ACCUMULATORS 



723 



tates may be avoided by the provision, in the place of the relief valve, of 

 a spring-loaded plunger, in which case the kinetic energy of the moving 

 ram is expended in compressing the spring. 



Its inertia is, however, an advantage in some cases, as, for example, 

 where fitted to a hydraulic riveter or similar machine. Here the inertia 

 is utilized to increase the pressure at the end of the stroke, the final and 

 sudden impact thus produced causing the rivet to fill up its hole effectively. 



Fig. 346A. shows a spring loaded plunger with relief valve arranged to 

 open when the rise in pressure exceeds a certain limit. The necessary 

 dimensions of this may be calculated when the size of accumulator and 

 circumstances involved in its use 

 are known. If, for example, the 

 weight of accumulator ram and 

 load is 160 tons ; the maximum 

 velocity of fall 10 ft. per minute 

 = *166 ft. per second ; the dia- 

 meter of ram 9 inches ; the normal 

 working pressure 2'5 tons per 

 square inch ; the energy of the 

 falling weight to be absorbed by 

 the spring loaded plunger with a 

 10 per cent increase in pressure. 



Kinetic energy of falling weight 

 160 



= -069 ft. tons. 



To Motor 



From Accumulatot'i 



FIG. 346A. 



36 X 64-4 



To absorb this amount of energy 

 the ram must fall through a further distance x feet, against the excess 

 resistance due to this increase in pressure, and as the mean excess 

 resistance is 5 per cent, of 2'5 tons per square inch we have 



81 1 X x = '069 



125 X 



. . x = '0087 feet = 104 inches. 

 . . vol. of water displaced while coming to rest 



= '104 X ~ = 6'61 cub. in. 

 4 



Making the plunger of the valve 2 inches diameter, the spring would 

 require to be so designed as to allow of a displacement of 



= 2*1 inches under an increase of pressure from 2'5 to 2'75 tons per 

 square inch. With any greater displacement the under side of the 

 plunger would engage with and would lift the small escape valve V. 



3 A 2 



