U.S. Patent Specifications

In an aircraft control system, a balanced four‐way valve comprising a casing, a piston valve arranged to reciprocate within said valve casing, a source of hydraulic fluid under pressure, a conduit from said source to a centrally located port in said valve casing, a servo‐cylinder having a movable piston adapted for the operation of a movable aircraft element, fluid conduits connecting the ends of said servo‐cylinder with feed ports in said valve casing normally covered by said piston valve in its neutral position, fluid spaces within said valve casing between each end and the end faces of said piston valve adapted to contain an initial supply of hydraulic fluid, fluid conduits interconnecting said spaces with the adjacent conduits to the said ports closed by said piston valve, and means for applying manual control forces to said piston for the hydraulic operation of said movable element, such control forces acting to force an initial supply of hydraulic fluid into the servo‐cylinder prior to the uncovering of said feed ports.