GB918259A - Improvements in or relating to fluid supply means for hydraulic presses and the like - Google Patents

Abstract

918,259. Hydraulic presses. LANGDALE ENGINEERING CO. Ltd. Jan. 17, 1962 [Oct. 20, 1960], No. 35917/60. Class 69 (2). A fluid supply system for an hydraulic press or the like required to make a long rapid approach movement at low pressure followed by a short slow movement at high pressure comprises a displacement unit A consisting of a small bore cylinder 1 in tandem with a larger bore cylinder 3, a connection 9 in the cylinder 1 to apply high pressure from a source 8 to one end of a small piston 2 which extends into the larger cylinder to effect movement of a large piston 4 against a spring 5, a non-return inlet 6, 7 in the end of the larger cylinder remote from the small cylinder for admitting operating fluid when the piston 4 is free to be moved by the spring, a sequence valve B having an inlet 10 for connection to the same high pressure source 8 and an outlet 11 leading to the cylinder 21 of the press, and an outlet 13 and non-return valve D connecting the larger cylinder to the outlet 11 from the sequence valve to the press cylinder. The sequence valve B has a spool 23 urged by a spring 26 to a position closing the outlet 11 so that the pressure from the source 8 acts initially only on the small piston 2 which moves the larger piston 4 against the spring 5 to displace fluid through the outlet 13, non-return valve D, a control valve C and lines 19, 20 to the upper end of the press cylinder, the fluid from the lower end of the cylinder passing to an exhaust 28. When the ram encounters resistance, the increase in pressure in the press cylinder 21 acts through a passage 25 on to the end of the spool 23 of the sequence valve B which is moved against the spring 26 to connect the source 8 directly to the press cylinder, the non-return valve D preventing the high pressure fluid entering the cylinder 3. At the completion of the pressing operation, the control valve C can be operated to reverse the connections to the press cylinder so as to raise the ram, but the actual movement of the valve is restricted by the high pressure in the upper end of the press cylinder acting through a line 29 on the control valve so that the exhaust 28 is only partially open, the fluid from the upper end of the cylinder passing through the partially-open exhaust until such time as the pressure drops sufficiently to permit the full movement of the valve to be effected. At the same time a by-pass 26, which normally unloads the source 8 when the control valve is in its neutral position, is opened to relieve the piston 2 and enable the spring 5 to return the piston 4 and fluid from a tank mounted on the upper surface 16 of the displacement unit to pass through a port 6 and non-return valve 7 to recharge the cylinder 3. A relief valve E may be provided which together with the sequence valve B and non- return valve D may be mounted in the displacement unit, the ports being interconnected by hollow bars secured to the units.