2O SCIENCE OF SUCCESSFUL THRESHING. 



at which it once worked well. This indicates that the pas- 

 sage-ways in jets are either worn or are contracted with lime. 

 If removing the lime does not remedy the trouble, the over- 

 flow valve may leak. To regrind it, remove cap "Z" and 

 spread a little flour of emery, mixed with oil or soap, between 

 the valve "P" and its seat. Then with a screw driver, turn 

 valve "P" back and forth, which will grind it to a seat. If 

 the injector be not improved, it is safe to conclude that some 

 of the jets are worn and must be renewed. These are sold 

 separately, and are listed in threshermen's supply catalogs. 

 If in doubt as to which jet is at fault, procure all of them and 

 try one after another until the injector works properly. Any 

 unused jets may be returned. 



Independent Pumps. This is the name given to pumps 

 for feeding a boiler, which are operated independently of the 

 engine. They are, in fact, small engines in themselves, con- 

 nected directly to double-acting pump plungers. An inde- 

 pendent pump can be run whether the engine is running or 

 not, but as the heater is effective only when the engine is 

 running, it is best, on boilers having both pump and injector 

 to use the injector when the engine is not running. The 

 Marsh pump has an exhaust valve for turning the exhaust 

 of the pump in with the feed water. This, of course, heats 

 the feed water and renders the pump more economical. If, 

 for any reason, it is desired to use the pump when the engine 

 is not running, the exhaust should be turned in, to prevent 

 putting cold water into the boiler. At other times, however, 



