GB1288129A - - Google Patents

Abstract

1288129 Fluid-pressure servomotor systems KOEHRING CO Inc 15 June 1970 [23 Dec 1969] 28896/70 Heading G3P In a control system for a fluid motor 15 compris- ing a control valve 10 having a passage 18 connected to a fluid-pressure source P and a passage 14 through which motor exhaust can be returned to a reservoir, an exhaust valve 27 blocks exhaust flow from the passage 14 until either a first pilot valve 41 is lifted by the pressure of the exhaust fluid or a second pilot valve 43 is lifted by the supply pressure. The valve 41 may be adjusted to open at 300 p. s.i. and the valve 43 at 1000 p.s.i. A check-valve 57 allows fluid to flow from the exhaust line 14, 8<SP>1</SP>, 25 to the supply line 7<SP>1</SP>, 18 and whichever of the service parts 12<SP>1</SP>, 13<SP>1</SP> is connected to the supply so as to avoid cavitation when the motor is driven by its load. This arrangement operates when the valve 10, which is of the open-centre type, is in neutral position or to supplement a conventional anti-cavitation system in which relief and check-valve 53, 54 inter-connect the ends of the motor cylinder through the passage 14. When exhaust pressure is above the pre-set value, it acts on the pilot valve 41 through an orifice 32 in the valve 27 to allow the latter to open an outlet passage 26. The second pilot valve 43 opens the valve 27 to remove obstruction to exhaust flow when the motor is heavily loaded and the supply pressure rises above the pre-set value.