626 



HYDKAULICS AND ITS APPLICATIONS 



retardation of the suction column may produce a direct flow into the 

 vessel, without the intervention of any acute bends or contracted 

 passages. 



Precisely the same reasoning applies to the delivery air vessel, and 

 here again, for efficient working, the water-level should be adjusted by 

 adjusting the air pressure, until as low as is consistent with water 

 remaining in the vessel throughout the whole cycle. 



ART. 169. AIR-CHARGING DEVICES. 

 One of the simplest devices for maintaining the level in an air vessel is 



the air injector of Messrs. Wippermann and Lewis. In this apparatus, 



which is represented diagrammatically in 

 Fig. 299, the small cylindrical chamber A 

 is connected to the pump barrel by means 

 of a small pipe with regulating cock, and 

 at its upper end carries a valve-box B con- 

 taining air inlet and outlet valves, which 

 is in turn connected to the air space of the 

 air vessel V. 



On the suction stroke in the main 

 pump this chamber is partially emptied, 

 the air is drawn in through the inlet 

 valve. On the delivery stroke of the pump, 

 water is forced into the chamber A and its 

 contained air is driven through its outlet 

 valve into the air vessel V. 



The amount of water entering and leaving 

 A per cycle, and therefore the air enter- 

 ing V, may be accurately adjusted by means 

 of the regulating cock C. 



Another simple device consists of a small 



FIG. 299.-Wi^Sn Air injector, compound air pump, worked by the 



pump shaft, which draws air out of the 



suction chamber, where it tends to accumulate, and pumps it into the 



delivery chamber. 



ART. 170. EFFICIENCY OF THE KECIPROCATING PUMP. 



When dealing with considerable pressures, the reciprocating pump if 



well designed and working at a fairly slow speed is capable of an efficiency 



of up to about 90 per cent. 



