720 



HYDEAULICS AND ITS APPLICATIONS 



more water than the motors require the ram rises, and on reaching 

 the upper limit of its travel moves a stop which, by suitable link 

 connection, causes steam to be shut off from the pumping engines. 

 When the ram falls steam is again admitted to the engines, and so on. 



Various modifications of this 

 type have been adopted, the ram 

 in some cases being inverted, 

 fixed and fitted with suitable 

 inlet and outlet orifices, and 

 the loaded cylinder moving 

 vertically. 



The differential accumulator 

 of Mr. Tweddell may also be 

 noted. As indicated in the 

 sketch (Fig. 345), this consists 

 of a fixed ram of area A, sur- 

 rounded over the lower portion 

 of its length by a closely fitting 

 bush of area a. 



This bush terminates below 

 the inlet and outlet holes. The 

 ram passes through both ends 

 of the storage cylinder, through 

 glands of area (A + a) and A, 

 and the effective cylinder area 

 exposed to upward pressure 

 is a. 



Thus p a = W, and by 

 making the bush of small 

 thickness, a very large pres- 

 sure may be maintained by a comparatively small weight. 



EXAMPLE. 



If the ram diameter = 6 inches and the bush is Jinch thick, we have 

 a = 4'91 square inches. 



.*. If p = 1,120 Ibs. per square inch, 



W = p a = 1,120 X 4-91 = 5,500 Ibs. 



Since the storage of energy is only small, this type of accumulator is 

 more suitable for use with single machines of the riveter type. 

 On board ship, and especially for naval purposes, the use of hydraulic 



FIG. 345. Tweddell's Differential Accumulator. 



