AIR COMPRESSORS 39 



maintained for any considerable time, as even this speed will 

 cause excessive heating. This is shown by another test where 

 an average speed of about 60 exhausts per min., after the main- 

 reservoir pressure was pumped up, and a maximum of 77 strokes 

 per min. at the completion of 1 hr. and 50 min. of the test, 

 gave a discharge temperature of 316. The foregoing show 

 plainly the great need of good maintenance, of not wasting 

 air either by leakage or poor handling, and of giving the com- 

 pressor as much time to do its work as is practicable. 



With two compressors per engine, the separate throttles 

 should be kept wide open and the speed regulated by the main 

 compressor throttle, in order to divide the work equally 

 between the two compressors. 



Compressor Faults. It is evident that a compressor can- 

 not compress more air than it draws in and not that much if 

 there is any leakage to the atmosphere about the air cylinder. 

 Bearing this in mind, practice frequently listening at the air 

 inlet when the compressor is working slowly while being con- 

 trolled by the governor, and wherever a poor suction is noted 

 on either or both strokes locate and report the fault. One of 

 the most serious leaks is through the air-cylinder stumngbox, 

 as it not only greatly decreases the air delivered, and, by 

 the faster speed required, increases the heating, but it also 

 causes pounding through loss of cushion. When tightening 

 the packing, do not bind the rod, as to do so will damage 

 both the packing and the rod. Be careful not to cross the 

 gland nut threads. 



If necessary to replace a broken air valve on the road or 

 elsewhere, not permitting of proper fitting, at the earliest 

 opportunity have the repairman replace the temporary valve 

 with another so as to insure the correct angle and width of 

 valve and seat 'contact, the needed ground joint and the requi- 

 site lift for all valves. 



Never remove or replace the upper steam-cylinder head with 

 the reversing-valve rod in place as to do so will almost invari- 

 ably result in bending the rod and causing a pump failure. 



Any unusual click or pound should be reported as it may 

 indicate either a loose piston or a reversing-valve plate cap- 

 screw or other serious fault. 



