26 SCIENCE OF SUCCESSFUL THRESHING. 



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 valve "sticks" and will not close, a very slight tap may 

 cause it to "seat," but if this does not, close the valve be- 

 tween it and boiler, then take off the cap and remove dirt 

 or scale that may be preventing it from closing tightly. If 

 no foreign matter be found, examine the valve and seat to 

 determine if the contact surfaces be perfect. If scale be 

 found adhering to either, it should be removed, but if it be 

 "pitted," regrinding is necessary. Although a slight tap 

 will often cause a check-valve to seat, it is poor practice to 

 constantly or violently hammer the valve, as the seat may be 

 distorted, and the entire valve ruined thereby. Many valves 

 are also distorted and ruined because a wrench has been used 

 on one end while screwing a pipe into the other. Many 

 valves are burst during cold weather by frost. To prevent 

 this, the angle valve near boiler must be closed and the 

 check-valve and pipe drained. 



Regrinding Check-Valves. Many engineers discard .leaky 

 valves as worthless, in ignorance of the ease with which 

 they may be re-ground. The swing check is easily re-ground 

 without disconnecting it from the pipe. To regrind, unscrew 

 angle plug, put a little flour of emery, mixed with oil or 

 soap, on the bottom of valve and turn it back and forth 

 with a screw driver until the contact surfaces are perfect. 



