Improved Hydraulic Control System for Lift Ram

摘要

1,177,900. Masted lift truck. ALLISCHALMERS MFG. CO. 23 Dec., 1968 [2 Jan., 1968], No. 61090/68. Heading B8H. [Also in Division F1] An hydraulic circuit for the control of the lift ram includes a primary pump and a secondary pump to provide a high-speed lift operation, the circuit being such as to necessitate only a single relief valve. As shown, on moving the control valve 24 to the " lift" position, a contactor 63 bridges contacts 61, 62 to energize the motor 22 of the pump 21 which supplies fluid through a line 23 and a check valve 34 to the lift ram 11. Further movement of the control valve 24 causes a contactor 66 to bridge contacts 67, 68 to energize the motor 38 of the secondary pump 37 which supplies fluid, through a line 36 and a check valve 39, directly to the ram. A pressure relief circuit for the primary pump comprises a by-pass line 41 and a relief valve 42, which is connected to the secondary circuit by a line 46 and a check valve 47. The primary circuit includes a control valve 31 for controlling a mast-tilting ram 19.