BOILERS AND GENERATION OF STEAM 315 



The steam pump is commonly used in power plants ,to 

 supply feed water to the boiler. It is very important for 

 the engineer in charge of the plant to see that the pumps 

 supplying the steam boilers are in first-class order at all 

 times, as any failure to maintain the water at a proper level 

 in the boilers may result in serious injury to the boilers; an 

 explosion may even occur. 



One end of a boiler pump is called the engine or steam end 

 and the other the pump or water end. A boiler-feeder is 

 intended to feed water into steam boilers while they are under 

 pressure. To illustrate: If the boiler is under a pressure of 

 100 Ibs. to the square inch, and the steam piston in the pump 

 receives 100 Ibs. to the square inch, it is clear that there will 

 be equilibrium between the steam pressure and water pres- 

 sure of the pump. This is overcome by reducing the plunger 

 diameter to perhaps one-half the size of the steam piston. 

 In this way an unequal area in the steam piston and pump 

 plunger is obtained. This difference enables the pump to 

 force water against a pressure greater than that of the 

 boiler. The necessary allowance for friction varies from 

 5 to 40%. 



When a pump takes in water at only one end of the piston, 

 it is called a single-action pump ; when it takes water in at 

 both ends, it is called a double-action pump. 



All single, direct-acting pumps make use of an auxiliary 

 plunger to carry a valve which gives steam to the main pis- 

 ton. By means of various devices, steam pressure is made to 

 drive this auxiliary plunger backward and forward. 



356. Measurement of Pump Pressure and Capacity. 



The formula for lifting or forcing water either under pressure 

 or head is as follows : P = HA W. 



