Patent GB-574475-A (GB)
Title: Hydraulic system
IPC: B30B15/16
Filed: 1944-02-02
Abstract: 574,475. Hydraulic systems. BECKER, W. Feb. 2, 1944, No. 1913. Convention date, Dec. 26, 1942. [Class 69(ii)] In a hydraulic system in which a press or like motor is supplied by a pump driven by an electric motor or other prime mover, fluid operable servomotor or other control mechanism is provided to prevent the pump delivering fluid to the motor whilst the prime mover .and the pump are being put into operation, i.e. until they reach a predetermined speed. In the form shown, if the press ram 2 has stopped in an intermediate position, it is retracted by closing the line switch 69 and a starter button 87. Contactor R1 closes switches R1a, R1b, R1c and opens switch R1d, whilst timer T operates for a set time sufficient to bring the main motor 77 to a desired speed. The closing of switch R1a enables starter button 87 to be released, the closing of switch R1c energizes solenoid S1 which moves valve member 42 to the right, and the closing of switch R1b energizes contactor R2. This closes switch R2a and at the same time starts the main and auxiliary motors 77, 79. The flow control member of the reversible variable delivery pump 20 is held in the no-delivery position by springs 54, 55, whilst the pilot pump 48 idly pumps fluid through the reservoir 38. When the motor 77 reaches its desired speed, timer switch T1 opens temporarily. This opens switches R1a, R1b, R1c and closes switch R1d. The opening of switch R1a allows spring 46 to return the valve 42 to the left, so that fluid from the pump 48 moves a servomotor plunger 18 to the left and places the pump 20 on its retraction stroke. This raises the ram 2, the expelled fluid passing partly to the suction side of the pump 20 and partly through a surge valve 62 into reservoir 38. An arm 4 on platen 3 acting through linkage 14 moves the servomotor valve 17 to the right. This allows the plunger 18 to be moved to the right and brings the pump 20 to its no-delivery position, the pump 48 byepassing through a pressure relief valve 51. To start a working cycle of the ram 2, the. forward switch 72 is closed. This energizes the main solenoid 12 and its armature 11 acts through the linkage 14 to move the valve 17 to the right. This allows the plunger 18 to be moved to the right and places the pump 20 on its forward stroke to depress the ram 2, this being supplemented by fluid passing through the surge valve 62 from the reservoir 38. When the platen 3 approaches the work, a cam 95 closes a limit switch 93, solenoid S1 is energized and causes valve member 42 to move to the right. Fluid may now escape from the servomotor and the springs 54, 55 move the plunger 18 to the left and decrease delivery of the pump 20, the rate of decrease being determined by a choke 31. When the platen 3 has engaged the work, the switch 93 opens, the above sequence is reversed, the pump 20 returns to its full delivery, and the ram 2 performs its actual pressing stroke. At the end of this stroke a tonnage control valve 60 opens a switch 60a and de-energizes the main solenoid 12. The valve 17 is moved to the left by spring 52, and allows plunger 18 to be moved to the left. The pump 20 is now in its retraction stroke and the ram moves upwardly. The ram may be stopped at any position by opening stop switch 70, and, on its advancing stroke, it may be returned to its retracted position by opening reverse switch 84. If the ram has stopped in an intermediate position, it cannot be lowered by accidentally closing the forward switch 72, whether or not the starter button 87 is closed. Both pumps 20, 48 may be driven by a single motor 77, the pump 48 and motor 79 may be replaced by an accumulator, and the solenoid S1 may be deenergized manually when the motor 77 reaches its desired speed. Specification 519,824, [Group XXXVII], and U.S.A. Specification 2,193,248 are referred to.