HYDRAULIC POWER TRANSMISSION 

 The efficiency of transmission is then given by : 



717 



Also 



_ H.P. X 550 



Xa 

 55,000 X 4 



f.s. 



750 X TT X 144 X '2642 

 = 2*45 feet per second. 



If p = 1,120, then for the same fall in pressure per mile we have, for 

 100 H.P. : 



d = '4377 feet = 5*25 inches 

 while v = 2'27 feet per second. 



The following table then gives the efficiency for various lengths of pipe 

 line : 



The velocity of flow through the pipe should not exceed 4 feet per 

 second, velocities ranging from 2*5 to 4'0 feet per second being usual. 



While an increase in the working pressure increases the efficiency of 

 transmission, it also necessitates an increase in the thickness of the pipe 

 walls, which counterbalances the advantages of the reduced internal 

 diameter. Also the difficulty of preventing leakage at joints increases 

 with the pressure, so that in practice it has not been found advisable to 

 adopt pressures much in excess of 1,100 Ibs. per square inch. 



Losses in Use. These are due partly to friction, but, in the majority of 

 hydraulic machines, more particularly to shock at sudden changes of 

 section in valve boxes and supply ports and pipes, and to the necessity in 

 many machines for filling the inlet passages with pressure water before 

 the commencement of each working stroke. The latter loss may be 

 prevented by having separate inlet and outlet passages to the working 



