Electrohydraulic control valve - has fail-safe position provided by fluid pressure acting on sliding control piston

摘要

The valve has a housing (3) with a pressure feed channel (29) and at least 2 working channels (31,33), containing a control piston (7) displaced relative to a longitudinal channel (49), sealed at one end by a valve device (17). The control piston (7) is displaced against a spring bias via a proportional magnet (25) between a neutral position and 2 working positions, with a fluid pressure used to displace the piston (7) into a fail-safe position. The pressure supply to the working channels (31,33) and/or the latter are coupled together in the fail-safe position. The bias spring (15) cooperates with stops (19,9) which only allow it to act on the control piston (7) when the latter is in the neutral position or one of the 2 working positions. ADVANTAGE - Optimum fail-safe control i.e. reacts rapidly but not too soon. Danger risks for operator(s) removed.