Steam Engines. 515 



If a soft plug blows out in the field it may be tem- 

 porarily refilled with lead or Babbitt metal but the melt- 

 ing point of these is too high to prevent the plate from 

 being injured. The soft metal is an alloy made by melting 

 together equal weights of lead and tin, having a melting 

 point of 420 F., that of lead being 610 and Babbitt 

 metal 650 F. 



646. Water Supply. The water supply to the boiler 

 must always be adequate and under complete control. 

 The greatest care and vigilance should be exercised by 

 the engineer and he should know that his pump and in- 

 jector are in prime condition at all times. In the first 

 place the cleanest water which can be had should always 

 be used and if necessary the water should be strained when 

 it is put into the supply tank. Be sure that the suction 

 hose and connections are free from leaks. It sometimes 

 happens that the nipples screwed into the boiler through 

 which the injector and pump feed, lime up and these 

 should be examined occasionally to see that they are free. 



There are two methods of supplying the boiler with 

 water (1) with a pump and (2) with an injector. Pumps 

 are either driven by the engine when that is running or 

 directly by steam pressure. 



647. Cross-head Pump. A common form of pump for 

 supplying the boiler with water is known as the cross- 

 head because it is driven from the cross-head of the engine. 

 This being true it is of course only available when the 

 engine is running and an engine with this sort of pump 

 should also be provided with an injector. 



The independent boiler feed pumps are some one of the 

 stonin types and are practically small steam engines which 

 drive the pump cylinder. 



648. The Injector. The principle by which steam from 

 the boiler is able to force water back into the same boiler 

 against the same pressure and the action of the injector 



