GB1157291A - Improvements in Hydraulic Systems - Google Patents

Abstract

1,157,291. Press-brakes; shearing. SPERRY RAND Ltd. 27 Sept., 1966 [21 Oct., 1965], No. 44604/65. Headings B3E and B3W. [Also in Divisions B5 and F1] A system for causing double-acting hydraulic jacks 1, 2 to move in unison in either direction for operating, e.g., the blade of a shearing and bending machine, comprises coupled reversing valves 3, 4 for the jacks and a control valve 9 controlled in response to the difference in displacement of the jacks to vary the flow to the jacks so as to reduce the difference in displacement, each valve 3 or 4 controlling in one position the advance of one jack and in its other position the withdrawal of the other jack. When the valves 3, 4 are first changed over by simultaneous energization of associated solenoid valves, and assuming the jacks are only lightly loaded, a large flow low pressure pump 7 supplies the jacks through a flow-divider 12 and the control valve 9 proportions the flow to the jacks from a low flow high pressure pump 6. If the load on the jacks increases, pressure builds up in a pilot line 11 to cause a valve 10 to open and by-pass the output from the low pressure pump 7. The jacks are then operated solely by the pump 6, non-return valves 13, 14 preventing return flow through the flow-divider 12. Two arrangements for detecting the difference in displacement of the jacks and controlling the valve 9 are described. In the first, Fig. 2 (not shown), each jack piston causes rotation, through rack-and-pinion gearing, of a shaft. The shafts are connected through a screw-andnut connection, whereby differences in their rotation cause axial movement of the nut and consequential adjustment of the valve 9. The second arrangement, Fig. 4 (not shown), comprises two drums each driven by a cable connected to the jack piston, the movements of the drums being transmitted to a differential rotary servo valve providing an hydraulic output for adjusting the valve 9.