692 



HYDRAULICS AND ITS APPLICATIONS 



The engine is stopped and started by the bar N, which, when held 

 against the pendulum, engages with the rachet M when this begins to 

 descend. This stopping takes place immediately before the end of a 

 working stroke, when the main valve is closed and when the flow of water 

 in the main pump has for the moment ceased. On releasing the rachet, 

 the ram at once engages on a normal stroke. 



As thus constructed, the machine is capable of dealing with practically 

 any quantity of water, and works as noiselessly as a pumping engine. 

 The smoothness of its working as compared with that of the ordinary 

 type of ram may be inferred from Fig. 336, which shows a diagram taken 

 from the valve box of a ram of this type. 



The simplicity of the mechanism of the hydraulic ram, its high 



Mean Pressure in A ir Vessel 



Pressure Due to Delivery Head 



Atmos. ^* 



FiG. 336. Pressure Diagram from PearsalFs Hydraulic Ram. 



efficiency, and the fact that it is capable of working for very long periods 

 without attention, render it specially well fitted for use in a private 

 pumping plant, and there is every indication that at the present time its 

 many advantages are being to an increasing extent realized. 



Hydraulic Earn for Air Compression. With slight modifications the 

 hydraulic ram maybe adapted for use as an air compressor. Thus in the 

 Pearsall ram the chamber E is enlarged so as to hold the whole volume 

 of air compressed in a single stroke, while the valve at F is modified so 

 as to confine this air, and the delivery valves at G are slightly modified. 

 The cylinder P is also now worked by pressure water from the air vessel 

 E instead of by compressed air. As thus constructed, efficiencies oi 

 upwards of 80 per cent, may be obtained. 



Fig. 337 shows a type of air compressor on somewhat similar lin( 



