Hydraulic control valve unit

摘要

A self-monitoring hydraulic control valve unit has a main valve and a control valve for controlling supply of hydraulic fluid to a control duct of the main valve. A differential piston is connected in the control duct and has a longitudinal bore which forms part of the control duct, the piston acting at its smaller diameter end on the shutter of the main valve. An electrical monitoring switch such as a proximity switch monitors the position of the differential piston and, therefore, of the main valve.