GB1320544A - Fluid control system - Google Patents

Abstract

1320544 Controlling pumps AUTOMATIC DRILLING MACHINES INC 1 July 1970 31880/70 Heading F1A [Also in Division G3] The flow of fluid to and from a power operator, such as cylinders 22 for effecting vertical movement of a drillhead 24, is controlled by a variable displacement pump 32 having a relief valve 66 and a check valve 68 connected between its inlet and outlet to maintain a downstream pressure in excess of the upstream pressure when the drillhead is being lowered. Operation of the pump as a motor is thus prevented and the descent of the load is controlled by the setting of a potentiometer 62 which determines the pump displacement through a torque motor 58, a servovalve 56 and cylinders 40, 32 coupled through a yoke to the cylinder block of the pump. A feedback signal from a potentiometer 63 controlled by the yoke is compared with the signal from the potentiometer 62 by a differential amplifier 60. The control system for the pump is charged through a check valve 76 and is pressurized by a constant displacement pump 50 connected to the system through a filter 52 and a relief valve 54. A second constant displacement pump 42 supplies the pump 32 with cooling oil which is returned through a check valve 48 to a sump 44 from which both pumps 42 and 50 draw their supply through a filter 46. The maximum output pressure of the pump 32 is controlled by a relief valve 72 while a check valve 70 prevents the pump 32 from running dry after all the fluid has been removed from the cylinders 20 and 22. A heat exchanger 75 cools the fluid discharged by the relief valve 66 which may be pilot controlled.