GB607127A - A new or improved hydraulic system for unloading large capacity pumps - Google Patents

Abstract

607,127. Hydraulic presses; valves. TOWLER, J. M., and TOWLER, F. H. May 25, 1945, No. 13116. [Classes 69 (ii) and 135] [Also in Group XXVIII] In a hydraulic system for controlling the supply of liquid to a hydraulic press comprising a large capacity pump for supplying the main liquid for operating the press ram and a small capacity pump for maintaining constant pressure in the delivery main, there is provided an automatically operating control means having two valve portions, one of said portions controlling the delivery of the large capacity pump so that said delivery is diverted wholly to exhaust at a predetermined pressure in the delivery main, the other valve portion controlling the delivery of the small capacity pump whereby it is caused to maintain pressure on the press ram after the large capacity pump has been cut out, the valve portions both being subject to a common load so that the maximum pressure generated by the two pumps is controlled by a single adjustment. The system includes a large capacity pump A, Fig. 2, a small capacity pump B, Fig. 1, of the kind described in Specification 567,105, an amplifier unloading valve C, and a master control valve E. The pump B delivers liquid through a pipe 8, valve E, and pipe 11 into a space 5 in the valve C where it is joined by liquid delivered by pump A into a pipe 2, the delivery then being made through pipe 6 to the press. The valve C houses a plunger 14 and a helicallygrooved piston 13, the space above which is exhausted at a predetermined pressure through a pipe 48. At this pressure liquid delivered by the pump A raises the plunger and piston, thereby gaining access to an exhaust pipe 7. The right-hand portion of the valve E houses a valve plunger 30 operated by pressure liquid acting on the right-hand side of a piston 41, a relief valve 27, an exhaust outlet 28 and an outlet 25 for connection via pipe 12 to the unloading valve D of pump B, so that this portion of the valve E controls the delivery of pump B and allows it to maintain pressure on the press after the pump A has been cut out. The left-hand portion of valve E houses a valve plunger 46 which is moved by the plunger 30, both plungers being subject to an adjustable load imposed by a spring 40. Movement of the plunger 46 connects the pipe 48 to exhaust outlet 28 so that this portion of the valve controls the delivery of pump A to divert it wholly to exhaust at the predetermined pressure imposed by the spring 40. The amplifier unloading valve may be dispensed with, a non- return valve being introduced through which the pump A delivers into the main pressure main, said pump being unloaded directly by the left-hand portion of the valve E. Figs. 6 and 7 (not shown) illustrate a type of valve E, one portion of which controls the unloading of the large pump A, the other portion unloading directly the small capacity pump after the pump A has been unloaded, thus permitting the small pump to be of the non-sustained pressure type. The pump A may be unloaded through an amplifier unloading valve or directly through the control valve, in which case a non-return valve is fitted in the circuit. Specification 604,757 is referred to in the Provisional Specification.