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,

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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