THE INJECTOR HYDRANT 



699 



give a stream about 50 feet high, the same when reinforced by a f-inch 

 jet of water at 750 Ibs. per square inch will lift a slightly greater (about 

 15 per cent.) volume of water from the main and will deliver this as a jet 

 85 feet high. 



The efficiency of the hydrant from an energy point of view ranges from 

 28 per cent, to 33 per cent. 



The following table, given by Mr. Greathead 1 , shows the quantity 

 of high pressure water, at 700 Ibs. per square inch, required to deliver a 

 jet of 150 gallons per minute through a 1-inch nozzle, through a height 

 variously estimated to be from 75 to 84 feet, and requiring a head at the 

 nozzle of 100 feet. Here allowance is made for 200 feet of 2J-inoh hose, 

 the resistance of which is equivalent to 50 feet head. 



ART. 189. THE AIR LIFT PUMP. 



Among other devices for pumping liquids against a large head, that 

 known as the air lift pump is worthy of notice. Invented probably by 

 Carl Loscher about 1797, the system fell into comparative desuetude for 

 many years, and has only recently been revived and improved. In view 

 of its increasing use, and of its adaptability to many difficult cases of 

 pumping, it is worth while considering the system somewhat in detail. 

 Briefly, the method consists in sinking an open vertical pipe with its 

 lower end submerged in the liquid to be raised, and having its upper end 

 arranged to discharge into a reservoir at the required height. Air from 

 a compressor is then forced through a smaller air pipe into the submerged 

 opening of the lift pipe or rising main. The air bubbles, rising through 

 the water in the lift tube, so reduce the specific gravity of the mixture, 

 and therefore the weight of the column, that the excess pressure at the 



1 " Proceedings Institute Mechanical Engineers," 1879, p. 364. 



