FLUID CONTROL DEVICES

摘要

A fluid control device of the sliding spool type having pilot control wherein a control profile (20) is located in a longitudinal bore through the spool (4) and has radial clearance (22) in said bore. The control profile (20) separates respective control chambers (12, 14) which extend to the main bore in which the spool is located and an orifice arrangement (5) in the wall of said spool (20) directs secondary fluid flow from a pressure port (10) onto said control profile and into said chambers (12, 14) whereby an imbalance in the chamber pressures will cause sliding movement of the spool. Further respective orifices (6, 8) allow said secondary flow to return to the low pressure side of a fluid supply. The control profile (20) is arranged on a rod which extends externally of the body of the device and sliding movement of the rod causes imbalance of a hydraulic Wheatstone bridge formed by the orifices (5, 6, 8) in combination with the control profile (20) whereby the bridge tends towards equilibrium causing the spool (4) to follow movement of said control profile (20) in a force feedback gain manner. The device has a position feedback ratio of 1:1.