THE HUMPHREY GAS PUMP 709 



pressure in F falls to atmospheric. At this instant the inlet valves are 

 opened, and the further motion of the column draws in a fresh charge of 

 air and gas. Again the column returns under the elevated tank pressure 

 compressing this charge which is then ignited to start a fresh cycle of 

 operations. The cycle is thus identical with that of the four-cycle gas 

 engine. By a comparatively simple modification of the combustion 

 chamber and its valves the cycle may, however, be made to correspond 

 with the two-cycle engine. 1 



EXAMPLES. 



(1) A hydraulic ram uses 50 gallons of water per minute under a supply 

 head of 4 feet, and pumps 5 gallons of this against an effective head of 

 80 feet. Determine the efficiency of the ram. 



Answer. 72'25 per cent. 



(2) A ram uses 900 gallons of water per minute under 10 feet head, 

 and pumps 50 gallons of this through 500 feet of 2^-inch piping into a 

 reservoir at a height of 80 feet above the ram. Determine the efficiency, 

 taking / = '014. 



Answer. 60 per cent. 



(3) The waste valve of a hydraulic ram is 4 inches diameter and is 

 required to begin to close when the velocity of flow past the valve itself 

 is 6 feet per second. Assuming the dynamic pressure on the valve per 



W v 2 

 unit area to be given by T35 - Ibs., where W= weight per cubic foot 



* 9 

 of water, determine the necessary weight of the valve. 



Answer. "328 Ibs. per square inch. 

 Total weight = 4'12 Ibs. 



(4) A jet pump placed 8 feet above the suction reservoir and 60 feet 

 below the supply reservoir, lifts its water through a total height of 

 8 feet 9 inches. Determine its efficiency when delivering 100 gallons per 

 minute and when using 36*5 gallons per minute from the supply reservoir. 



Answer. '257. 



(5) An injector hydrant takes 25*2 gallons per minute of high pressure 

 water at 700 Ibs. per square inch and delivers 150 gallons per minute at 

 a pressure of 65 Ibs. per square inch, the low pressure supply being at 

 30 Ibs. per square inch. Determine the efficiency. 



Answer. *273. 



1 Details of the mechanical construction of these pumps are given in Proceedings Institute 

 Mechanical Engineers, 1909, p. 1075. A set of five recently constructed for the Metropolitan 

 Water Board pump 180 millions of gallons per day, with a lift of 25 to 30 feet. 



