Parts of Steam Engine and Its Functions.

Steam engines are used very widely in engineering up to 1930 for generation of power but after it are replaced by internal combustion engine. Diesel engine, petrol engine are the common example of internal combustion engine. Steam engines are widely used on ships in old days at present they are replaced by diesel engines. To disclose some more important information about this old machine, I am giving some details about its parts and their functions in operating.

01) Frame: -
It is the heavy casting which supports all the stationary and moving parts of the engine and holds them in proper alignment. It requires foundation to rest upon or engine bed plate fixed on engine foundation.

02) Cylinder: -
It is the cast iron cylindrical hollow vessel in which the piston moves to and fro under the pressure of steam. Crank side end and outer end of cylinder is closed by end covers and made steam-tight.

03) Steam Chest: -
It is the closed chamber integral with the cylinder. It supplies steam to the cylinder with the movement of slide valve.

04) Stuffing Box and Gland: -
This part is fitted on the crank end cover of the cylinder and their function is to prevent the leakage of steam past the piston rod.

05) Piston: -
It is the cast iron cylindrical disc moving to and fro in the cylinder under the action of the steam pressure. This part converts heat energy of steam into mechanical work. Cast iron piston rings make the piston steam tight in the cylinder and thereby prevent the leakage of steam past the piston.

06) Cross head: -
It is the link between piston rod and the connecting rod. It guides the motion of the piston rod and prevents it from bending.

07) Connecting Rod: -
It is cast iron part which helps to convert reciprocating motion of piston into rotary motion of the crank. Gudgeon pin is used to connect one end of connecting rod to cross head and its open end is connected to the crankshaft.

08) Crankshaft: -
It is made from mild steel on which flywheel is mounted on it. It is supported on the main bearings of the engine and it is free to rotate in them.

09) Slide Valve: -
Fixed on the steam chest and its function are to admit the steam from steam chest to the cylinder, and exhaust the steam from the cylinder at the proper moment. The valve gets to and fro motion from the eccentric fitted on the crankshaft.

10) Main Bearings: -
This part support crank shaft and fitted in the engine frame known as main bearing journal.

11) Flywheel: -
It is made from cast iron or cast steel and mounted on the crankshaft to prevent the fluctuation of engine speed throughout the stroke and to carry the crank smoothly over the dead centers.

12) Governor: -
To control the speed of the engine according to the load conditions, the governor is used. The speed of the engine is controls either by the quantity or pressure of the steam supplied to the engine.

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Important Characteristics in formation of Steam.

When any liquid is heated at constant temperature, it starts changing in vapour condition. A vapour is a mixture of gas and liquid particles in suspension and it can be liquefied by moderate changes of pressure or temperature. The process of vapour formation from liquid state has some definite characteristics to follow in steam engine,

Characteristics of Steam formation.

01) The heat supplied during the process of vapourization changes its state gradually from liquid to gaseous state.

02) The vapour is said to be dry saturated when the process of vapourization takes place at constant pressure and temperature. In other word we can say when the liquid is completely evaporated it is called dry saturated.

03) The vapour is called superheated when the heat is added to the dry saturated vapour state. At superheated state, the temperature will rise gradually.

04) During the process of superheating a vapour at constant pressure, the volume will increase approximately in proportion to the absolute temperature, which indicates that the vapour is approaching the state of perfect gas.

05) The temperature at which the evaporation process is taking place is increase when the pressure on the liquid surface is increased

06) The latent heat of vaporization decrease with the increase of pressure and temperature but the sensible enthalpy increases under this condition.

07) The total heat (Enthalpy) of dry saturated vapour increases with increase in saturation temperature. In lower range of pressure and temperature, the rate of increase in sensible enthalpy is greater than the rate of decrease in latent enthalpy with the increase in pressure.

After certain saturation temperature the rate of increase in sensible enthalpy is less than the rate of decrease in latent enthalpy and hence, the enthalpy of dry saturated vapour decreases. This will continue to happen until the saturation temperature is reached when the latent enthalpy becomes zero and the enthalpy of dry saturated vapour becomes equal to the sensible heat.

This saturation temperature is called as critical temperature and the corresponding pressure is called critical pressure and the state of substance is called its critical state.

08) Steam can not exist as saturated vapour above its critical temperature. At any temperature higher than the critical temperature (374.14 degree centigrade) the vapour can only exist as a gas without any effect of pressure.
At critical temperature, the specific volume of dry saturated vapour becomes equal to the specific volume of the liquid from which it is being formed.


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Various Important Properties of Substance.

In thermal engineering, State means the exact condition of a substance and the variables which determine the state are known as properties. These properties are sub-divided into principal properties and fundamental properties. Fundamental properties are,

01) Pressure
02) Volume
03) Temperature

Above properties are also known as basic properties as they may be found out by direct observation or simple measurements. You will found details about these properties as below,

01) Pressure: -It is the force applied over a unit area. In international system (SI) of units, the unit for pressure is the force of one Newton (N) acting on a square meter area which is known as Pascal (Pa) so,

1 Pa = 1 N/meter square
1 Kilo pascal = 1000 Pa = 1 KPa
1 Mega Pascal = 10, 00,000 Pa = 1 MPa

Other unit for pressure is bar and atmosphere pressure (atm.)
Gauges are used to measure the pressure of fluid. Pressure gauges which used to measure

The pressure which is greater than atmosphere where as the vacuum gauges is used to measure pressure less than atmospheric pressure. The absolute pressure in pressure gauge is equal to the observed gauge pressure plus the atmospheric pressure where as the absolute pressure in vacuum gauge is equal to atmospheric pressure minus the vacuum.

02) Volume: - It is the space which the given substance occupies and it is measured in cubic meters. The most known unit of volume is liter.

The specific volume of a substance is its volume per unit mass and generally expressed in cubic meter per kilogram of air at zero degrees centigrade and under a pressure of 760 mm of mercury has a volume of 0.7734 cubic meters. Therefore, the specific volume of air under this condition is 0.7734 meter cube per kilogram.

The density of substance is its mass per unit volume is generally expressed in kilogram per cubic meter. So, under same conditions of pressure and temperature, if the specific volume of air is 0.7734 meter cube per kilogram then its density is 1.293 kilogram per meter cube.

03) Temperature: - It is the measurement of hotness or degree of coldness of a given substance.

Ordinarily temperatures are measured by thermometers, high temperatures are measured by pyrometers, small and precise changes of temperature can be measured by resistant thermometers and thermocouples.

In centigrade thermometer the freezing point of water is marked as zero and the boiling point as 100 at the atmospheric pressure, these points are called as fixed points of a thermometer.

Absolute zero is the temperature at which the internal energy of a substance becomes zero. The measurement of temperature taken above the absolute zero is known as absolute temperature and expressed in degrees of Kelvin scale or K.

The exact relationship between Kelvin scale and Celsius scale is,

Temperature K = Temperature degree centigrade + 273.15

I hope the above important information will help you to understand about some fundamental properties.

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How to Inspect Steam Boiler by Different Ways?

For power generation through steam turbine or steam engine, steam is required. Steam is also required for industrial process work, hot water supply and heating installations etc. This steam is produced with the help of utility called boiler.

A boiler is a closed vessel where combustion of fuel produces heat to convert water into steam at the desired temperature and pressure.

For the safe operation of boiler, it should be inspected by various methods and at various stages. You will find some important information on boiler inspection from below description.

01) Inspection before registration:-
Every new boiler must get registration from government authority so this is the first inspection carried out on new boiler. For this inspection boiler is completely stripped off all its mountings, coverings etc. Each and every part is carefully examined for defects due to design, workmanship or transportation. If any defects found, these are noted in the registration book.

The working pressure of the boiler is fixed after testing its various parts and a certificate is issued for the results obtained. After various satisfactory tests, the boiler is registered and a registration certificate is issued.

02) Annual Inspection: -
Generally boiler inspection is carried out annually but in case of any accident or abnormal complaint it should be done at any time. In this inspection all parts, mountings and accessories are removed and inspected.

The boiler is inspected from internally and externally for any defects which may develop during the course of its working. If the boiler found defect free then only the certification of registration is renewed.

03) Hydro Test: -
The hydraulic test is carried out to inspect the tightness of joints, fittings and the leakages from the repaired parts. To carry out this test, the boiler is completely filled with pressurized water. The water pressure is different for different situations as below,

01) For an old boiler, the hydraulic pressure applied will be 150% of the prescribed pressure for operation. At the given pressure the boiler should not leak at any spot.

02) For the new boiler,
A) The hydraulic pressure applied will be 200% of the working pressure and it should not leak under this pressure. The pressure mentioned is applied when the boiler has working pressure is less than 100 lbs/inch square.
B) When the boiler is working above 100 lbs/inch square, the hydraulic pressure applied for test is 150% + 50 lbs/inch square and the boiler should not leak at any spot under this pressure.

04) Steam Test:-
To check the setting of the safety valves at the working pressure, this test is carried out. After satisfactory test, the valves are sealed and the owner is not permitted to change the settings.

05) Inspection in Presence of Steam: -
This type of test is very rare but when boiler can not stop due to any reason, this test carried out. At the time of this test, steam generation is in process by boiler. A prior approval is from government is necessary to run the boiler after expiry date of its current certificate.

06) Internal Inspection: -
When boiler is small in size and when inspector can not enter inside for close inspection of internal parts this type of test is carried out. Inspection is done when internal parts are taken out for repairs.

07) Causal Inspection:-
To check out that the boiler owner is operating the boiler according to boiler act, the surprise visits from time to time are carried out for inspection.

08) Accident Inspection: -
If due to any reason accident took place, the boiler inspector holds an inquiry to fix the reasons of accident, the damage to the boiler and worker by inspection at site.

If you know something more on the topic, please add it by comments.

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Various Methods For Compounding of Steam Engines.

For greater efficiency and less space per horse power, high pressure steam is used in steam engine. Now with the use of this high pressure steam the range of expansion is correspondingly increased. If full expansion is takes place in single cylinder the walls of the cylinder to be made very thick to withstand the high pressure and also required a heavy flywheel. All this made a simple steam engine very heavy in construction, large variations of temperature and more leakage past the piston.

To overcome these difficulties, the expansion of steam is made in two or more cylinder. This called as “Compounding the expansion of steam”. There are three different methods of compounding of steam engines as below,

01) Tandem Compounding:-
In this type, the cylinders are arranged on common axis and two pistons have a common piston rod, connecting rod and crankshaft. The exhaust steam from high pressure cylinder passes directly into low pressure cylinder where it further expands.

The turning moment in this type of this type of engine is not uniform due to common crank and piston rod where all the torque acts at the same time. This is the basic disadvantage of such type of engines and requires a large flywheel. Tandem arrangement gives constructional economy because of less components of the engine.

02) Woolf Compounding:-
In this type, two cylinders are arranged side by side while the two cranks are placed at 180 degree to each other. The pistons of high pressure and low pressure cylinders begin and end their strokes together respectively.

The exhaust of steam from high pressure cylinder coincides with suction of steam in low pressure cylinder. In this case also exhaust steam from high pressure cylinder passes directly into low pressure cylinder where it further expands.

Since the two cranks are at 180 degree to each other, the two cycles are in phase and this causes large variation in the turning moment of crankshaft and necessitating the use of heavy flywheel.

03) Receiver Type Compounding:-
In this type, two cranks are mounted at 90 degree to each other that is why steam from high pressure cylinder can not exhaust directly into low pressure cylinder.

A container, known as receiver is used to collect steam from high pressure cylinder while low pressure cylinder draws steam from receiver for further expansion.

The turning moment in receiver type compounding steam is more uniform therefore a lighter flywheel can be used. With three cylinder engine, the cranks are arranged at 120 degree to each other but still small turning moment variation can be achieved.

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What Are The Advantages of Compound Steam Engine?

According to expansion of steam, the engines are classified as simple steam engine, compound or multi expansion steam engines, out of this; compound steam engines have more advantages than simple steam engine. The main advantages are as listed below,

01) Light weight cylinders are required in compound steam engine. The cylinder in simple steam engine is required to make strong and large enough to withstand the high pressure steam and to accommodate the large volume of low pressure steam respectively for the same expansion ratio comparing to compound steam engine.

Compound engines are light in weight as the high pressure cylinder only subjected to maximum pressure, but its diameter is small and low pressure cylinder is large in size but light in weight.

02) Temperature Range means the difference between the highest and lowest temperatures of steam within the cylinders and this range in each cylinder is reduced, with a corresponding reduction in initial cylinder condensation and temperature stresses.

03) In case of breakdown, the engine can be run on a reduced load by using only one cylinder. This feature gives great advantages especially in marine propulsion.

04) A lighter flywheel can be used in modern compound engines because of lower variation of turning moment as the cranks are at 90 degree to each other. This results in better mechanical balance, which allows higher speed of the engine.

05) After expansion in the high pressure cylinder the steam can be reheated before admission to the low pressure cylinder.

06) Because of the reduced pressure difference in each cylinder the leakage of steam past the pistons and valves are reduced.

07) There are less forces acting on the working parts as the forces are distributed over more components of the engine.

08) The compound steam engine may start in any position which is an advantage for locomotive and marine engines.

09) As there are two or more cylinders and pistons in compound steam engine the stroke length of each cylinder is comparatively less than simple steam engine.

10) For same horsepower the cost of the compound steam engine is less than simple steam engine because of lighter parts used in this type of engine.

You can add more advantages to above list by commenting.

How to Classify of Steam Engines in Different Way?

In old days reciprocating steam engines are used to convert heat energy into mechanical energy. Now a day’s steam turbine or internal combustion engines are used for the same work. But steam engine has many specialized applications. These steam engines can be classified according to its construction and operating features. Detail classification is covered as below.

A) Position of Cylinder: - According to the position of the cylinders steam engines can be classified as,
01) Vertical Engine
02) Horizontal Engine
03) Inclined Engine

B) Working Stroke: - Steam Engine is classified according to number of working strokes per revolution as,
01) Single Acting
02) Double Acting

In single acting engine there is only one stroke per revolution of the crankshaft as steam acts on one side of the piston. But in double acting engine two working stroke per revolution are obtained as steam acts on both sides of the piston.

C) Speed of Engine: - According to the running speed of the engine it can be classified as,
01) Low Speed Engine, Where engine runs at 100 or less revolution per minute.
02) Medium Speed Engine, Where engine runs at 110 to 200 revolutions per minute.
03) High Speed Engine, Where engine runs above 200 or more revolution per minute.

D) Field of Application: - Steam engines are classified according to its applications as,
01) Locomotive or Portable Engines
02) Stationary Engines
03) Marine Engines

E) Exhaust of Steam: - Steam engines are classified by exhaust of steam as,
01) Condensing Engines, Where exhaust steam passes into a condenser at lower pressure than atmosphere.
02) Non Condensing Engines, where exhaust steam passes directly to the atmosphere.

F) Governing Methods: - A classification is frequently made according to the governing method employed as,
01) Throttle Governing, in this method the speed of engine is controlled by means of valve in the steam pipe which regulates the pressure of the steam entering the engine.
02) Automatic Cut-Off Governing, in this method governor controls the quantity of steam admitted to the cylinder while the pressure of entering steam is remain constant.

G) Expansion of Steam: - Steam engines are classified according to expansion of steam in number of stages as,
01) Simple Steam Engine, where conversion of heat energy of steam into mechanical work in one stage only with one cylinder and piston.
02) Compound Steam Engine, where the conversion of heat energy of steam into mechanical work occurs in two stages with high pressure and low pressure cylinder.
03) Triple Expansion Steam Engine, where the steam expands successively in three cylinders.
04) Quadruple Expansion Steam Engine, where four cylinders and pistons are used for expansion of steam.

Besides above classification, steam engine can also be classified according its length of working stroke i.e. short stroke or long stroke engines and position of crank i.e. side crank or centre crank engines.

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What Are The Essential Qualities of Good Lubricant?

To reduce the frictional losses between metal to metal rubbing or sliding parts, lubrication is required. Below are the some essential qualities of a good engineering lubricant.

01) Viscosity: - When any lubricant offered resistance to the deforming forces, it is called viscosity of the lubricant. Good quality lubrication oil must maintain sufficient viscosity at higher temperatures and it should not be too viscous at lower temperatures.

For high speeds, low viscosity lubricants are suggested while for large clearance and high loads; high viscosity lubrication oil is recommended. The viscosity of oil increases, if the temperature of mating surfaces decreases.

02) Flash & Fire Point: - Flash point of the lubrication oil is the minimum temperature at which it gives off enough vapour to form a momentary flash when naked flame is brought near its surface, while the fire point is the lowest temperature of the lubrication oil, where it burns continuously. To avoid the possibility of fire, the flash point of oil must be higher than the temperatures likely to be developed in the rubbing surfaces.

The fire point is generally higher than the flash point and the difference between flash point and fire point must be 18 degree centigrade at higher side.

03) Oiliness: - It is the property of lubrication oil to spread and attach itself firmly to the lubricating surfaces. When mating surfaces are subjected to a high intensity of pressure, it is recommended to particularly high oiliness; so that the metal is protected by a layer of oil and the wear is reduced.

04) Volatility: - Lubrication oil losses a certain weight due to evaporation when it is subjected to high temperature for long hours. This loss is known as “loss by evaporation”. The consumption of oil is considerably increased with high volatility at normal working temperatures that is why low volatility is always suggested for lubrication oil.

05) Stability & Insoluble Residue: - Stability of oil is to resist oxidation that would yield acids and sludge. Good lubrication oil must have high stability.

Free carbon or hydrocarbons decomposing into carbon at high temperature is called as insoluble residue. Good quality lubrication oil should not have any insoluble residue.

I hope the information above will help you to select proper lubricants for your machines.

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