GB957851A - Improvements in or relating to hydraulic gears - Google Patents

Abstract

957,851. Hydraulic apparatus. ISTAG A.G. April 30, 1962 [April 28, 1961], No. 16419/62. Heading F1P. An hydraulic system comprises a reversible delivery pump 1 communicating over a closed circuit having two liquid conduits 44, 58 and 45, 59 with an hydraulic motor 2, a slide valve 3 having a sliding plunger 32 which communicates at each end with a separate one of the conduits so as to be responsive to a difference in pressure existing in the conduits and effect a connection between the conduit at lower pressure and a conduit 57 between the valve housing 33 and a reservoir 15, and a check valve 34, 35 opening towards the motor provided in each of the two liquid conduits, the sliding plunger acting as an opening member for the check valve in the conduit at lower pressure. The plunger has its ends in chambers 42, 43 connected by the portions 44, 45 to the pump 1, the check valves, which consist of balls 34, 35, normally closing the portions 44, 45 from the other portions 58, 59 of the conduits leading to the differential-area piston motor 2. A reduced central portion 51 of the plunger is associated with the conduit 57 leading to the reservoir 15 and lands 17, 18 on the plunger provided with edges 55, 56 control communication between the chambers 42, 43 and the conduit 57; ribs 54 support the plunger during its movement. Extensions 47, 48 on the ends of the plunger act as opening members for the check valves. When the pump is rotating in the direction A, fluid pressure in chamber 43 moves the plunger to the left, the movement first connecting chamber 42 to the conduit 57 so that the portion 44 of the conduit which supplies fluid to the pump is connected to the conduit 57 leading to the reservoir. Further movement of the plunger causes the extension 47 to open the check valve 34 to permit fluid from chamber 26 of the motor to pass to conduit 44. The fluid pressure in chamber 43 opens the check valve 35 to permit fluid pressure to move the piston 24 to the left, excess fluid, because of the differential areas of the piston, exhausted from chamber 26 passing through conduit 57 to the reservoir. When the pump is rotated in the opposite direction, the plunger moves to the right and the fluid, additional to that exhausted from the chamber 27, pumped to chamber 26 is drawn through conduits 45, 57 from the reservoir. The arrangement compensates for any losses caused by leakage from the system. When the pump is stationary; the plunger takes up a central position and both check valves 34, 35 close to lock the piston 24 in position. In the event of a heavy load on the piston when it is in its locked position causing excessive pressure in the chambers 26, 27, adjustable pressure relief valves 70, 71 are provided connected by conduits 60, 61 to the reservoir.