584 



HYDRAULICS AND ITS APPLICATIONS 



the bucket rod works, the machine becomes a force pump for delivering 

 water under pressure (Fig. 269). The provision of a back pressure valve 

 on the delivery side of the pump is now necessary to prevent the back- 

 ward escape of the water on the down or idle stroke. As thus arranged 

 the pump may be either vertical or horizontal. 



As pressures are increased, the bucket type of pump is found to be 

 unsatisfactory on account of the difficulty in keeping the bucket and its 

 valves tight and of detecting any leakage, and this led to the adoption of 

 the Plunger Pump (Fig. 270). Here the bucket is replaced by a plunger of 



FIG. 271. Steam Driven Single-acting Plunger Pump. 



uniform section, all the packing being supplied from the outside am 

 being easily replaced and examined. In this type of pump, which may be 

 either vertical or horizontal, work is done on both strokes, suction taking 

 place on the out-stroke of the plunger, and delivery by plunger displace- 

 ment on the in-stroke. The latter in general necessitates the greater 



