Hydraulic control valve having a centering spring device

摘要

Centering spring devices are useful in hydraulic control valves for returning the valve to the neutral position under both normal and abnormal operating conditions. Since the actuator moving the valve spool must work against the spring centering device, electrically actuated hydraulic valves have been limited to small sizes. The subject hydraulic control valve incorporates a centering spring device that can be controllably disabled so that the valve spool can be freely moved between the neutral and operating positions. In one embodiment, a centering spring is disabled by hydraulically moving the spring retainers toward each other to compress the spring with hydraulic fluid controlled by a solenoid valve. Maintaining the spring in a compressed condition permits the valve spool to be moved with a smaller actuator thereby making it feasible to control the valve position with an electrical actuator.