GB611632A - Improvements relating to hydraulic press plant - Google Patents

Abstract

611,632. Hydraulic presses. PRECISION DEVELOPMENTS CO., Ltd., OLAH, G., and BOX, F. J. March 23, 1946, No. 9033. [Class 69 (ii) In an apparatus comprising a main pump 1 and an auxiliary pump 2 supplying liquid through an unloading valve 3, feed pipe 4, and a control valve 7 to an hydraulic press, the control valve is actuated by a rod 11 which is loaded by a spring 13 or other equivalent means to urge the valve to its return-stroke position but during the operating stroke of the press the valve is prevented from moving by a trigger bar 14 engaging a notch 15 in the rod. The trigger bar is attached to a differential piston 17 in a cylinder 16 communicating through a pipe 19 with the main pump 1 and through a non-return valve 22 to the feed pipe 4. This non return valve is byepassed by an adjustable hydraulic resistance element 23. During an operating stroke of the press the trigger bar 14 is kept in engagement with the notch 15 by the liquid pressure from the main pump acting under the piston 17. When at the end of the stroke pressure increases to move valve 3 so that the main pump unloads, pressure under the piston 17 disappears and liquid from the pipe 4 flowing through the element 23 forces the piston downwards until after a predetermined time the rod 11 is free to be moved by the spring 13 to put the valve 7 in the position to cause the return stroke of the press. The unloading value 3 may be constructed as described in Specification 611,628.