L>1 5 STEAM EXC.IXES 



taper, or both, on one side of the crosshead and a nut on the 

 other; or the rod may be secured to the crosshead by a cotter, 

 instead of the nut; or the end of the rod may be threaded and 

 screwed into the crosshead, having a check-nut to hold the rod 

 in place. In the case first mentioned, the nut may work 

 loose, which would cause the crosshead to receive a violent 

 blow, first, by the nut on one side and then by the shoulder 

 or taper on the other at each change of motion of the piston. 

 The remedy is to set up the nut. A similar effect will be 

 produced if the cotter should work loose and back out. In 

 case the piston rod is screwed into the crosihead and the rod 

 slacks back, the danger is that the piston will strike the rear 

 cylinder head. The check-nut should be closely watched. 

 Pounding at the crosshead may be due to loose wristpin brasses, 

 in which case they should be set up, but not too tightly. In 

 case a crosshead works between parallel guides, pounding may 

 be caused if the crosshead is too loose between the guides, 

 and the crosshead shoes should therefore be set out. 



If pounding results from the wearing down of the shoe of 

 a slipper crosshead, a liner should be put between the shoe and 

 the foot of the crosshead or the shoe should be set out by the 

 adjustment provided. 



Pounding in Air Pump. Pounding in the air pump is gener- 

 ally produced by the slamming of the valves, caused by an 

 undue amount of water in the pump, which will usually relieve 

 itself after a few strokes. The pump piston, however, may 

 be loose on the piston rod or the piston rod may be loose in 

 the crosshead. A broken valve may also cause pounding in 

 the air pump, all of which must be repaired as soon as detected. 



Pounding in Circulating Pump. In a circulating pump of 

 the reciprocating type, pounding may be caused by admitting 

 too little injection water, and the pounding n:ay be stopped 

 by adjusting the injection valve to admit just the right quantity. 

 It may so happen, however, that the injection water is very 

 cold, and to admit enough of it to stop the pounding in the 

 circulating pump will make the feedwater too cold. To 

 meet this contingency, an air check-valve is often fitted to the 

 circulating pump to admit air into the barrel of the pump as 

 a cushion for the piston; this check- valve may be kept closed 



