HUMPHREY INTERNAL-COMBUSTION PUMP 261 



which exists in the suction tank. When the kinetic energy of 

 the moving column has been expended in forcing water into the 

 water tower, it comes to rest and as there is nothing to prevent 

 a return flow, the column starts to move back towards the 

 pump, gaining velocity until the water reaches the level of the 

 exhaust valve, which it shuts by impact. A certain quantity 

 of burnt products is now imprisoned in the cushion space f and 

 the energy of the moving column is expended in compressing 

 this gas cushion to a greater pressure than that due to the static 

 head of the water in water tower wt. Hence a second outward 

 movement of the column is produced and when the water 

 reaches the level of valve e the pressure in the space f is again 

 atmospheric ; further movement of the water opens valve a 

 against a light spring and draws in a fresh charge of gas and 

 air. If there were no friction, the water would fall to the same 

 level as that from which the last upward motion started but the 

 amount of combustible charge drawn in is slightly less than this 

 movement would represent. Once more the column of water 

 returns under the pressure due to its elevation and compresses 

 the charge of gas and air, which is then ignited to start a fresh 

 cycle of operations. 



The ignition is timed by a small apparatus somewhat re- 

 sembling an ordinary engine indicator which closes the electric 

 ignition circuit at the point of maximum compression ; it is 

 effected by an ordinary small battery, trembler coil and sparking 

 plug such as are used in motor-car work. 



It should be noticed that the only moving parts, namely, 

 the valves, open and shut under slight changes in pressure 

 and are all on their seats when explosion occurs ; consequently, 

 there is no shock and the pump works quietly and smoothly. 



In starting the pump for the first time, compressed air is 

 allowed to flow into the combustion chamber until the volume 

 of air introduced is rather larger than the usual charge. The 

 exhaust valve is then suddenly opened by means of a hand 

 lever and the escape of the compressed air permits a movement 

 of the water column which gives the cushion and suction 

 strokes and so draws in a fresh combustible charge, which, 

 on ignition, starts the pump working regularly. If the pump 

 is stopped when in regular work, it always stops with a fresh 

 charge of gas and air in the combustion chamber ; the re- 

 Starting of the pump is simply effected by switching on the 



