THE HYDRAULIC RAM 



691 



falls at each beat. The action may be regulated with considerable nicety 

 by the provision of a regulating valve on this secondary supply pipe. 



It was not until the invention of the hydraulic engine of Mr. Pearsall 

 that the ram attained its highest development and became a really 

 efficient machine for successfully handling large volumes of water. In 

 general terms, this only differs from the ordinary ram in that its valve 

 is opened and closed by mechanical means, this enabling a cylindrical 

 balanced valve to be used, and the periods of the various portions of a 

 cycle to be regulated to suit any given conditions of working. 



Fig. 335 shows the general arrange- 

 ment of the machine. Here A is the 

 supply pipe and B the cylindrical waste 

 valve, which is operated by the valve 

 rod D, and which allows water to escape 

 by the ports C. On closing this valve 

 water enters the chamber E without 

 shock and drives out before it the con- 

 tained air, through a valve regulated 

 by the wooden float F. When the 

 water reaches a certain height the valve 

 at F closes, and the pressure in E rises 

 until sufficient to lift the delivery valves 

 at (T. The small remaining volume of 

 compressed air and the water then 

 enter the air vessel H, from which the 

 water is led away along the delivery 

 pipe T. A second air chamber S is 

 sometimes fitted, but is not essential. 

 The valve B is now opened, the rush 

 of water out of E and down the supply pipe is followed by its closure, 

 and the cycle of operations is repeated as before. 



The method of working this valve is ingenious. The shaft J carries a 

 pendulum K, which swings through an arc of about 240, and also a cam 

 so proportioned as to divide the time of a swing of the pendulum into 

 two parts suitable for the flow and delivery parts of the cycle. This cam 

 regulates the motion of the valve rod. 



In order to maintain the swing of the pendulum against friction, a 

 crank on J is coupled to a piston in the small single-acting cylinder P, 

 into which air is admitted from the air vessel at each double stroke, so as 

 to give a slight impetus to the pendulum at the middle of its swing. 



FIG. 335. Pearsall's Hydraulic Engine 

 or Ram. 



