RECIPROCATING PUMPS 



597 



usually noisy and troublesome, and which, under the most favourable 

 circumstances, in a pump of this size, would reduce the efficiency by from 

 3 per cent, to 4 per cent. 



For very high speeds, however, the automatic valve, even though well 

 designed, becomes unsatisfactory, and mechanically operated valves are 

 necessary. 



By their substitution uncertainty as to the exact time of closing is 

 avoided, more uniform closing is effected with less accompanying shock, 

 and by this means, and by careful design of the valves, the speed has been 

 increased until piston velocities of 600 feet per minute at 300 revolutions 

 per minute are now easily obtained with almost entire absence of shock 



Discharge 



FIG. 284. Riedler Express Pump 



This increase in speed permits of the pump dimensions being reduced for 

 the same duty ; gives a smaller delivery per stroke, and hence reduces the 

 liability to shock ; while the possibility of a more uniform flow in both 

 supply and discharge pipes tends to the same end. 



Fig. 284 shows the construction of the pump barrels, rams and valves 

 of a type of high-speed pump designed by Professor Riedler, this particular 

 pump being designed to deliver 375 gallons per minute against a head of 

 500 feet. It is a two-throw pump having rams 6| inches diameter by 

 9 inches stroke ; running at 200 revolutions per minute and driven by an 

 electric motor of 75 B.H.P. running at 500 revolutions per minute. 



The outer end A of the working cylinder B forms the seating of the 

 delivery valve, which consists of two annular brass rings, Ci and C 2 , let 



