or "No volt" release is fitted.The under voltage release forms an inherent part of the starting switch in all electro-magnetically operated starters,but is incorporated to the starting switch.
With drum type AC Starters having a manually operated starting handle,the starting switch is fitted with a spring which biases the switch to the "Off"position,but is retained in the "On" position by a mechanical latch fitted in the starter is a shunt-wound electro-magnet or solenoid excited by the supply voltage.
In the event of supply failure,the plunger or armature of the solenoid or electro-magnet is released and is arranged to knock off the hold-on latch and so return the switch to the "Off" position.
Mostly Star-Delta Starters are used in Air Compressor Technology.
Wednesday
How to Protect Electric Motor from Failure?
Mostly Air Compressors are driven by electric motor.This is the cheap option available comparing with other options such as diesel generator etc.
The operating cost of any air compressor can be reduced by using electric motor as a driving media.This is true when your electric motor runs very smoothly.But think,if your electric motor failed to start due to burning of motor winding or failure of bearings etc.
What will be the cost of repairing or replacement? This cost may be near about 33% of your Air Compressor cost.Do you believe this? For small engineering units this costs much more in the form of breakdown and production losses.To keep Air Compressor running cost at lower side,we have to protect our electric motor from failure.Most frequently motor failed due to excessive current drawn by motor.
To protect electric motor from excessive current a "Overload Protection Relay" is placed in electric circuit.
Excessive current may be due to either mechanical overload on the motor or due to electrical system,due to unbalance supply voltage or single phasing or defective starter or defective in the motor itself.In either case it is essential that the supply should be disconnected before any damage is done to the motor.An overload device thus usually operates by releasing the latching-in device by disconnecting the supply to no-volt coil or in contactor starters by operating the operating coil circuit.
Overload Relays are generally of two types.
01)Electro-magnetic
02)Thermal Electro-magnetic overload relays are old type which is not in use recent days that's why I am giving details about Thermal Overload relay.
These are mostly used in Air Compressor now a days.
Thermal Overload relay:-
This may be bi-metal strips or solder pot elements and in either case as the action is due to their heating up,a time element is always present.The action of bi-metal strips over load release depends on the movement resulting from the different rates of expansion of the two metals forming the combined strip when heated.
The bi-metal strip may be directly heated by the current or indirectly heated by a coil of resistance wire which carries the current.Thermal Overload relays are usually of the hand reset type,the reset feature is combined with the relay.
How to set Motor Overload Protection Relay.For closer protection of the motor,particularly against single phasing condition, the bi-metal overload relay is connected in the phase circuit.hence relay should be set for 0.6 times the actual line current drawn by the motor,as measured by an ammeter.In the absence of an ammeter the following procedure may be followed.
01)Start the motor with overload relay setting at 0.6 times the rated motor current for star-delta starter and for rest of the starter at motor full load current stamped on the name plate.
02)After the motor reaches the pick load condition,reduce the relay setting gradually till the relay trips.
03)Set the relay slightly higher than the tripping value.
04)To check the setting is correct or not,allow relay to cool down,then restart the motor and make sure,relay does not trip during starting.If trips,increase the relay setting slightly and check again.
05)To check the tripping,increase the unloading air pressure setting of air compressor by 1 kilogram per centimeter square from maximum rated air pressure,when the current increases than the normal peak load current,the relay should trip.(Allow air compressor to run for more than 5 minute from peak pressure condition).If relay don't trip,slightly reduce the setting.
The operating cost of any air compressor can be reduced by using electric motor as a driving media.This is true when your electric motor runs very smoothly.But think,if your electric motor failed to start due to burning of motor winding or failure of bearings etc.
What will be the cost of repairing or replacement? This cost may be near about 33% of your Air Compressor cost.Do you believe this? For small engineering units this costs much more in the form of breakdown and production losses.To keep Air Compressor running cost at lower side,we have to protect our electric motor from failure.Most frequently motor failed due to excessive current drawn by motor.
To protect electric motor from excessive current a "Overload Protection Relay" is placed in electric circuit.
Excessive current may be due to either mechanical overload on the motor or due to electrical system,due to unbalance supply voltage or single phasing or defective starter or defective in the motor itself.In either case it is essential that the supply should be disconnected before any damage is done to the motor.An overload device thus usually operates by releasing the latching-in device by disconnecting the supply to no-volt coil or in contactor starters by operating the operating coil circuit.
Overload Relays are generally of two types.
01)Electro-magnetic
02)Thermal Electro-magnetic overload relays are old type which is not in use recent days that's why I am giving details about Thermal Overload relay.
These are mostly used in Air Compressor now a days.
Thermal Overload relay:-
This may be bi-metal strips or solder pot elements and in either case as the action is due to their heating up,a time element is always present.The action of bi-metal strips over load release depends on the movement resulting from the different rates of expansion of the two metals forming the combined strip when heated.
The bi-metal strip may be directly heated by the current or indirectly heated by a coil of resistance wire which carries the current.Thermal Overload relays are usually of the hand reset type,the reset feature is combined with the relay.
How to set Motor Overload Protection Relay.For closer protection of the motor,particularly against single phasing condition, the bi-metal overload relay is connected in the phase circuit.hence relay should be set for 0.6 times the actual line current drawn by the motor,as measured by an ammeter.In the absence of an ammeter the following procedure may be followed.
01)Start the motor with overload relay setting at 0.6 times the rated motor current for star-delta starter and for rest of the starter at motor full load current stamped on the name plate.
02)After the motor reaches the pick load condition,reduce the relay setting gradually till the relay trips.
03)Set the relay slightly higher than the tripping value.
04)To check the setting is correct or not,allow relay to cool down,then restart the motor and make sure,relay does not trip during starting.If trips,increase the relay setting slightly and check again.
05)To check the tripping,increase the unloading air pressure setting of air compressor by 1 kilogram per centimeter square from maximum rated air pressure,when the current increases than the normal peak load current,the relay should trip.(Allow air compressor to run for more than 5 minute from peak pressure condition).If relay don't trip,slightly reduce the setting.
Tuesday
Pre-Commissioning Checks of Electrical Motor Used to Run Air Compressor.
Air compressor is the utility which consumes maximum electric power in any engineering plant.Air compressor can be driven by the DG Set also,but it is very expensive option comparing to driven by electric motor.maximum plants used electric driven air compressor for compressed air purpose.It is also most important to know about electricals & instrumentations used in air compressor.If you have no knowledge about electricals then it will be very diffcult to run air compressor sometimes.You will get some knowledge from this post,which contains general information about the electricals used with air compressor.
Induction Motor,Squirrel cage or wound rotor (Slipring) type,of various ratings & suitable motor starting gears,are employed according to the capacity of the Air Compressor.These may be of Low Voltage (LV) or High Voltage (HV) grade,depending upon the requirment.
It is most important to install electric motor with proper check-ups.If your electric motor installed properly,then you are rest assured that you will get maximum working life and trouble free operation.Follow below
pre-commissioning checks to get best result from electric motor.
01)Check Name Plate details of electric motor & Starter,both the specification should match each other.It is most important to match Rotor Volts (RV) andRotor Amps (RA) of Slipring Motor.
02)Inspect for any transit damages.If found any damage,report the nature of damage to the nearest office of compressor manufacturer if purchased with Air Compressor or Motor manufacturer if purchased seperately.The delay in reporting the matter would involve considerable problems to claim the damages from insurance authorities or the concerned equipment manufacturers.
03)Perior to installation,the motor should be stored in a clean,dry place.The motor parts have a protective coat of anti-rust preservative which should notbe removed during normal storage period.In case of long storage,periodic examinations should be carried out and fresh preservative applied,if requiredafter any rust or moisture has been removed.
04)Before putting the electric motor into operation,measure the insulation resistance between the motor winding & frame with Megger.A 500 volt meggeris required for low voltage motor.The insulation resistance must above 2 megohms,if found below the value,motor should be "Dried Out".Insulation resistance of Starter should not be less than 20 megohms.
05)If motor is stored for more than 8 months period,then before starting the electric motor ,the bearing cover should be removed and the grease in the bearing cover should be pressed with thumbs between the race of the bearings.If any detorioration of grease is apparant,the old grease should be removed and new grease pressed into the bearings & housing.
Induction Motor,Squirrel cage or wound rotor (Slipring) type,of various ratings & suitable motor starting gears,are employed according to the capacity of the Air Compressor.These may be of Low Voltage (LV) or High Voltage (HV) grade,depending upon the requirment.
It is most important to install electric motor with proper check-ups.If your electric motor installed properly,then you are rest assured that you will get maximum working life and trouble free operation.Follow below
pre-commissioning checks to get best result from electric motor.
01)Check Name Plate details of electric motor & Starter,both the specification should match each other.It is most important to match Rotor Volts (RV) andRotor Amps (RA) of Slipring Motor.
02)Inspect for any transit damages.If found any damage,report the nature of damage to the nearest office of compressor manufacturer if purchased with Air Compressor or Motor manufacturer if purchased seperately.The delay in reporting the matter would involve considerable problems to claim the damages from insurance authorities or the concerned equipment manufacturers.
03)Perior to installation,the motor should be stored in a clean,dry place.The motor parts have a protective coat of anti-rust preservative which should notbe removed during normal storage period.In case of long storage,periodic examinations should be carried out and fresh preservative applied,if requiredafter any rust or moisture has been removed.
04)Before putting the electric motor into operation,measure the insulation resistance between the motor winding & frame with Megger.A 500 volt meggeris required for low voltage motor.The insulation resistance must above 2 megohms,if found below the value,motor should be "Dried Out".Insulation resistance of Starter should not be less than 20 megohms.
05)If motor is stored for more than 8 months period,then before starting the electric motor ,the bearing cover should be removed and the grease in the bearing cover should be pressed with thumbs between the race of the bearings.If any detorioration of grease is apparant,the old grease should be removed and new grease pressed into the bearings & housing.
Monday
Details About Current Meter.
To Measure Average Velocity of Different Methods can be used in hydraulics engineering.Out of that Floats and Pitot Tube is already covered in earlier posts.In this post I will cover "Current Meter" which is used to Measure Average Velocity of Flow.This Average Velocity of Flow is required to Measure the River Discharge
Current Meter:-
It consist of a Wheel containing Blades or Cups which are Rotate by the Flowing Water.A Electric Current is supplied to Wheel by means of Wire.
A Rotation of Wheel makes and breaks the Electric Circuit,which causes an Electric Bell to Ring.The Velocity of Flowing Water is obtained by counting the ringing of the Bell,the Rotation at Wheel.
The Current Meter is suspended by means of a fine cable and lowered to the required Depth.The Current Meter is free to move about its Horizontal and Vertical Axis,so that it can Adjust itself with the Direction of Water Flow.
Rating of Current Meter:-
The process of obtaining the relationship between the number of Electric Signals,Transmitted from Current Meter in unit time,and the Velocity of Flowing Water,Flowing past the Meter is known as the Rating of Current Meter
By Rating Curve or Rating Table,we can Directly obtain the Velocity of Water with the corresponding Signals.
Precautions for Rating of Current Meter:-
01)The Water in the Rating Tank must be allowed to come completely to rest,after each run and beginning of the next.
02)The Current Meter must not be allowed to approach too closely to the sides or bottom of the Rating Channel.
03)The Rating Channel should not be less than 2 meter wide and 1.5 meter Deep.It should be long enough to permit a clear run at a Constant Speed for at least 15 meters.
04)The Current Meter should be supported by the same type of Rod or Cable,which is intended to be used during the Velocity observations in Field.
Current Meter:-
It consist of a Wheel containing Blades or Cups which are Rotate by the Flowing Water.A Electric Current is supplied to Wheel by means of Wire.
A Rotation of Wheel makes and breaks the Electric Circuit,which causes an Electric Bell to Ring.The Velocity of Flowing Water is obtained by counting the ringing of the Bell,the Rotation at Wheel.
The Current Meter is suspended by means of a fine cable and lowered to the required Depth.The Current Meter is free to move about its Horizontal and Vertical Axis,so that it can Adjust itself with the Direction of Water Flow.
Rating of Current Meter:-
The process of obtaining the relationship between the number of Electric Signals,Transmitted from Current Meter in unit time,and the Velocity of Flowing Water,Flowing past the Meter is known as the Rating of Current Meter
By Rating Curve or Rating Table,we can Directly obtain the Velocity of Water with the corresponding Signals.
Precautions for Rating of Current Meter:-
01)The Water in the Rating Tank must be allowed to come completely to rest,after each run and beginning of the next.
02)The Current Meter must not be allowed to approach too closely to the sides or bottom of the Rating Channel.
03)The Rating Channel should not be less than 2 meter wide and 1.5 meter Deep.It should be long enough to permit a clear run at a Constant Speed for at least 15 meters.
04)The Current Meter should be supported by the same type of Rod or Cable,which is intended to be used during the Velocity observations in Field.
Sunday
How You Can Measure The River Discharge?
For various purpose,the Measurement of River Discharge is required.It requires lot of Skill and the Accuracy.To Measure the Discharge of River,we require
01)Area of Flow
02)Average Velocity of Flow.
With this Data we can Calculate
Discharge=Area of Flow X Average Velocity of Flow.
To Calculate Area of Flow,we can use following Methods
A)Simple Segment Method:-
In this Method,the whole Width of River is divided into a number of Segment at Length,say L1,L2,L3 (Length of Segments) and at Depth say d1,d2,d3 (mean Depth of Segment).Now,the Area of Flow is Sum of all Area of Segments.(L1d1+L2d2+L3d3..................)
B)Simpson's Rule:-
In this Method,the whole Width of River is divided into an even number of equal Segments,so that there are odd number of Depths taken at the end of each Segment.
02)Average Velocity of Flow:-
To Measure Average Velocity of Flow following are three important Methods we can use.
A)Floats
B)Pitot Tube
C)Current Meter
Out of that Pitot Tube is already covered in earlier post.In this post I will cover Details about Floats and in next post,you will come to know about Current Meter.
A)Floats:-
With the help of Single Float,the Surface Velocity,at any section of River can be easily obtained.For this we have to count time taken by the Float to Travel known Distance.The Velocity is Calculate by dividing the distance travelled by the Float by the time taken to travel that distance.
This Surface Velocity is then converted into an Average Velocity.To obtain Average Velocity directly,a Double Float or Rod Float is used.
01)Double Float:-
It consist of two Floats connected by a Wire or String.One Float is a Small Wooden Float,which Floats on Surface of River .Another is a Hallow Metallic Sphere which is heavier than Water is suspended from the former by a Wire or String,connecting the two Floats,in such that,the Lower Metallic Float is at Depth of 6/10 of the Total Depth of Flow,as the Average Velocity of Flow exists at a Depth of 6/10 to the Total Depth.
The Velocity of Flow then Calculate by Dividing the distance travelled by the Float by the time taken to travel that distance.This Method Directly gives the Value of Average Velocity.
02)Rod Float:-
It consist of a Wooden Rod or a Metallic Rod Weighted at the bottom,so as to keep it Vertical or Inclined while travelling.
The Length of the Rod is so adjusted that it should not touch the Weeds at bottom of the River and its top should be above the Water Surface.A Telescope Rod may be used to suit different Depths.A section free from Weeds must be chosen to avoid possibilities of the Weeds at the bottom of River to Interface with Rod Float.
01)Area of Flow
02)Average Velocity of Flow.
With this Data we can Calculate
Discharge=Area of Flow X Average Velocity of Flow.
To Calculate Area of Flow,we can use following Methods
A)Simple Segment Method:-
In this Method,the whole Width of River is divided into a number of Segment at Length,say L1,L2,L3 (Length of Segments) and at Depth say d1,d2,d3 (mean Depth of Segment).Now,the Area of Flow is Sum of all Area of Segments.(L1d1+L2d2+L3d3..................)
B)Simpson's Rule:-
In this Method,the whole Width of River is divided into an even number of equal Segments,so that there are odd number of Depths taken at the end of each Segment.
02)Average Velocity of Flow:-
To Measure Average Velocity of Flow following are three important Methods we can use.
A)Floats
B)Pitot Tube
C)Current Meter
Out of that Pitot Tube is already covered in earlier post.In this post I will cover Details about Floats and in next post,you will come to know about Current Meter.
A)Floats:-
With the help of Single Float,the Surface Velocity,at any section of River can be easily obtained.For this we have to count time taken by the Float to Travel known Distance.The Velocity is Calculate by dividing the distance travelled by the Float by the time taken to travel that distance.
This Surface Velocity is then converted into an Average Velocity.To obtain Average Velocity directly,a Double Float or Rod Float is used.
01)Double Float:-
It consist of two Floats connected by a Wire or String.One Float is a Small Wooden Float,which Floats on Surface of River .Another is a Hallow Metallic Sphere which is heavier than Water is suspended from the former by a Wire or String,connecting the two Floats,in such that,the Lower Metallic Float is at Depth of 6/10 of the Total Depth of Flow,as the Average Velocity of Flow exists at a Depth of 6/10 to the Total Depth.
The Velocity of Flow then Calculate by Dividing the distance travelled by the Float by the time taken to travel that distance.This Method Directly gives the Value of Average Velocity.
02)Rod Float:-
It consist of a Wooden Rod or a Metallic Rod Weighted at the bottom,so as to keep it Vertical or Inclined while travelling.
The Length of the Rod is so adjusted that it should not touch the Weeds at bottom of the River and its top should be above the Water Surface.A Telescope Rod may be used to suit different Depths.A section free from Weeds must be chosen to avoid possibilities of the Weeds at the bottom of River to Interface with Rod Float.
Why Surge Tank Is Rquired in Hydro Electric Power Plant?
In Hydro Electric Power Plant Water is used to generate Power by using some Hydraulic Machines.For the smooth operation of Power Plant some necessary arrangements are required,Surge Tank is one of them.
The requirement of Surge Tank is due to some problems which occurred in Water Flow.First I will cover the possible problems in Flowing Water,these are,
A)Water Hammer:-
Due to Motion,Water possess some Momentum.This Momentum is destroyed,if the Flowing water is suddenly brought to rest,by closing the Valve.
A very High Pressure is developed on Valve.This High Pressure is followed by a series of Pressure Vibrations,resulting noise in pipe.This noise is known as "Knocking".
The sudden rise in Pressure has the effect of Hammering Action on the walls of pipe, known as Water Hammer.This Water Hammer can burst the pipe
In Hydro Electric Power Plant,the requirement of Water goes on changing,that's why it is essential to increase or decrease the Discharge flowing through the pipe line.
Whenever the requirement of Water suddenly decreased,the Valve must suddenly closed,resulting a very High Pressure developed in entire pipe line between the Reservoir and the Turbine.This is happened due to Water Hammer.
To overcome this problem,a Storage Reservoir called as "Pen Stock" is fitted at some opening made on the pipe line in order to store Water when the Valve is suddenly closed, or to discharge Water when increased discharged is required.Such a Storage Reservoir is known as "Surge Tank".
Functions of Surge Tank.01)To control the Pressure Variations,due to rapid changes in the pipeline flow,thus eliminating Water Hammer possibilities.
02)To regulate the flow of Water to the Turbine by providing necessary retarding Head of Water.
The Surge Tanks are placed near to the Turbine.The Height of Surge Tank is generally kept above the maximum Water Level in the supply Level Reservoir.
There are three important types of Surge Tanks used in Hydro Electric Power Plant.
01)Simple Surge Tank
02)Restricted Orifice type Surge Tank
03)Differential Surge Tank.
The requirement of Surge Tank is due to some problems which occurred in Water Flow.First I will cover the possible problems in Flowing Water,these are,
A)Water Hammer:-
Due to Motion,Water possess some Momentum.This Momentum is destroyed,if the Flowing water is suddenly brought to rest,by closing the Valve.
A very High Pressure is developed on Valve.This High Pressure is followed by a series of Pressure Vibrations,resulting noise in pipe.This noise is known as "Knocking".
The sudden rise in Pressure has the effect of Hammering Action on the walls of pipe, known as Water Hammer.This Water Hammer can burst the pipe
In Hydro Electric Power Plant,the requirement of Water goes on changing,that's why it is essential to increase or decrease the Discharge flowing through the pipe line.
Whenever the requirement of Water suddenly decreased,the Valve must suddenly closed,resulting a very High Pressure developed in entire pipe line between the Reservoir and the Turbine.This is happened due to Water Hammer.
To overcome this problem,a Storage Reservoir called as "Pen Stock" is fitted at some opening made on the pipe line in order to store Water when the Valve is suddenly closed, or to discharge Water when increased discharged is required.Such a Storage Reservoir is known as "Surge Tank".
Functions of Surge Tank.01)To control the Pressure Variations,due to rapid changes in the pipeline flow,thus eliminating Water Hammer possibilities.
02)To regulate the flow of Water to the Turbine by providing necessary retarding Head of Water.
The Surge Tanks are placed near to the Turbine.The Height of Surge Tank is generally kept above the maximum Water Level in the supply Level Reservoir.
There are three important types of Surge Tanks used in Hydro Electric Power Plant.
01)Simple Surge Tank
02)Restricted Orifice type Surge Tank
03)Differential Surge Tank.
Saturday
Which Are The Important Hydraulic Coefficients Used in Hydraulic Engineering.
Before entering into the details of the Hydraulic Coefficients,following definitions must be clearly understood by an engineering student.This will help you to better understand about following Hydraulic Coefficients.
A)Jet of Water:-
The Continuous Stream of Liquid,that comes out or flows out of an Orifice,is known as "Jet of Water".
B)Vena Contracta:-
When a Tank fitted with an Orifice,the Liquid Particles,in order to Flow out through the Orifice,moves towards the Orifice from all Directions.A few of the particles first moves downward,then take a turn to enter into the Orifice,and then finally Flow through it.
While taking turn to enter into to the Orifice,the Liquid Particles lose some Energy.Due to which,it is observed that the Jet after leaving the Orifice,gets contracted.
The maximum Contraction takes place at a section slightly on the downstream side of a Orifice,where the Jet of Water is more or less Horizontal.Such a section is known as "Vena Contracta"
Now we will see the four important Hydraulic Coefficients.These Coefficients are also known as Orifice Coefficients.
01)Coefficient of Contraction:-
The ratio of Area of the Jet at Vena Contracta,to the Area of the Orifice,is known as "Coefficient of Contraction".Its value will varies slightly with the available Head of the liquid,size and shape of the Orifice.
An Average Value of Coefficient of Contraction is 0.64
02)Coefficient of Velocity:-
The ratio of Actual Velocity of Jet at Vena Contracta,to the Theoretical Velocity is known as "Coefficient of Velocity".The difference occurs between the Velocities due to Friction of the Orifice.
For the Sharp Edge Orifice,the Value of Coefficient of Velocity increases with the Head of Water.
03)Coefficient of Discharge:-
The ratio of a Actual Discharge through an Orifice to the Theoretical Discharge,is known as "Coefficient of Discharge".
The Value of Coefficient of Discharge varies with the Value of Coefficient of Contraction and Coefficient of Velocity.An average is about 0.62
04)Coefficient of Resistance:-
The ratio of Loss of Head in the Orifice to the Head of water available at the exit of the Orifice is known as "Coefficient of Resistance".
The Coefficient of Resistance generally neglected,while solving numerical problems.
A)Jet of Water:-
The Continuous Stream of Liquid,that comes out or flows out of an Orifice,is known as "Jet of Water".
B)Vena Contracta:-
When a Tank fitted with an Orifice,the Liquid Particles,in order to Flow out through the Orifice,moves towards the Orifice from all Directions.A few of the particles first moves downward,then take a turn to enter into the Orifice,and then finally Flow through it.
While taking turn to enter into to the Orifice,the Liquid Particles lose some Energy.Due to which,it is observed that the Jet after leaving the Orifice,gets contracted.
The maximum Contraction takes place at a section slightly on the downstream side of a Orifice,where the Jet of Water is more or less Horizontal.Such a section is known as "Vena Contracta"
Now we will see the four important Hydraulic Coefficients.These Coefficients are also known as Orifice Coefficients.
01)Coefficient of Contraction:-
The ratio of Area of the Jet at Vena Contracta,to the Area of the Orifice,is known as "Coefficient of Contraction".Its value will varies slightly with the available Head of the liquid,size and shape of the Orifice.
An Average Value of Coefficient of Contraction is 0.64
02)Coefficient of Velocity:-
The ratio of Actual Velocity of Jet at Vena Contracta,to the Theoretical Velocity is known as "Coefficient of Velocity".The difference occurs between the Velocities due to Friction of the Orifice.
For the Sharp Edge Orifice,the Value of Coefficient of Velocity increases with the Head of Water.
03)Coefficient of Discharge:-
The ratio of a Actual Discharge through an Orifice to the Theoretical Discharge,is known as "Coefficient of Discharge".
The Value of Coefficient of Discharge varies with the Value of Coefficient of Contraction and Coefficient of Velocity.An average is about 0.62
04)Coefficient of Resistance:-
The ratio of Loss of Head in the Orifice to the Head of water available at the exit of the Orifice is known as "Coefficient of Resistance".
The Coefficient of Resistance generally neglected,while solving numerical problems.
Practicle Application Of Bernoulli's Equation On Hydraulic Devices.
Bernoulli's Equation has widest application in Hydraulics and Applied Hydraulics.It is used for derivation of many Formula.In this post I will cover its Application on the following Hydraulic Devices.
01)Venturimeter:-
The Venturimeter is an apparatus,for finding out the Discharge of a Liquid Flowing through a pipe.
Venturimeter has consist of three parts,
A)Convergent Cone:-
It is the short pipe which converges from Diameter d1 to a smaller Diameter d2.It is also known as "Inlet" of venturimeter.The slope of Converging sides is between 1 in 4 or 1 in 5.
B)Throat:-
It is small portion of circular pipe,in which the Diameter d2 is kept constant.
C)Divergent Cone:-
It is a pipe,which Diverges from Diameter d2 to a large Diameter d1.It is also known as "Outlet" of the Venturimeter.The Length of the Divergent Cone is about 3 to 4 times than that of the Convergent Cone.
02)Orifice Meter:-
This is used to measure the Discharge in a pipe.An Orifice Meter in its simplest form,consist of a Plate having a Sharp Edge circular Hole,known as "Orifice"
This Plate is fixed inside the pipe.The Mercury Manometer is inserted to know the difference of Pressure between the pipe and the Orifice.
03)Pitot Tube:-
It is the instrument to determine the Velocity of Flow at the required point in a pipe or stream.Pitot Tube consist of a glass Tube bent through 90 degree.
The lower end of the Tube faces the direction of Flow.The Liquid rises up in the tube to the Pressure exerted by the Flowing Liquid.By measuring the rise of a Liquid in the Tube,we an find out,the Velocity of the Liquid Flow.
01)Venturimeter:-
The Venturimeter is an apparatus,for finding out the Discharge of a Liquid Flowing through a pipe.
Venturimeter has consist of three parts,
A)Convergent Cone:-
It is the short pipe which converges from Diameter d1 to a smaller Diameter d2.It is also known as "Inlet" of venturimeter.The slope of Converging sides is between 1 in 4 or 1 in 5.
B)Throat:-
It is small portion of circular pipe,in which the Diameter d2 is kept constant.
C)Divergent Cone:-
It is a pipe,which Diverges from Diameter d2 to a large Diameter d1.It is also known as "Outlet" of the Venturimeter.The Length of the Divergent Cone is about 3 to 4 times than that of the Convergent Cone.
02)Orifice Meter:-
This is used to measure the Discharge in a pipe.An Orifice Meter in its simplest form,consist of a Plate having a Sharp Edge circular Hole,known as "Orifice"
This Plate is fixed inside the pipe.The Mercury Manometer is inserted to know the difference of Pressure between the pipe and the Orifice.
03)Pitot Tube:-
It is the instrument to determine the Velocity of Flow at the required point in a pipe or stream.Pitot Tube consist of a glass Tube bent through 90 degree.
The lower end of the Tube faces the direction of Flow.The Liquid rises up in the tube to the Pressure exerted by the Flowing Liquid.By measuring the rise of a Liquid in the Tube,we an find out,the Velocity of the Liquid Flow.
What Is Bernoulli's Equation And Its Limitations.
In Hydrodynamics the Motion of Liquid and the Forces causing Flow are covered.In this post,I will cover some topics of Hydrodynamics.
Energy of a Liquid in Motion.
Energy means the capacity to do work.Mainly three important Energy Forms are possessed by a Liquid,these are as follows.
01)Potential Energy:-
It is the Energy possessed by a Liquid particle,by virtue of its position.
02)Kinetic Energy:-
It is the Energy possessed by a Liquid particle,by virtue of its Motion or Velocity.
03)Pressure Energy:-
It is the Energy possessed by a Liquid particle,by virtue of its existing Pressure.
Bernoulli's Equation:-
It states that "For a perfect Incompressible Liquid,flowing in a continuous Stream,the total Energy of a particle remain the same,while the particle moves from one point to another".There is one assumption that "there are no Friction Losses in Pipe".
Limitation of Bernoulli's Equation:-
01)The Velocity of Liquid particle in the centre of a pipe is maximum and gradually decreases towards the walls of the pipe due to friction.Thus while using Bernoulli's Equation,only the Mean Velocity of the Liquid should be taken into account because the Velocity of Liquid particles is not uniform.As per assumption it is not practical.
02)There are always some external Forces acting on the Liquid,which affects the Flow of Liquid.Thus while using Bernoulli's Equation,all such external forces are neglected which is not happened in actual practise.If some Energy is supplied to or extracted from the Flow,same should also taken into account.
03)In Turbulent Flow some Kinetic Energy is converted into Heat Energy and in a Viscous Flow some Energy is lost due to Shear Forces.Thus while using Bernoulli's Equation all such losses should be neglected,which is not happened in actual practise.
04)If the Liquid is Flowing through curved path,the Energy due to Centrifugal Forces should also be taken into account.
Energy of a Liquid in Motion.
Energy means the capacity to do work.Mainly three important Energy Forms are possessed by a Liquid,these are as follows.
01)Potential Energy:-
It is the Energy possessed by a Liquid particle,by virtue of its position.
02)Kinetic Energy:-
It is the Energy possessed by a Liquid particle,by virtue of its Motion or Velocity.
03)Pressure Energy:-
It is the Energy possessed by a Liquid particle,by virtue of its existing Pressure.
Bernoulli's Equation:-
It states that "For a perfect Incompressible Liquid,flowing in a continuous Stream,the total Energy of a particle remain the same,while the particle moves from one point to another".There is one assumption that "there are no Friction Losses in Pipe".
Limitation of Bernoulli's Equation:-
01)The Velocity of Liquid particle in the centre of a pipe is maximum and gradually decreases towards the walls of the pipe due to friction.Thus while using Bernoulli's Equation,only the Mean Velocity of the Liquid should be taken into account because the Velocity of Liquid particles is not uniform.As per assumption it is not practical.
02)There are always some external Forces acting on the Liquid,which affects the Flow of Liquid.Thus while using Bernoulli's Equation,all such external forces are neglected which is not happened in actual practise.If some Energy is supplied to or extracted from the Flow,same should also taken into account.
03)In Turbulent Flow some Kinetic Energy is converted into Heat Energy and in a Viscous Flow some Energy is lost due to Shear Forces.Thus while using Bernoulli's Equation all such losses should be neglected,which is not happened in actual practise.
04)If the Liquid is Flowing through curved path,the Energy due to Centrifugal Forces should also be taken into account.
Friday
Which Mechanical Gauges Are Used To Measured Fluid Pressure?
A Mechanical gauge is best to measure High Fluid Pressure,where Tube Gauge cannot be conveniently used.The principle on which all Gauges work is almost same.Following three types of Gauges are more important from subject point of view.
01)Bourdon's Tube Pressure Gauge:-
The Bourdon's Tube Pressure Gauge is most suitable to measure the pressure of fluid,above or below the Atmosphere Pressure.In its simplest form,consists of an elliptical tube ABC,bent into an arc of a circle.
This bent-up tube is connected to the fluid at C (inlet of Fluid),the pressurised fluid flows into the tube,as a result of the increased Pressure,tends to straighten itself.
The tube tends to become circular as it is encased in circular cover.With the help of simple Pinion and Sector arrangement,the elastic deformation of the Bourdon's tube rotates the Pointer.This Pointer moves over a Calibrated Scale.Which directly shows the Pressure.
02)Diaphragm Pressure Gauge:-
This Pressure Gauge is also used to found out the Pressure of a Fluid,above or below Atmosphere Pressure.Instead of Bourdon's tube a Corrugated Diaphragm is used,hence it is called Diaphragm Pressure Gauge.
When the Gauge is connected to the Fluid at C(inlet of Fluid), causes some deformation of the Diaphragm due to fluid pressure.With the help of some Pinion arrangement,the elastic deformation of the Diaphragm rotates the Pointer.This Pointer moves over the Calibrated Scale.Which directly shows the Pressure.
A Diaphragm Pressure Gauge is generally,used to measure relatively Low pressure.
03)Dead Weight Pressure Gauge:-
This type of Pressure Gauge is generally used for the Calibration of the other Pressure Gauge in a Laboratory.In its simplest form,consist of a Piston and a Cylinder of known area and connected to a Fluid by a Tube.
A Pressure Gauge,to be Calibrated,is fitted on the other end of the tube.By changing the Weight,on the Piston,the Pressure on the Fluid is calculated and marked on the Pointer.
By taking adequate precaution,a small error due to Frictional Resistance to the Motion of the Piston,an be avoided.
01)Bourdon's Tube Pressure Gauge:-
The Bourdon's Tube Pressure Gauge is most suitable to measure the pressure of fluid,above or below the Atmosphere Pressure.In its simplest form,consists of an elliptical tube ABC,bent into an arc of a circle.
This bent-up tube is connected to the fluid at C (inlet of Fluid),the pressurised fluid flows into the tube,as a result of the increased Pressure,tends to straighten itself.
The tube tends to become circular as it is encased in circular cover.With the help of simple Pinion and Sector arrangement,the elastic deformation of the Bourdon's tube rotates the Pointer.This Pointer moves over a Calibrated Scale.Which directly shows the Pressure.
02)Diaphragm Pressure Gauge:-
This Pressure Gauge is also used to found out the Pressure of a Fluid,above or below Atmosphere Pressure.Instead of Bourdon's tube a Corrugated Diaphragm is used,hence it is called Diaphragm Pressure Gauge.
When the Gauge is connected to the Fluid at C(inlet of Fluid), causes some deformation of the Diaphragm due to fluid pressure.With the help of some Pinion arrangement,the elastic deformation of the Diaphragm rotates the Pointer.This Pointer moves over the Calibrated Scale.Which directly shows the Pressure.
A Diaphragm Pressure Gauge is generally,used to measure relatively Low pressure.
03)Dead Weight Pressure Gauge:-
This type of Pressure Gauge is generally used for the Calibration of the other Pressure Gauge in a Laboratory.In its simplest form,consist of a Piston and a Cylinder of known area and connected to a Fluid by a Tube.
A Pressure Gauge,to be Calibrated,is fitted on the other end of the tube.By changing the Weight,on the Piston,the Pressure on the Fluid is calculated and marked on the Pointer.
By taking adequate precaution,a small error due to Frictional Resistance to the Motion of the Piston,an be avoided.
What Are The Practical Applications Of Hydrostatics.
The Hydrostatics Pressure is either utilised in the working of a Hydraulic Structure,or a Structure is checked to withstand the Hydrostatic Pressure exerted on it.
That's why study of Hydrostatics is more important in engineering .In this post I will cover practical applications of Hydrostatics on the following Structures.
01)Water Pressure on Sluice Gate:-
To regulate the flow of Water,in the path of a River,a Sluice Gate is provided.The Sluice Gate is made to move up and down with the help of Rollers fixed on Skin Plate,which travel on Vertical Rails called Guide.
These Rails are fixed on Piers or Vertical Walls.
In between these two Skin Plates,a number of I-beams are provided horizontally to withstand the Water Presure.The spacing between the I-beam is lesser at the bottom than that at top of Sluice Gate,as the Water Pressure varies in the depth.
02)Water Pressure on Lock Gate:-
The Water Level on both sides of the Dam will be different.If it is desired to have Boating in such river,the Chamber,known as Lock,is constructed between these two different Water Levels.Two sets of Lock Gates are provided in order to transfer a Boat from Higher Water Level to Lower Water Level.
The Upstream gates are opened,and the Water Level in the Chamber is rises up to the Upstream Water level.The Boat is then shifted in the chamber,then Upstream Gates are closed and Downstream Gates are opened and the Water Level in the Chamber is lowered to the Downstream Water level.The procedure is reversed for the transfer of Boat from Downstream to Upstream.
03)Water Pressure on Masonry Walls:-
When Water on one side of Masonry Walls,the Water Pressure will act perpendicular to the Wall.A little consideration will show,that the intensity of Pressure at Water Level will be Zero and will be increase by a Straight Line Law to wH at the bottom.
Thus the Pressure of the Water on a Vertical Wall will act through a point at a distance H/3 from the bottom,where H is the depth of Water.
Conditions for Stability of Dam.
01)The Resultant must pass within the base to safeguard Dam against Overturning.
02)The Resultant must pass through the middle third of the base,to avoid tension at the base.
03)To prevent sliding,the maximum Frictional Force should be more than the Horizontal Force.
04)The Maximum Stress developed at the bottom of the Dam should be within the permissible Stress of the site.
That's why study of Hydrostatics is more important in engineering .In this post I will cover practical applications of Hydrostatics on the following Structures.
01)Water Pressure on Sluice Gate:-
To regulate the flow of Water,in the path of a River,a Sluice Gate is provided.The Sluice Gate is made to move up and down with the help of Rollers fixed on Skin Plate,which travel on Vertical Rails called Guide.
These Rails are fixed on Piers or Vertical Walls.
In between these two Skin Plates,a number of I-beams are provided horizontally to withstand the Water Presure.The spacing between the I-beam is lesser at the bottom than that at top of Sluice Gate,as the Water Pressure varies in the depth.
02)Water Pressure on Lock Gate:-
The Water Level on both sides of the Dam will be different.If it is desired to have Boating in such river,the Chamber,known as Lock,is constructed between these two different Water Levels.Two sets of Lock Gates are provided in order to transfer a Boat from Higher Water Level to Lower Water Level.
The Upstream gates are opened,and the Water Level in the Chamber is rises up to the Upstream Water level.The Boat is then shifted in the chamber,then Upstream Gates are closed and Downstream Gates are opened and the Water Level in the Chamber is lowered to the Downstream Water level.The procedure is reversed for the transfer of Boat from Downstream to Upstream.
03)Water Pressure on Masonry Walls:-
When Water on one side of Masonry Walls,the Water Pressure will act perpendicular to the Wall.A little consideration will show,that the intensity of Pressure at Water Level will be Zero and will be increase by a Straight Line Law to wH at the bottom.
Thus the Pressure of the Water on a Vertical Wall will act through a point at a distance H/3 from the bottom,where H is the depth of Water.
Conditions for Stability of Dam.
01)The Resultant must pass within the base to safeguard Dam against Overturning.
02)The Resultant must pass through the middle third of the base,to avoid tension at the base.
03)To prevent sliding,the maximum Frictional Force should be more than the Horizontal Force.
04)The Maximum Stress developed at the bottom of the Dam should be within the permissible Stress of the site.
Thursday
Some Important Terms About Equilibrium Of Floating Body.
We normally see,whenever a body is placed over a Liquid,either it sinks or floats on the Liquid.
The body placed over the Liquid is subjected to the following two forces.
01)Gravitational force.
02)Upthrust of the Liquid.
These two forces acts opposite to each other.If the Gravitational Force is more than the Upthrust of the Liquid,the Body will sink down,if the Gravitational Force is less than the Upthrust of the Liquid,the Body will float.
This will best understood by the Archimede's Principle.
01)Archimede's Principle:-
It states that "Whenever a body is immersed wholly or partially in a Fluid,it is lifted up by a force equal to a Weight of Fluid Displaced by the Body".
02)Buoyancy:-
The tendency of a Fluid to uplift a submerged body,because of upward thrust of the Fluid,is known as Buoyancy.It is always equal to the Weight of Fluid Displaced by the Body.
If the Force of the Buoyancy is less than the Weight of the Body,it will sink down.When the Force of the Buoyancy is more than the Weight of the Body,it will pushed up till the Weight of the Fluid Displaced is equal to the Weight of the Body.
03)Centre Of Buoyancy:-
It is the point,through which the force of the Buoyancy is supposed to act.It is always the Centre of Gravity of the Volume of the Liquid Displaced.
04)Metacentre:-
Whenever a body,floating in a Liquid,is given a small angular Displacement,it starts Oscillating about some point.This point,about which Body starts Oscillating,is known as "Metacentre".
05)Metacentric Height:-
The distance between the centre of Gravity of a floating Body,and the Metacentre is called "Metacentric Height".More the Metacentric Height of floating Body,more it will be stable.
The body placed over the Liquid is subjected to the following two forces.
01)Gravitational force.
02)Upthrust of the Liquid.
These two forces acts opposite to each other.If the Gravitational Force is more than the Upthrust of the Liquid,the Body will sink down,if the Gravitational Force is less than the Upthrust of the Liquid,the Body will float.
This will best understood by the Archimede's Principle.
01)Archimede's Principle:-
It states that "Whenever a body is immersed wholly or partially in a Fluid,it is lifted up by a force equal to a Weight of Fluid Displaced by the Body".
02)Buoyancy:-
The tendency of a Fluid to uplift a submerged body,because of upward thrust of the Fluid,is known as Buoyancy.It is always equal to the Weight of Fluid Displaced by the Body.
If the Force of the Buoyancy is less than the Weight of the Body,it will sink down.When the Force of the Buoyancy is more than the Weight of the Body,it will pushed up till the Weight of the Fluid Displaced is equal to the Weight of the Body.
03)Centre Of Buoyancy:-
It is the point,through which the force of the Buoyancy is supposed to act.It is always the Centre of Gravity of the Volume of the Liquid Displaced.
04)Metacentre:-
Whenever a body,floating in a Liquid,is given a small angular Displacement,it starts Oscillating about some point.This point,about which Body starts Oscillating,is known as "Metacentre".
05)Metacentric Height:-
The distance between the centre of Gravity of a floating Body,and the Metacentre is called "Metacentric Height".More the Metacentric Height of floating Body,more it will be stable.
How You Can Measure Fluid Pressure?
The Principle of all the Pressure Measuring Devices are almost same,but for our convenient sake,we may divide it into following two types.
01)TUBE GAUGE
02)MECHANICAL GAUGE
In this post I will cover details about Tube Gauges.
Tube Gauges to measure Fluid Pressure.
The Device used to measuring Fluid Pressure,by the Gauges are,
01)Piezometer Tube.
02)Manometer.
Details about Piezometer Tube.
It is the simplest form of Manometer,used for measuring moderate pressure.It consist of a Tube,open at one end to the Atmosphere,in which,Liquid can rise freely without overflow,the Height,to which the Liquid rises up in the Tube,gives the Pressure Head directly.
To find out the Pressure of a Liquid flowing through pipe,a Piezometer Tube is connected to the pipe.The important care to be taken that the Tube should not project inside the pipe beyond the surface,all the burrs and roughness near the hole must be removed and the edge of the hole should be rounded off.
A Piezometer Tube is not suitable for measuring Negative Pressure because Air will enter in the pipe through the Tube.
Details about Manometers.
It is the improved form of a Piezometer Tube.With the help of Manometer,you can measure,High Pressure and Negative Pressure also.
Following are four important types of Manometers.
01)Simple Manometer:-
It is the slightly improved form of Piezometer Tube for measuring High as well as Negative Pressure of Liquid.It consist a tube bent in U-shape,one end of which is attached to the Gauge point and another is open to the Atmosphere.
Generally,Mercury which is 13.6 times heavier than Water is used as Liquid in Simple Manometer.Hence you can measure High Pressure also.
02)Micromanometer:-
It is the modified form of Manometer,in which cross section area of Left Limb is 100 times larger than that of Right Limb.A Micromanometer,is used for measuring Low Pressure,where accuracy is much more important.
These Micromanometer is further divided into two types which are
A)Vertical Tube Micromanometer
B)Inclined Tube Micromanometer
The Inclined Tube Mocromanometer is more sensitive than that of Vertical Tube Micromanometer.
03)Differential Manometer:-
It is the Device used for measuring the difference of Pressures,between two points in a pipe or in two different pipes.
A Differential Manometer,in its simplest form,consists of a U-tube,containing heavy liquid ,whose two ends are connected to the points,whose difference of Pressure is required to be found out.
04)Inverted Differential Manometer:-
It is particular type of Differential Manometer,in which an inverted U-tube is used.It is used for measuring difference of Low Pressures,where accuracy is the prime consideration.
It consists of an Inverted U-Tube,containing a light Liquid whose two ends are connected to the point whose difference of Pressure is to be found out.
01)TUBE GAUGE
02)MECHANICAL GAUGE
In this post I will cover details about Tube Gauges.
Tube Gauges to measure Fluid Pressure.
The Device used to measuring Fluid Pressure,by the Gauges are,
01)Piezometer Tube.
02)Manometer.
Details about Piezometer Tube.
It is the simplest form of Manometer,used for measuring moderate pressure.It consist of a Tube,open at one end to the Atmosphere,in which,Liquid can rise freely without overflow,the Height,to which the Liquid rises up in the Tube,gives the Pressure Head directly.
To find out the Pressure of a Liquid flowing through pipe,a Piezometer Tube is connected to the pipe.The important care to be taken that the Tube should not project inside the pipe beyond the surface,all the burrs and roughness near the hole must be removed and the edge of the hole should be rounded off.
A Piezometer Tube is not suitable for measuring Negative Pressure because Air will enter in the pipe through the Tube.
Details about Manometers.
It is the improved form of a Piezometer Tube.With the help of Manometer,you can measure,High Pressure and Negative Pressure also.
Following are four important types of Manometers.
01)Simple Manometer:-
It is the slightly improved form of Piezometer Tube for measuring High as well as Negative Pressure of Liquid.It consist a tube bent in U-shape,one end of which is attached to the Gauge point and another is open to the Atmosphere.
Generally,Mercury which is 13.6 times heavier than Water is used as Liquid in Simple Manometer.Hence you can measure High Pressure also.
02)Micromanometer:-
It is the modified form of Manometer,in which cross section area of Left Limb is 100 times larger than that of Right Limb.A Micromanometer,is used for measuring Low Pressure,where accuracy is much more important.
These Micromanometer is further divided into two types which are
A)Vertical Tube Micromanometer
B)Inclined Tube Micromanometer
The Inclined Tube Mocromanometer is more sensitive than that of Vertical Tube Micromanometer.
03)Differential Manometer:-
It is the Device used for measuring the difference of Pressures,between two points in a pipe or in two different pipes.
A Differential Manometer,in its simplest form,consists of a U-tube,containing heavy liquid ,whose two ends are connected to the points,whose difference of Pressure is required to be found out.
04)Inverted Differential Manometer:-
It is particular type of Differential Manometer,in which an inverted U-tube is used.It is used for measuring difference of Low Pressures,where accuracy is the prime consideration.
It consists of an Inverted U-Tube,containing a light Liquid whose two ends are connected to the point whose difference of Pressure is to be found out.
Wednesday
3 Important Pressures Of The Fluid.
The Intensity of Pressure at any point in a Fluid is the same in all direction,when it is at rest.
01)Atmospheric Pressure:-
It is established that the Air possesses some Weight and due to its Weight,Air must exert some Pressure on the Surface of the Earth.The Density of Air is different at different heights due to its property of Compressibility.
The Density of Air has also vary from time to time due to change in its Temperature and Humidity.Due to these factors,the Atmospheric Pressure of Air can not be calculated,as is done in case of Liquid.
The Atmospheric Pressure at Sea Level is 1.03 kilogram/centimeter square.It can also be expressed as 10.3 meters of water,in terms of equivalent Water Column or 76 centimeter of Mercury in terms of equivalent Mercury Column.
02)Gauge Pressure:-
It is the Pressure measured by Pressure Measuring Instruments.The Atmospheric Pressure on the Gauge Scale is marked as Zero.Actually Gauge Pressure is always above the Atmospheric Pressure.
03)Absolute Pressure:-
It is defined as the sum of Atmospheric Pressure and Gauge Pressure.In the case of Vacuums,the Gauge Pressure is Minus,then the Absolute Pressure will be,Atmospheric Pressure minus Gauge Pressure.
If the Pressure Intensity at a point is more than the Local Atmospheric Pressure,the difference of these two Pressure Intensity is called "Positive Gauge Pressure".
However,If the Pressure intensity at a point is less than the Local Atmospheric Pressure,the difference of these two Pressure Intensity is called "Negative Gauge Pressure or Vacuum Pressure".
01)Atmospheric Pressure:-
It is established that the Air possesses some Weight and due to its Weight,Air must exert some Pressure on the Surface of the Earth.The Density of Air is different at different heights due to its property of Compressibility.
The Density of Air has also vary from time to time due to change in its Temperature and Humidity.Due to these factors,the Atmospheric Pressure of Air can not be calculated,as is done in case of Liquid.
The Atmospheric Pressure at Sea Level is 1.03 kilogram/centimeter square.It can also be expressed as 10.3 meters of water,in terms of equivalent Water Column or 76 centimeter of Mercury in terms of equivalent Mercury Column.
02)Gauge Pressure:-
It is the Pressure measured by Pressure Measuring Instruments.The Atmospheric Pressure on the Gauge Scale is marked as Zero.Actually Gauge Pressure is always above the Atmospheric Pressure.
03)Absolute Pressure:-
It is defined as the sum of Atmospheric Pressure and Gauge Pressure.In the case of Vacuums,the Gauge Pressure is Minus,then the Absolute Pressure will be,Atmospheric Pressure minus Gauge Pressure.
If the Pressure Intensity at a point is more than the Local Atmospheric Pressure,the difference of these two Pressure Intensity is called "Positive Gauge Pressure".
However,If the Pressure intensity at a point is less than the Local Atmospheric Pressure,the difference of these two Pressure Intensity is called "Negative Gauge Pressure or Vacuum Pressure".
Some Important Terms Used In Hydraulics Engineering.
Hydraulic Machines may be defined as that Branch of Engineering,which deals with the Machine run by Water under some head,or rising the Water to some higher level.
The Properties of Water at rest and at motion:-
01)Water keeps its surface level,at rest
02)The Water exerts a uniform Pressure in all direction.
03)The Velocity of Water,in a channel,is more at the centre than at the sides.
04)The Velocity of Water is directly proportional to the slope of the channel bed.
05)The Pressure of the Water is equal to its Weight and thus,the Pressure increases with the depth.
The Important Properties of Liquid.
01)Density of Water:-
The mass per unit Volume at a standard Temperature and Pressure is known as Density of Liquid.It is denoted by "rho".
02)Specific Weight of Water:-
The Weight per unit Volume,at standard Temperature and Pressure is known as Specific Weight of Liquid.Denoted by "w"
03)Specific Gravity of Water:-
It is the ratio of its Specific Weight to that of a standard substance at a standard Temperature.
04)Compressibility of Water:-
The variation in its Volume,with the variation in its Pressure is known as Compressibility of Water.The Water is considered to be an incompressible liquid.
05)Surface Tension of Water:-
It is the property of Water,which enables it to resist Tensile Stress.It is due to Cohesion between the Molecules at the surface of a liquid.Drops of rain water sphere because liquid surface has a tendency to reduce its surface as small as possible.
06)Capillarity of Water:-
The Phenomenon of rising Water in the tube of smaller diameter is called the Capillary rise.
07)Viscosity of Water:-
The property of Liquid which controls its rate of flow is known as "Viscosity of Water".
Difference between Mass and Weight.
A)MASS:-
It is the amount of matter contained in a given body,and does not vary with the change in its position on the Earth's surface.
B)WEIGHT:-
It is the amount of pull,which the Earth exerts upon a given body,therefore the Weight of the body will vary with its position on the earth's surface.
The Properties of Water at rest and at motion:-
01)Water keeps its surface level,at rest
02)The Water exerts a uniform Pressure in all direction.
03)The Velocity of Water,in a channel,is more at the centre than at the sides.
04)The Velocity of Water is directly proportional to the slope of the channel bed.
05)The Pressure of the Water is equal to its Weight and thus,the Pressure increases with the depth.
The Important Properties of Liquid.
01)Density of Water:-
The mass per unit Volume at a standard Temperature and Pressure is known as Density of Liquid.It is denoted by "rho".
02)Specific Weight of Water:-
The Weight per unit Volume,at standard Temperature and Pressure is known as Specific Weight of Liquid.Denoted by "w"
03)Specific Gravity of Water:-
It is the ratio of its Specific Weight to that of a standard substance at a standard Temperature.
04)Compressibility of Water:-
The variation in its Volume,with the variation in its Pressure is known as Compressibility of Water.The Water is considered to be an incompressible liquid.
05)Surface Tension of Water:-
It is the property of Water,which enables it to resist Tensile Stress.It is due to Cohesion between the Molecules at the surface of a liquid.Drops of rain water sphere because liquid surface has a tendency to reduce its surface as small as possible.
06)Capillarity of Water:-
The Phenomenon of rising Water in the tube of smaller diameter is called the Capillary rise.
07)Viscosity of Water:-
The property of Liquid which controls its rate of flow is known as "Viscosity of Water".
Difference between Mass and Weight.
A)MASS:-
It is the amount of matter contained in a given body,and does not vary with the change in its position on the Earth's surface.
B)WEIGHT:-
It is the amount of pull,which the Earth exerts upon a given body,therefore the Weight of the body will vary with its position on the earth's surface.
Monday
Concept Of Terms Connected With Internal Combustion Engine.
Many different terms are used in Internal Combustion Engines,the important terms which are connected with Internal Combustion Engines are covered in this post.These are follows.
01)Bore:-
The inside Diameter of the Cylinder is known as the Bore and it is measured in millimeter (mm).
02)Stroke:-
It is the distance travelled by the Piston from one of its dead centre position to the other dead centre position.
03)Dead Centre:-
They corresponds to the positions occupied by the piston at the end of its Stroke,where the centre line of the Connecting Rod and Crank are in the same straight line.For Vertical Engines these are known as Top Dead Centre (T.D.C) and Bottom Dead Centre (B.D.C) position.In Horizontal Engines,these are known as Inner Dead Centre (I.D.C) and Outer Dead Centre (O.D.C) position.
04)Top Dead Centre:-
In Vertical Engines,the top most position of the Piston towards the cover end side of the cylinder is known as Top Dead Centre.
05)Bottom Dead Centre:-
In Vertical Engines,the lower position of the Piston towards the Crank end side of the cylinder is known as Bottom Dead Centre.
06)Piston Displacement:-
It is also known as "Swept Volume".It is the volume through which the Piston sweeps for its one Stroke.It is equal to the Area of cross section of the Piston multiplied by its Stroke Length.
07)Clearance Volume:-
It is the Volume included between the Piston and the Cylinder Head when the Piston is at its Top Dead Centre in Vertical Engines and inner Dead Centre in Horizontal Engines.The Clearance Volume is generally expressed as percentages of Swept Volume.
08)Compression Ratio:-
It is the ratio of the total Cylinder Volume to the Clearance Volume.For Petrol Engines the value of Compression Ratio is varies from 5:1 To 9:1 and for Diesel Engines varies from 14:1 To 22:1
09)Piston Speed:-
It is the distance travelled by the Piston in one minute.The piston Speed=2LN meter/min.If the R.P.M. of Engine Shaft=N and length of Stroke=L meter.
10)Crank Throw:-
This is the distance between the Centre of Crankshaft and Centre of Crank Pin.The distance will be equal to half the Stroke Length
01)Bore:-
The inside Diameter of the Cylinder is known as the Bore and it is measured in millimeter (mm).
02)Stroke:-
It is the distance travelled by the Piston from one of its dead centre position to the other dead centre position.
03)Dead Centre:-
They corresponds to the positions occupied by the piston at the end of its Stroke,where the centre line of the Connecting Rod and Crank are in the same straight line.For Vertical Engines these are known as Top Dead Centre (T.D.C) and Bottom Dead Centre (B.D.C) position.In Horizontal Engines,these are known as Inner Dead Centre (I.D.C) and Outer Dead Centre (O.D.C) position.
04)Top Dead Centre:-
In Vertical Engines,the top most position of the Piston towards the cover end side of the cylinder is known as Top Dead Centre.
05)Bottom Dead Centre:-
In Vertical Engines,the lower position of the Piston towards the Crank end side of the cylinder is known as Bottom Dead Centre.
06)Piston Displacement:-
It is also known as "Swept Volume".It is the volume through which the Piston sweeps for its one Stroke.It is equal to the Area of cross section of the Piston multiplied by its Stroke Length.
07)Clearance Volume:-
It is the Volume included between the Piston and the Cylinder Head when the Piston is at its Top Dead Centre in Vertical Engines and inner Dead Centre in Horizontal Engines.The Clearance Volume is generally expressed as percentages of Swept Volume.
08)Compression Ratio:-
It is the ratio of the total Cylinder Volume to the Clearance Volume.For Petrol Engines the value of Compression Ratio is varies from 5:1 To 9:1 and for Diesel Engines varies from 14:1 To 22:1
09)Piston Speed:-
It is the distance travelled by the Piston in one minute.The piston Speed=2LN meter/min.If the R.P.M. of Engine Shaft=N and length of Stroke=L meter.
10)Crank Throw:-
This is the distance between the Centre of Crankshaft and Centre of Crank Pin.The distance will be equal to half the Stroke Length
Sunday
Where we can use Compressed Air.
The power available from compressed air can be used profitably in most industrial fields as a substitute forsteam,electricity or other force. compressed air saves time,cut costs & eases physical burdens.
some typical uses of compressed air are described below.
01) Acid & Chemical Industries :-
Agitation process in liquids can be carried with much ease with the help of compressed air in acid & allied industries. This plays an important part in soda manufacture,in hydrogenationof coal,in manufacture of synthetic ammonia & polymerization of ethylene.
02) Agriculture Industry :-
Compressed air is used in processing of food,farm maintenance by spraying of insectisides,inflating tyers of tractors & trucks.
03) Construction Industry :-
To dig a hole in land for foundation of bridges,building,dam structural work,sewageand tunnel & practically all other types of construction is helped by the compressed air to do the job better and faster.
04) Aircraft Industry :-
Air Operated drills,wrenches & rivetting hammers are used for completing various tasksin aircraft industry.To operate this tools compressed air is used.
05) Ammunation Depots :-
The safety of compressed air is well as its versatility makes it desirable form of powerfor many operations in ammunation depots.air operated ammunation hoists are spark free and quick acting.
06) Mining Operation :-
In mining machine where electric motors or combustion engines can not be usedbecause of risk of fire due to the presence of imflamable fumes & gases.compressed air power is paramountutility in running mining equipments.
07)Manufactureing Industries :-
Compressed air is mostly useful for blowing of pet bottles,to operate pneumaticcylinders,for proper mixing of formulation in pharamaceutical industry.
08) In general :-
Compressed air is used for starting of internal combustion engines,for spray painting,glass blowing.
Compressed air is most useful commodity because it can be store & use whenever we required.production costis less compare to others,neat & clean form of energy.in every industry compressed air is common utility.Few more important topics will be cover in next post.
some typical uses of compressed air are described below.
01) Acid & Chemical Industries :-
Agitation process in liquids can be carried with much ease with the help of compressed air in acid & allied industries. This plays an important part in soda manufacture,in hydrogenationof coal,in manufacture of synthetic ammonia & polymerization of ethylene.
02) Agriculture Industry :-
Compressed air is used in processing of food,farm maintenance by spraying of insectisides,inflating tyers of tractors & trucks.
03) Construction Industry :-
To dig a hole in land for foundation of bridges,building,dam structural work,sewageand tunnel & practically all other types of construction is helped by the compressed air to do the job better and faster.
04) Aircraft Industry :-
Air Operated drills,wrenches & rivetting hammers are used for completing various tasksin aircraft industry.To operate this tools compressed air is used.
05) Ammunation Depots :-
The safety of compressed air is well as its versatility makes it desirable form of powerfor many operations in ammunation depots.air operated ammunation hoists are spark free and quick acting.
06) Mining Operation :-
In mining machine where electric motors or combustion engines can not be usedbecause of risk of fire due to the presence of imflamable fumes & gases.compressed air power is paramountutility in running mining equipments.
07)Manufactureing Industries :-
Compressed air is mostly useful for blowing of pet bottles,to operate pneumaticcylinders,for proper mixing of formulation in pharamaceutical industry.
08) In general :-
Compressed air is used for starting of internal combustion engines,for spray painting,glass blowing.
Compressed air is most useful commodity because it can be store & use whenever we required.production costis less compare to others,neat & clean form of energy.in every industry compressed air is common utility.Few more important topics will be cover in next post.
Saturday
How Internal Combustion Engine is Different From Steam Engine.
To convert Heat energy into Mechanical energy,Internal combustion Engine or Steam Engine are used.Both are heat engines,but both Engines form two different classes of Machines.
They are different in many ways,but following are the important differences in their operations.
01)The working Temperature and Pressure inside the Internal combustion Engines are much higher than those in the Steam Engines.
02)Material with better Resistance are required for Internal combustion Engine as there are very high Temperature and Pressure in Internal combustion Engine comparing to Steam Engine.
03)The Combustion of Fuel,taken place inside the Engine Cylinder in case of Internal combustion Engine,while in Steam Engine Fuel is burnt in a Boiler to raise the Steam which in turns is used in the Engine cylinder.
04)Stuffing Box Glands for Connecting Rod are avoided in Internal combustion Engine as these are mostly Single Acting Cylinder Engine.In Steam Engine Stuffing Box Glands are required for Piston Rod.
05)The efficiency of Internal combustion Engine is as high as 35 to 40 % as compared to that of Steam Engines which have efficiency is near about 10 to 15%.
Advantages of Internal combustion Engine over Steam Engine.
01)It has higher efficiency
02)It has low weight to power ratio because of its compact design.
03)It can be started instantaneously,in Steam engine Boiler has to be fired and Steam raised before the Engine can be started.
They are different in many ways,but following are the important differences in their operations.
01)The working Temperature and Pressure inside the Internal combustion Engines are much higher than those in the Steam Engines.
02)Material with better Resistance are required for Internal combustion Engine as there are very high Temperature and Pressure in Internal combustion Engine comparing to Steam Engine.
03)The Combustion of Fuel,taken place inside the Engine Cylinder in case of Internal combustion Engine,while in Steam Engine Fuel is burnt in a Boiler to raise the Steam which in turns is used in the Engine cylinder.
04)Stuffing Box Glands for Connecting Rod are avoided in Internal combustion Engine as these are mostly Single Acting Cylinder Engine.In Steam Engine Stuffing Box Glands are required for Piston Rod.
05)The efficiency of Internal combustion Engine is as high as 35 to 40 % as compared to that of Steam Engines which have efficiency is near about 10 to 15%.
Advantages of Internal combustion Engine over Steam Engine.
01)It has higher efficiency
02)It has low weight to power ratio because of its compact design.
03)It can be started instantaneously,in Steam engine Boiler has to be fired and Steam raised before the Engine can be started.
Details Of Crankshaft Used In Internal Combustion Engine.
In Internal combustion Engine various parts are used to perform it as a Machine,out of that Crankshaft is one of the most important part used in I.C. Engine.
The construction and its details are as below.
To convert Reciprocating motion of the Piston into Rotary motion,the Crankshaft and Connecting Rod combination is used.The Crankshaft which is made by Steel Forging or Casting is held on the Axis around which it rotates,by the Main Bearings,which is fit round the main Journals provided.
There are always at least two such bearings,one at the rare end and other at front end.the increase in number of Main Bearings for a given size of the Crankshaft means less possibility of Vibration and Distortion.
But it will also increase the difficulty of correct alignment in addition to increased production cost.
The Main Bearings are mounted on the Crankcase of the Engine.The Balance weight or Counter weight keep the system in perfect balance.
The Crank Webs are extended and enlarged on the side of Journal opposite the Crank Throw so as to from balance weights.
The Crankshaft may be made from Carbon Steel,Nickel Chrome or other Alloy Steel.
The description of some other important parts will be covered in coming posts.
The construction and its details are as below.
To convert Reciprocating motion of the Piston into Rotary motion,the Crankshaft and Connecting Rod combination is used.The Crankshaft which is made by Steel Forging or Casting is held on the Axis around which it rotates,by the Main Bearings,which is fit round the main Journals provided.
There are always at least two such bearings,one at the rare end and other at front end.the increase in number of Main Bearings for a given size of the Crankshaft means less possibility of Vibration and Distortion.
But it will also increase the difficulty of correct alignment in addition to increased production cost.
The Main Bearings are mounted on the Crankcase of the Engine.The Balance weight or Counter weight keep the system in perfect balance.
The Crank Webs are extended and enlarged on the side of Journal opposite the Crank Throw so as to from balance weights.
The Crankshaft may be made from Carbon Steel,Nickel Chrome or other Alloy Steel.
The description of some other important parts will be covered in coming posts.
Friday
10 Major Parts of Reciprocating Air Compressor.
The Air Compressor is manufactured by assembling of various components.All the parts are importantfor working of air compressor but one who is interested to learn about air compressor must familiar with below parts.
01) Frame/Crankcase :-
Totally enclosed,rigid cast iron body in square or rectangle shape.Bearing housing is fitted on crank case with accurately bored to fit Main Bearings so,misalignment or eccentricity is avoided.It gives better support to the crank shaft.
02) Crank Shaft :-
High grade S.G. Iron crank shaft in one piece in design,dynamically balancedwith counter weights,avoid any twisting.Crank pin & Jouranals duly ground & polished,ensure long life of bearings. A Flywheel is fitted on crank shaft.
03)Connecting Rod :-
Forged alloy steel connecting rod is duly normalised,are designed to provideminimum thrust on cross head bearing surface.
04) Main Bearings & Big End Bearings :-
Copper lead alloy designed for long life.It gives perfectrigidity to running gear.
05) Cross Slide & Cross Head :-
Manufactured from High grade S.G. Iron material.Its low inertia along with low friction cross slide ensure perfect running of cross head.
06)Cylinders :-
Graded Cast Iron cylinders designed with water jacket in water cooled air compressorto remove heat generated during compression.Designed for streamlined air passage & maximumnumbers of valves,cylinder provide smooth flow of air,there by minimizing the pressure drop.
07) Pistons :-
Special Aluminium alloy pistons for non-lubricated air compressor and graded castiron pistons are for lubricated models.Piston Rings are used for sealing to cylinder.
08) Piston Rod :-
Alloy Steel piston rods fitted with wear resistant packing rings of antifriction typeto prevent any possibility of c ompressed air leakage.
09) Suction & Discharge Valves :-
Stainless Steel plate type or spring type valves are arranged symmetrically in suction & discharge,provides longer life.
10) Oil Pump :-
It feeds oil to main bearings,connecting rod bearings & to cross slides.The oil pumpregulates the oil pressure by pressure regulating screw.
Above are few important parts used in Reciprocating Air Compressor.
Along with this parts some small parts are also used in air compressor,details of these parts you will find in comming posts.
01) Frame/Crankcase :-
Totally enclosed,rigid cast iron body in square or rectangle shape.Bearing housing is fitted on crank case with accurately bored to fit Main Bearings so,misalignment or eccentricity is avoided.It gives better support to the crank shaft.
02) Crank Shaft :-
High grade S.G. Iron crank shaft in one piece in design,dynamically balancedwith counter weights,avoid any twisting.Crank pin & Jouranals duly ground & polished,ensure long life of bearings. A Flywheel is fitted on crank shaft.
03)Connecting Rod :-
Forged alloy steel connecting rod is duly normalised,are designed to provideminimum thrust on cross head bearing surface.
04) Main Bearings & Big End Bearings :-
Copper lead alloy designed for long life.It gives perfectrigidity to running gear.
05) Cross Slide & Cross Head :-
Manufactured from High grade S.G. Iron material.Its low inertia along with low friction cross slide ensure perfect running of cross head.
06)Cylinders :-
Graded Cast Iron cylinders designed with water jacket in water cooled air compressorto remove heat generated during compression.Designed for streamlined air passage & maximumnumbers of valves,cylinder provide smooth flow of air,there by minimizing the pressure drop.
07) Pistons :-
Special Aluminium alloy pistons for non-lubricated air compressor and graded castiron pistons are for lubricated models.Piston Rings are used for sealing to cylinder.
08) Piston Rod :-
Alloy Steel piston rods fitted with wear resistant packing rings of antifriction typeto prevent any possibility of c ompressed air leakage.
09) Suction & Discharge Valves :-
Stainless Steel plate type or spring type valves are arranged symmetrically in suction & discharge,provides longer life.
10) Oil Pump :-
It feeds oil to main bearings,connecting rod bearings & to cross slides.The oil pumpregulates the oil pressure by pressure regulating screw.
Above are few important parts used in Reciprocating Air Compressor.
Along with this parts some small parts are also used in air compressor,details of these parts you will find in comming posts.
How to Start and Stop Air Compressor.
Air Compressor will give the best performance when it is operated by due care taken.Every machine has its own requirment of starting and stopping.
This is the machine which may run for several weeks without stopping or some times required to keep idle for many days or week.Every operator must have to know the routine stating and stopping of Air Compressor,to obtain best result from the machine.Here i will cover most of them,follow it.
Routine Starting of Air Compressor.
01)Keep Air Compressor at Unload condition by use of Unloaders.
02)Turn on cooling water to remove air lock from water cooling system.
03)Ensure belt wheel is free to rotate by rotating it by hand,for several rotations.
04)If force feed lubricator if fitted,check oil level and operate it for 8-10 turns.
05)Check position of safety shut down switches.
06)Drain Condensate from Intercooler & Aftercooler.
07)Check V-belt tighteness.
08)Check position of stop valve,open it,to flow compressed air to receiver.
09)Start Air compressor.
10)Check oil pressure.
11)Check oil flow from each lubricator pump.
12)Load Air Compressor after 3 to 5 minutes of operation.
13)Regulate water flow to cylinder,intercooler and aftercooler.
14)Check Interstage Pressure.
15)Check for leaks in Air,Water and oil lines.
16)Check Voltage available to each terminals and current drawn by the motor.
17)Check Discharge air temperature.
18)Drain condensed water from Air Receiver,Pulsation bottles and moisture seperators.
19)Check for loose nut and bolts,tighten if required.
20)Check for unusual noises.
Procedure for stopping the Air Compressor.
01)Unload Air compressor by using unloader and allow compressor to run for 5 minutes.
02)Stop Electric Motor.
03)Shut off cooling water
04)Drain condesed water from collection points.
05)Discontuine Power supply to starter.
If any one follow above precautions,there Air Compressor will give best performance for long period.
This is the machine which may run for several weeks without stopping or some times required to keep idle for many days or week.Every operator must have to know the routine stating and stopping of Air Compressor,to obtain best result from the machine.Here i will cover most of them,follow it.
Routine Starting of Air Compressor.
01)Keep Air Compressor at Unload condition by use of Unloaders.
02)Turn on cooling water to remove air lock from water cooling system.
03)Ensure belt wheel is free to rotate by rotating it by hand,for several rotations.
04)If force feed lubricator if fitted,check oil level and operate it for 8-10 turns.
05)Check position of safety shut down switches.
06)Drain Condensate from Intercooler & Aftercooler.
07)Check V-belt tighteness.
08)Check position of stop valve,open it,to flow compressed air to receiver.
09)Start Air compressor.
10)Check oil pressure.
11)Check oil flow from each lubricator pump.
12)Load Air Compressor after 3 to 5 minutes of operation.
13)Regulate water flow to cylinder,intercooler and aftercooler.
14)Check Interstage Pressure.
15)Check for leaks in Air,Water and oil lines.
16)Check Voltage available to each terminals and current drawn by the motor.
17)Check Discharge air temperature.
18)Drain condensed water from Air Receiver,Pulsation bottles and moisture seperators.
19)Check for loose nut and bolts,tighten if required.
20)Check for unusual noises.
Procedure for stopping the Air Compressor.
01)Unload Air compressor by using unloader and allow compressor to run for 5 minutes.
02)Stop Electric Motor.
03)Shut off cooling water
04)Drain condesed water from collection points.
05)Discontuine Power supply to starter.
If any one follow above precautions,there Air Compressor will give best performance for long period.
Why Octane Value Of Fuels Are So Imporatant?
Detonation means the sudden and violent knock experienced in a Petrol Engine,due to Anti-Ignition of a portion of the Fuel.The Octane Value of the Fuel will give us an idea of the tendency of the fuel to detonate.
This is mainly important in Spark Ignition Engines.To find it out,two Fuels,the iso-octane and the normal Leptane are selected for this purpose under modern practise.
The iso-Octane has little tendency towards detonation while Leptane,readily detonates.The actual fuel whose Octane Value is to be determined is first used to run standard engine and the conditions under which detonation occurs are noted.
The Detonation intensity is measured by "Knock Meter".Then several mixtures of iso-Octane and normal Heptane mixed up in different proportions are used in the same engine,under the same conditions,as before.
By making several trials,the mixture which gives the same intensity of Detonation is found out.
The percentage of iso-octane in this mixture gives the octane value of the Fuel.For example,with the mixture containing 75% of iso-Octane and 25% of normal Heptane,the Octane Value of the Fuel will be 75.
Higher the Octane Value,higher the Anti-knocking property of the Fuel.The Octane Value of the pure iso-Octane and normal Heptane are 100 and 0respectively.
The Octane rating indicates the quality of the petrol to resist detonation.
This is mainly important in Spark Ignition Engines.To find it out,two Fuels,the iso-octane and the normal Leptane are selected for this purpose under modern practise.
The iso-Octane has little tendency towards detonation while Leptane,readily detonates.The actual fuel whose Octane Value is to be determined is first used to run standard engine and the conditions under which detonation occurs are noted.
The Detonation intensity is measured by "Knock Meter".Then several mixtures of iso-Octane and normal Heptane mixed up in different proportions are used in the same engine,under the same conditions,as before.
By making several trials,the mixture which gives the same intensity of Detonation is found out.
The percentage of iso-octane in this mixture gives the octane value of the Fuel.For example,with the mixture containing 75% of iso-Octane and 25% of normal Heptane,the Octane Value of the Fuel will be 75.
Higher the Octane Value,higher the Anti-knocking property of the Fuel.The Octane Value of the pure iso-Octane and normal Heptane are 100 and 0respectively.
The Octane rating indicates the quality of the petrol to resist detonation.
Thursday
Why Antifreezers Are Required To Be Used In Engines?
Some heat is generated in Cylinder when Engine is in working condition.To keep Cylinder in cool condition Air or Water is used as Cooling Media.When the Engine is cooled by circulating water around Cylinder then the Engine is called 'Water Cooled Engine".
If the Engine is kept idle (without use) for long time there is a possibility of freezing of water.This mostly happens in Winter.
The water may freeze and expands leading to fracture in Water Jackets,Water Circulating Pipe or Radiator.To lower the freezing Temperature,certain mixture are added to water.This mixture are known as "Antifreezers".
To avoid the wastage of Antifreezers due to Evaporation,its boiling point should be as high as of water.
The important qualities of ideal Antifreezers.
01)It should easily dissolve in water.
02)It should be reasonably cheap.
03)Should not deposit any foreign matters in the Water Jackets,Pipes and cause no harmful effects to any part of Cooling System.
No single Antifreezers satisfies all these requirements.The material in common use are Glycerine,Ethylene Glycol,Propylene,Alcohol and mixture of Glycerine and Alcohol.If Alcohol is used,frequent checking with a Hydrometer is required.Glycerin,Ehtylene and Propylene Glycol though have high initial cost,prove cheap in long run,provided proper care is taken against leakage,because there mixture do not Evaporate.
If the Engine is kept idle (without use) for long time there is a possibility of freezing of water.This mostly happens in Winter.
The water may freeze and expands leading to fracture in Water Jackets,Water Circulating Pipe or Radiator.To lower the freezing Temperature,certain mixture are added to water.This mixture are known as "Antifreezers".
To avoid the wastage of Antifreezers due to Evaporation,its boiling point should be as high as of water.
The important qualities of ideal Antifreezers.
01)It should easily dissolve in water.
02)It should be reasonably cheap.
03)Should not deposit any foreign matters in the Water Jackets,Pipes and cause no harmful effects to any part of Cooling System.
No single Antifreezers satisfies all these requirements.The material in common use are Glycerine,Ethylene Glycol,Propylene,Alcohol and mixture of Glycerine and Alcohol.If Alcohol is used,frequent checking with a Hydrometer is required.Glycerin,Ehtylene and Propylene Glycol though have high initial cost,prove cheap in long run,provided proper care is taken against leakage,because there mixture do not Evaporate.
Different Ignition Systems Of Internal Combustion Engines.(Part-B)
If the Ignition in Internal Combustion Engines takes place at the end of Compression Stroke then the engine runs without knocks,with good efficiency.
The Compression Ignition Engines are so design that the temperature at the end of the Compression is above the self-Ignition Temperature of Fuel. In this case,no spark plug as like in Spark Ignition required for Ignition.
Basically Four methods are used for Ignition.Out of that,Hot Tube Ignition Method and,Spark Ignition method are covered in last post.Remaining two will be covered in this post.That are as follows
03)Hot Combustion Chamber Ignition:-
The another name of this method is "Surface Ignition or Hot Surface Ignition".This method is used in Engines working on "Dual Combustion Cycle".The fuel is Ignited by being injected into a Hot Tube or Combustion Chamber containing Compressed Air.
The bulb which is located at the compression end of the Engine Cylinder and connected by a narrow space or throat to the combustion space of the cylinder is unjacketed and initially heated from an external source,like Lamp.At the end of Compression Stroke the Fuel is injected comes in contact with the red hot bulb and thus the ignition commences.
Once the Engine starts the heat retained from the previous explosion is sufficient to ignite the fuel in the next cycle.
04)Compression Ignition:-
This method is used in heavy oil engines working on Constant Pressure Cycle (Diesel Cycle).The Air is Compressed to such a high Pressure that its Temperature is higher than that at which the fuel burns.The Fuel is then injected into this hot compressed air where its ignition start spontaneously.
In Hot Tube Ignition and Hot Combustion Chamber Ignition,the exact point of the cycle at which ignition commences is quite uncertain.This problem does not occurs in Compression Ignition.
The Compression Ignition Engines are so design that the temperature at the end of the Compression is above the self-Ignition Temperature of Fuel. In this case,no spark plug as like in Spark Ignition required for Ignition.
Basically Four methods are used for Ignition.Out of that,Hot Tube Ignition Method and,Spark Ignition method are covered in last post.Remaining two will be covered in this post.That are as follows
03)Hot Combustion Chamber Ignition:-
The another name of this method is "Surface Ignition or Hot Surface Ignition".This method is used in Engines working on "Dual Combustion Cycle".The fuel is Ignited by being injected into a Hot Tube or Combustion Chamber containing Compressed Air.
The bulb which is located at the compression end of the Engine Cylinder and connected by a narrow space or throat to the combustion space of the cylinder is unjacketed and initially heated from an external source,like Lamp.At the end of Compression Stroke the Fuel is injected comes in contact with the red hot bulb and thus the ignition commences.
Once the Engine starts the heat retained from the previous explosion is sufficient to ignite the fuel in the next cycle.
04)Compression Ignition:-
This method is used in heavy oil engines working on Constant Pressure Cycle (Diesel Cycle).The Air is Compressed to such a high Pressure that its Temperature is higher than that at which the fuel burns.The Fuel is then injected into this hot compressed air where its ignition start spontaneously.
In Hot Tube Ignition and Hot Combustion Chamber Ignition,the exact point of the cycle at which ignition commences is quite uncertain.This problem does not occurs in Compression Ignition.
Different Ignition Systems Of Internal Combustion Engines.(Part-A)
There are Four different methods by which Fuel may be Ignited in Internal Combustion (IC) Engines.In my earlier post,you have come to know about Comparison of Coil & Magneto Ignition Systems.That Systems are under Spark Ignition System,as like this another Three Systems are as,
01)Hot Tube Ignition.
02)Hot Combustion Chamber Ignition.
03)Compression Ignition.
We will see two Systems in this part and another two,in the next part-B
01)Hot Tube Ignition Method:-
This is the old method which was used in old days,now this method has become obsolete.But to gain some knowledge,here I disclose some description.This method used in Gas and Light Oil Engines,a porcelain or metal tube closed one end is heated red hot from an external source,to Temperature well above the Ignition Temperature of the Fuel so that when the latter is injected into the tube it immediately ignites.
The tube is heated at middle,through a Timing Valve,the hot tube communicates alternatively with the Cylinder when Ignition takes place and with the Atmosphere during expansion.In some Gas Engines this Timing Valve has been dispensed with and the ignition tube is in free communication with the Cylinder throughout,the instant of firing being determined by Compression of some of the Explosive Mixture into to the tube.As the Engine starts the heat of the tube from the previous explosion is sufficient to ignite the Fuel in the next cycle.
02)Spark Ignition:-
This method is mostly used on Engine working on "Otto Cycle" and consists in ignite the Fuel by producing a high tension Electric Spark.The Engines which are using this type of Ignition method are called "Spark Ignition Engines".In which one Spark must be produced at each cylinder at the correct moment.
Remaining two methods are covered in next post.
01)Hot Tube Ignition.
02)Hot Combustion Chamber Ignition.
03)Compression Ignition.
We will see two Systems in this part and another two,in the next part-B
01)Hot Tube Ignition Method:-
This is the old method which was used in old days,now this method has become obsolete.But to gain some knowledge,here I disclose some description.This method used in Gas and Light Oil Engines,a porcelain or metal tube closed one end is heated red hot from an external source,to Temperature well above the Ignition Temperature of the Fuel so that when the latter is injected into the tube it immediately ignites.
The tube is heated at middle,through a Timing Valve,the hot tube communicates alternatively with the Cylinder when Ignition takes place and with the Atmosphere during expansion.In some Gas Engines this Timing Valve has been dispensed with and the ignition tube is in free communication with the Cylinder throughout,the instant of firing being determined by Compression of some of the Explosive Mixture into to the tube.As the Engine starts the heat of the tube from the previous explosion is sufficient to ignite the Fuel in the next cycle.
02)Spark Ignition:-
This method is mostly used on Engine working on "Otto Cycle" and consists in ignite the Fuel by producing a high tension Electric Spark.The Engines which are using this type of Ignition method are called "Spark Ignition Engines".In which one Spark must be produced at each cylinder at the correct moment.
Remaining two methods are covered in next post.
Wednesday
The Important Fuel Injection Method Used In Compression Ignition Engines.
Proper fuel Injection in Engine is most important fact in any Diesel Engine.Mostly two methods are in use for Fuel Injection.
01)Air Blast Injection:-
This is old method which is obsolete now a days.In this method Air is Compressed at very high pressure by means of a Air Compressor.A blast of this Air is then injected carrying the Fuel along with it into the Cylinder.
Due to varying Pressure of Injection Air the rate at which the fuel is admitted can be effectively controlled.The combustion takes place nearly at constant Pressure.Due to high Pressure Air Compressor weight increase and net output of Engine is decrease.
02)Solid Injection:-
This Air less Injection System.The Fuel under Pressure is directly injected into the combustion Chamber at Atomised State.This is useful for small and big Diesel Engines.It requires a Pump to deliver the fuel at High Pressure.This Fuel Injection System further divided into two system.
A)Individual Pump System:-
In this system each cylinder has its own individuals High pressure Pump and a metering unit.This is quite compact system.It has a higher manufacturing cost due to close tolerance are required at production.
B)Common Rail System:-
The Fuel is pumped by a Multi-Cylinder Pump into a common rail,the pressure in which is controlled by a Relief Valve.
The Advantages of Solid Injection System.
01)Simple in construction.
02)Lighter in weight.
03)Lower Fuel consumption.
04)Lower initial cost.
05)No High Pressure Air compressor required to start the Engine.
01)Air Blast Injection:-
This is old method which is obsolete now a days.In this method Air is Compressed at very high pressure by means of a Air Compressor.A blast of this Air is then injected carrying the Fuel along with it into the Cylinder.
Due to varying Pressure of Injection Air the rate at which the fuel is admitted can be effectively controlled.The combustion takes place nearly at constant Pressure.Due to high Pressure Air Compressor weight increase and net output of Engine is decrease.
02)Solid Injection:-
This Air less Injection System.The Fuel under Pressure is directly injected into the combustion Chamber at Atomised State.This is useful for small and big Diesel Engines.It requires a Pump to deliver the fuel at High Pressure.This Fuel Injection System further divided into two system.
A)Individual Pump System:-
In this system each cylinder has its own individuals High pressure Pump and a metering unit.This is quite compact system.It has a higher manufacturing cost due to close tolerance are required at production.
B)Common Rail System:-
The Fuel is pumped by a Multi-Cylinder Pump into a common rail,the pressure in which is controlled by a Relief Valve.
The Advantages of Solid Injection System.
01)Simple in construction.
02)Lighter in weight.
03)Lower Fuel consumption.
04)Lower initial cost.
05)No High Pressure Air compressor required to start the Engine.
How Mico Fuel Injection System Works?
Mico Fuel injection System used for Multi-Cylinder Diesel Engines.The system consists of a Fuel Feed Pump and a Fuel Injection Pump which are integrated in one body.
The Fuel Feed Pump sucks the Fuel Oil from the fuel tank which still contains Air bubbles and Vapour,then the Pump supply oil to filter unit for purifying it.The filter unit cleans the oil and further supply it to the Fuel injection Pump.Overflowed oil is sent back to Fuel Tank through overflow valve provided on the filter unit.Air vent screw is also provided on the Filter unit for Air Venting.
The injection Pump has a main Crank Shaft which is driven by power supplied by the Engine.The number of Plunger quantity is equal to number of Cylinder in Engine.One Plunger supplies the fuel to one cylinder of Engine only,and each Plunger works as an individual Injection Pump.Only Control Rod meshes with all the toothed quadrants of all the Pumps at the same time.
The Fuel which is coming from Filter unit is compressed to the required pressure by these Plungers and is supplied through delivery pipe to the injector of the Engine at proper timing.Separate overflow outlets are provided on each plunger to sent back overflowed oil to Fuel Tank.
A Governor is also provided in the Injection Pump,which actuates the control rod to govern the supply of oil through plunger according to the demand of the Engine.
The Fuel Feed Pump sucks the Fuel Oil from the fuel tank which still contains Air bubbles and Vapour,then the Pump supply oil to filter unit for purifying it.The filter unit cleans the oil and further supply it to the Fuel injection Pump.Overflowed oil is sent back to Fuel Tank through overflow valve provided on the filter unit.Air vent screw is also provided on the Filter unit for Air Venting.
The injection Pump has a main Crank Shaft which is driven by power supplied by the Engine.The number of Plunger quantity is equal to number of Cylinder in Engine.One Plunger supplies the fuel to one cylinder of Engine only,and each Plunger works as an individual Injection Pump.Only Control Rod meshes with all the toothed quadrants of all the Pumps at the same time.
The Fuel which is coming from Filter unit is compressed to the required pressure by these Plungers and is supplied through delivery pipe to the injector of the Engine at proper timing.Separate overflow outlets are provided on each plunger to sent back overflowed oil to Fuel Tank.
A Governor is also provided in the Injection Pump,which actuates the control rod to govern the supply of oil through plunger according to the demand of the Engine.
Tuesday
Comparison Of The Magneto And Coil Ignation System.
Different types of Ignition Systems are used in Internal Combustion (I.C) Engine.Out of that Magneto and Coil Ignition System are more important.Here you will find some comparison between these two systems.
Comparison of the Magneto and Coil Ignition System.
01)Cost:-
The Manufacturing cost of Coil Ignition System is low,due to less precision work than to Magneto Ignition System.
02)Simplicity:-
The Wiring in the Coil Ignition System is quite complicated hence this system requires greater attention against possible defects.But in Magneto ignition system the wiring is comparatively simple and it forms a compact unit.
03)Dependence on Battery and Charging Dynamo:-
Condition of the Battery and Charging Dynamo will greatly influenced in operation of the Coil Ignition System.If the Battery gets discharges,it becomes very difficult to start the engine by hand cranking.This difficulty will not experienced in Magneto Ignition System,which is more reliable.
04)Starting and Low Speed Operation:-
A good Spark will get in Coil Ignition System at starting in spite low speed.The strength of the Spark in Magneto Ignition System at the time of starting and at low speed is very low.
05)Strength and Spark at High Speed:-
With the increase in speed the strength of the Spark given by the Magneto Ignition System increase but it decrease in the case of Coil Ignition System.Coil Ignition System can not be used in High Speed Racing Cars and in Aeroplanes.
Comparison of the Magneto and Coil Ignition System.
01)Cost:-
The Manufacturing cost of Coil Ignition System is low,due to less precision work than to Magneto Ignition System.
02)Simplicity:-
The Wiring in the Coil Ignition System is quite complicated hence this system requires greater attention against possible defects.But in Magneto ignition system the wiring is comparatively simple and it forms a compact unit.
03)Dependence on Battery and Charging Dynamo:-
Condition of the Battery and Charging Dynamo will greatly influenced in operation of the Coil Ignition System.If the Battery gets discharges,it becomes very difficult to start the engine by hand cranking.This difficulty will not experienced in Magneto Ignition System,which is more reliable.
04)Starting and Low Speed Operation:-
A good Spark will get in Coil Ignition System at starting in spite low speed.The strength of the Spark in Magneto Ignition System at the time of starting and at low speed is very low.
05)Strength and Spark at High Speed:-
With the increase in speed the strength of the Spark given by the Magneto Ignition System increase but it decrease in the case of Coil Ignition System.Coil Ignition System can not be used in High Speed Racing Cars and in Aeroplanes.
What Are The Different Methods Of Heating And Expanding Gases.
Various methods are used engineering for heating and expanding the Gases.these methods are also applicable to the contraction or cooling of gases.The contraction means negative expansion and cooling means negative heating.
01)Constant Volume Process:-
There will be no change in Volume and no external work will be done by the gas,when a Gas is heated in a fixed enclosed space.Due to heating,Pressure and Temperature will rise and the whole heat supplied will be stored in the form of Internal Energy.
02)Constant Pressure Process:-
When a Gas is heated at constant Pressure,the Volume and the Temperature of a Gas will increase.There will be some external work done due to increase in Volume.
03)Constant Temperature Process:-
This is also known as "Isothermal Process".When a heat is supplied to a gas at constant Temperature,the expansion occurred is called "Isothermal Expansion".The whole of the heat supplied to the Gas will be used up in doing external work.
04)Hyperbolic Process:-
When a Gas is heated in such a way that its Pressure multiplied by its Volume remain constant,the expansion called "Hyperbolic".
PRESSURE x VOLUME= CONSTANT.
The workdone and the heat supplied are same.This identical only in the case of Perfect Gas and not for vapours.
05)Reversible Adiabatic Process:-
This is also called as "Isentropic Process".The system neither receives nor gives out heat to the surrounding.This means no exchange of heat between the system and the surrounding.
06)Polytropic Process:-
This process follows the general Law ( PRESSURE x VOLUME raise to n equals to Constant) where the index "n" may have any value depending upon the method of carrying out expansion.
07)Free Expansion:-
This is said to be occurred,when a fluid suddenly expands into a Vacuum Chamber through an Orifice of large dimension.No heat is supplied or rejected,there is no workdone and the Temperature during this process remains constant.
08)Throttling Process:-
This type of expansion occures when a Gas or vapour is expanded through an Aperture of minute dimension like a valve which is very slightly opened or a narrow throat.In Throttling Process,if it is a perfect gas ,there is no change in Temperature.
01)Constant Volume Process:-
There will be no change in Volume and no external work will be done by the gas,when a Gas is heated in a fixed enclosed space.Due to heating,Pressure and Temperature will rise and the whole heat supplied will be stored in the form of Internal Energy.
02)Constant Pressure Process:-
When a Gas is heated at constant Pressure,the Volume and the Temperature of a Gas will increase.There will be some external work done due to increase in Volume.
03)Constant Temperature Process:-
This is also known as "Isothermal Process".When a heat is supplied to a gas at constant Temperature,the expansion occurred is called "Isothermal Expansion".The whole of the heat supplied to the Gas will be used up in doing external work.
04)Hyperbolic Process:-
When a Gas is heated in such a way that its Pressure multiplied by its Volume remain constant,the expansion called "Hyperbolic".
PRESSURE x VOLUME= CONSTANT.
The workdone and the heat supplied are same.This identical only in the case of Perfect Gas and not for vapours.
05)Reversible Adiabatic Process:-
This is also called as "Isentropic Process".The system neither receives nor gives out heat to the surrounding.This means no exchange of heat between the system and the surrounding.
06)Polytropic Process:-
This process follows the general Law ( PRESSURE x VOLUME raise to n equals to Constant) where the index "n" may have any value depending upon the method of carrying out expansion.
07)Free Expansion:-
This is said to be occurred,when a fluid suddenly expands into a Vacuum Chamber through an Orifice of large dimension.No heat is supplied or rejected,there is no workdone and the Temperature during this process remains constant.
08)Throttling Process:-
This type of expansion occures when a Gas or vapour is expanded through an Aperture of minute dimension like a valve which is very slightly opened or a narrow throat.In Throttling Process,if it is a perfect gas ,there is no change in Temperature.
Subscribe to:
Posts (Atom)
Custom Search
