WATER-RRESSUUE PUMPS.

pair acting conversely. The water is forced into an air vessel,and thence through the rising main in. one lift to the surface,the power supplied by the descent of water in one column beingnearly sufficient to effect its return in the other. The tubeswere proved to 100 atmospheres. The working pressure on theUnderground pumps (due to the difference between their areasand those of the pumps at the surface) is 50 atmospheres, andthe hydrostatic head in the rods is 27 atmospheres. The totalworking pressure, including friction, is 77 atmospheres, or about1155 Ibs. per square inch. The engine is worked at a speed of10 double strokes per minute, the delivery of water being con-tinuous. Careful observations were made in order to ascertainthe work absorbed by the friction of the different parts of themachinery, and it was found to be from 25 to 29 per Cent, of thetotal power developed. The effective work of the pumps, at 10double strokes per minute, was 100 HP, and the indicated HPof the engine, with a mean pressure of 20 lbs. per square inchon the piston, was 136 HP, which gives a combined efficiencyof 75 per cent.

Where small heads of water of 70 feet or so have to beutilised, and where the power is required continuously, a water-wheel or turbine possesses advantages over an hydraulic engine,which it is necessary to make large and eumbersome. If highspeed is required, then a turbine might be used even with agreater head, as the speed involved by applying high pressurewater to a turbine is not a disadvantage. The skin friction,which is so important a factor in turbines, is reduced to a mini-mum where they are small and work at high speeds. If a slowmotion, on the other hand, is wanted, and a high pressure ofwater has to be utilised, the power had better be applied to adirect-acting pump. A large turbine working slowly under agreat head would involve serious loss from skin friction in theturbine itself, as well as from friction in the gearing whichwould be required.

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