28 



SCIENCE OF SUCCESSFUL, THRESHING 



holes at each end are wholly unobstructed at their points 

 of register with the corresponding holes in the chest. The 

 packing under the valve plate must be patterned from the 

 faced top of water cylinder, and the packing over the valve 

 plate from the bottom face of the air chamber. The steam 

 cylinder head must not be packed with anything thicker 

 than heavy paper or the thinnest rubber. If a thick gasket 

 be used, the piston will overrun the ports, and its operation 

 be interfered with. 



Check-Valves. A check-valve allows the water or 

 other fluid to flow in one direction, by the valve rising 

 from its seat, but when water attempts to "back up," or 



flow in the opposite direction, 

 the valve prevents this by 

 closing. With any style of 

 boiler- feeder, a check- valve 

 is placed in the feed-pipe, 

 and usually near the boiler. 

 Between the check-valve and 

 boiler is placed a globe or an- 

 gle valve which may be 



closed, allowing the check 



FIG. 6. SECTION OF CHECK VALVE. 



valve to be opened when the 



boiler is under steam pressure. If the pump or injector 

 shows, by heat or other indications, that water and steam 

 are "backing up" through the feed pipes from the boiler, 

 it indicates that the check-valve is not acting. When the 



