GB535625A - Improvements in or relating to hydraulic machinery - Google Patents

Abstract

535,625. Reciprocating pumps for liquid. ERNST, W. Nov. 3, 1939, No. 29365. [Class 102 (i)] [Also in Group XXIX] A reversible variable delivery pump has its flow control member operated by a fluid-pressure servomotor and is provided with a centring device adapted to return the control member to its neutral position in the event of the pressure supply to the servomotor failing. As shown in Fig. 3, a press 13 with a differential ram 12 is operated by a reversible variable delivery pump 1 connected by pipe lines 23, 24 to the ram cylinder 19. The pipe line 24 is connected by a pipe 27 with a surge tank 3 through a non-return valve 10 and through a relief valve 9 with a main cylinder release and byepass valve 4 which is also connected to the chamber above the ram by a pipe 28 fitted with a relief valve 8. This chamber is fitted with a surge valve 5 to admit fluid to the ram during the time the press is moving up to the work said valve having an operative connection with the pipe 27 so that it is forcibly opened during the return stroke of the ram. The deliveryvarying ring 43 of the pump 1 is operated by a differential piston 48 and is loaded towards its neutral position by a pair of springs 95, 96 engaging collars 92, 93 arranged on either side of a partition 94 and co-operating with a collar 90 on a rod 89 secured to the ring 43. The piston 48 is fitted with a liner 55 having ports 57 communicating through ports 60 with an annular chamber 51 connected by a pipe 36 with an auxiliary motive fluid pump 6 and having ports 58 leading to an annular chamber 61 connected by longitudinal passages 62 in the piston with the power chamber 49. A control valve 68 loaded by a spring 65 housed in the hollow piston rod is operable either to connect the power chamber to pressure through ports 57, 60 and pipe 36 or to a return line 38 to the surge tank through ports 58, 64 and annular chamber 52. The control valve is coupled by a lever 101 and links 99, 104 with one arm 106 of a three-armed lever 108. One arm of this lever is adapted to be operated by a tappet 16 on a rod 17 secured to the press head while the third arm is linked to the core of a solenoid 113 controlled by a switch 130 actuated by a spring- loaded plunger 117 subject to the pressure in the ram cylinder and by a starter switch for the delivery motor. When the solenoid is energized the control valve is moved in the direction required to cause the pump to deliver fluid to the top of the ram, and when the pressure on the ram cylinder reaches the desired value the switch 130 is opened to break the solenoid current which causes the control valve to reverse the pump and so retract the ram. As the ram reaches its retracted position the tappet 16 moves the control valve to the position necessary to move the pump contral 9 to its neutral position. In the event of the pump failing, the springs 95, 96 move the pump control to its neutral position.