Improvements in a Hydraulic Control System for moving equipment, such as Excavators and Cranes

摘要

A hydraulic control system comprising a hydraulic actuator (20) having opposed openings adapted to alternately function as inlets and outlets for moving the element (21) of the actuator in opposite directions, a pump for supplying fluid to the actuator, and a meter-in valve (27) to which the fluid from the pump is supplied. The meter-in valve (27) is pilot controlled by alternately supplying fluid at pilot pressure to the meter-in valve (27) for controlling the direction of movement of the actuator. A pair of lines (32, 33) extend from the meter-in valve (27) to the respective openings of the actuator. Valves (34, 35) are positioned between a tank passage and each opening of the actuator for controlling the flow of fluid between the actuator and the tank passage; and at least one of these valves (34, 35) is normally open and pilot operated.