748 



HYDRAULICS AND ITS APPLICATIONS 



In the second method, the lower side of 

 the plunger is in free communication with 

 an open standpipe of height h feet contain- 

 ing water. Let d and D be the diameter of 

 standpipe and of plunger, in feet. Then 



R D 2 



if h = . , the difference of upward 

 m d* 



pressure on the plunger at the top and 



bottom of its stroke is 62'4 - - ( h + ) 



4 \ m) 



Ibs. 



For this difference of pressure to counter- 

 balance the difference in the effective weight 



of cable, i.e., wE (1 -j- ), we must have 



w 



' h ~ m I 62-4 



(m + I) 





while 



D 



62-4 



The suspension system has certain advan- 

 tages in virtue of the cheapness of construc- 

 tion of the shorter ram and cylinder, and 

 does not necessitate the provision of a deep 

 well below the lift shaft to contain the 

 cylinder, which may be fixed horizontally if 

 required. Its drawbacks are due to the 

 inefficiency of the multiplying jigger, and to 

 the serious effects which may follow the 

 rupture of a wire rope. If carefully designed, 

 and frequently examined, the latter con- 

 tingency should, however, be very remote, 



FIG. 364. Multiple Wire Sus- while the provision of adequate safety catches 



and brakes renders this almost as safe as the 

 direct-acting system^ The speed of hoisting 

 may be made as great as is convenient. For passenger hoists this is 

 usually about 2 feet per second, and for warehouse hoists up to about 



pended Lift with 

 balance Weights. 



