Control Systems for Hydraulic Power Lift Mechanisms of Agricultural Tractors

摘要

A hydraulic power lift system for agricultural tractors comprises a single-acting hydraulic ram for raising the linkage to which a ground-working implement or equivalent load is attached. The system includes a spool type control valve for maintaining the implement in a desired position and a lock valve which prevents leakage of fluid from the ram and so improves positional stability. In the absence of inlet pressure to the spool valve, a safety interlock valve interrupts the supply of fluid needed to open the lock valve. Preferably the supply to the lock valve is cut-off if the control calls for position other than "raise" or "neutral" when power is resumed after a disruption.