GB564190A - Improvements in or relating to control valves for hydraulic systems for hydraulic presses - Google Patents

Abstract

564,190. Hydraulic presses. ERNST, W. Nov. 12, 1942, No. 15996. Convention date, Jan. 10. [Class 69 (ii)] In a hydraulic press having a piston 75 both advanced and retracted by fluid pressure from, for example, a reversible motor 96, a valve 9 is adapted, as the piston 75 reaches the end of its stroke and pressure builds up behind it, to establish a byepass which when the -pump reverses byepasses the retractive fluid admitted below the piston, the byepass then being automatically and gradually decreased at a rate determined by an adjustable choke and that is independent of the rate of decrease in pressure above the piston. The increased pressure at the end of the forward stroke also serves, in the arrangement shown, to operate a switch 86 which breaks the circuit of a solenoid 87 so that a rod 92 moves to the left and a servomotor 95 reverses the pump 96 ; at the end of the return of the piston 75 a collar 101 on the piston returns the rod 92 to a neutral position. The valve 9, Fig. 2, comprises a main plunger 15 movable against a return spring 21 by fluid pressure introduced at 28 and serving then to connect an inlet port 26 with an exhaust port 31 and the operating port 28 with a channel 62 leading to an auxiliary bore which contains a plunger 14 movable to the left against a spring 54 by fluid pressure introduced at 67 through a channel connecting 67 with a passage 64 permanently connected with the inlet port 26. The ports 26, 28 are connected to the hydraulic system as shown in Fig. 1. When, in the forward stroke of the piston 75, resistance is offered by a workpiece and pressure builds up above the piston, this pressure, acting through line 80, port 26, passages 64, 67 moves the auxiliary plunger 14 to the left. When the pump 96 reverses, the pressure from it acting along lines 108 and 28 moves the main plunger 65 to the left so that, instead of acting to push up the piston 75, some of it is byepassed through 28, 62 to an exhaust 60 now connected to 62 owing to the movement of the auxiliary plunger. This byepass is then gradually throttled at 48 as the auxiliary plunger 14 moves to the right owing to the decreased pressure in the passages 67, 64 which are now, as well as the port 26, connected to the exhaust 31. An adjustable choke between 67 and 64 regulates the speed of movement of plunger 14 and hence the rate at which pressure below the piston 75 increases. Specifications 519,824, [Group XXXVII], and 535,625 are referred to.