Electrohydraulic pilot controlled four way directional hydraulic valve - ensures closed centre operation by spring action combined with spool ends that locate with stop shoulders contacting bushes

摘要

A pilot controlled 4 way hydraulic valve has a main stage (14) in which a spool (30) is held in the closed centre position in the absence of control signals from the pilot valve (12). The ends of the spool (44,46) locate in guide bushes (52, 54). The spool has formed shoulders (48, 50) in contact with the bush and, under the action of spring forces (60, 62), these shoulders define the centre position. The control signals applied to the end of the spool are provided by the outputs (35, 37) of the pilot valve. The spool of the pilot is displaced by solenoid actuators (22, 24). ADVANTAGE - Improved response and reliable fail-safe centre positioning of main spool.