714 HYDRAULICS AND ITS APPLICATIONS 



wells, and as it is essential that all deposit should be removed before use, 

 it is allowed to stand for some time in storage tanks. The greater part 

 of the solid matter is deposited here, and the water is then passed through 

 the surface condensers of the engines to a series of niters, in which it is 

 passed first through a layer of broken sponge 18 inches thick, and after- 

 wards through a bed of charcoal. After leaving the filters it is pumped 

 into the clean water tank, from which the main pumps derive their 

 supply. 



Among other advantages of hydraulic transmission it may be noted that 

 power is always immediately available ; that gearing in the machine 

 is 'in general unnecessary, the force being transmitted directly from the 

 hydraulic piston ; that perfect regulation is easy ; that when applied 

 to the direct working of lifts and of hoists a brake is unnecessary, and 

 that so long as the velocity of flow is kept low the transmission losses are 

 small with well designed pipe lines this loss should not exceed 10 Ibs. 

 per square inch per mile. 



As compared with electric transmission, it has the advantage that 

 fire risks are eliminated, while for slowly moving machinery, inter- 

 mediate gearing is largely eliminated. Compared with transmission 

 by compressed air, it has the advantage that any leakage is easily 

 detected, while under suitable conditions the hydraulic transmission 

 losses are much the lesser. Each of the three systems of course has 

 its own particular sphere of application. For long-distance work the 

 necessary cost of, and losses in the pipe line, would effectively militate 

 against the application of hydraulic transmission, and a radius of 15 

 miles from the central station would appear to mark the limit of its 

 effective use. 



The various losses occur 



(1) At the power station roughly about 15 per cent. ; 



(2) In transmission about 5 per cent. ; 



(3) In use about 8 per cent. ; 



leaving a percentage to be utilized of about 72 per cent. 



The last two items, however, vary considerably with the type of 

 machinery, and the energy utilized may vary from 30 to 95 per cent., 

 the latter percentage being obtained with such machines as direct acting 

 coal shoots, where the load, during its descent, may be made to pump 

 pressure water back into the mains. 



Losses. The losses at the power station are those incidental to the use 

 of reciprocating pumps and accumulators, and are considered in detail in 

 that connection. 



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