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HYDRAULICS AND ITS APPLICATIONS 



The Allen press works on a very ingonious principle and is illustrated 

 diagrammatically in Fig. 381. Here a pressure accumulator is unneces- 

 sary, as are valves in the high-pressure water column. For its operation 

 a low-pressure water supply, at about 200 300 Ibs. per square inch, is 

 necessary, and during the idle part of the stroke this follows up the ram, 

 the high-pressure connecting pipe being kept full in the meantime. 



FIG. 381. Allen's Hydraulic Forging Press. 



When pressure is required this supply is cut off and communication is 

 made with the high-pressure pump P. This has no valves, so that the 

 ram has a continuous up-and-down motion, the water column simply 

 following the motion of the pump plunger. The inertia of this column 

 thus has a useful effect in increasing the pressure on the ram at the end 

 of the working stroke. A steam cylinder C is usually provided for lifting 

 the ram. 



A type of forging press to be worked in connection with an accumulator 

 and intensifier is illustrated in Fig. 382. This press is fitted with a 

 differential ram having diameters of 21 inches and 36 inches and supplied 



