Abstract: A power assist remotely controlled servo controller for proportionally controlling the operation of a directional control valve, the controller including a servo-controlled force amplifying piston assembly to operate the directional control valve and a pilot pressure balanced piston connected to the servo-controlled piston assembly to control the directional control valve. The balanced pilot pressure forces acting on the pressure balanced piston being controlled by either a hydraulic or electric controller from a remote location.

Abstract: A pressure compensating valve spool assembly for a hydraulic flow control valve the spool assembly being slidably positioned in the central bore of a valve housing for movement from a neutral position wherein fluid will flow through the valve assembly to reservoir to operative positions in either direction to provide fluid communication between fluid inlet passages to one of a pair of cylinder passages in the valve housing, the other of said cylinder passages being connected to one of the pair of reservoir passages. The valve spool assembly includes a symmetrical valve spool having valve members at each end which are responsive to variations in the pressure relation between inlet pressure and cylinder pressure to control the fluid flow rate to the cylinder passage. Any excess flow is bypassed to reservoir at minimum pressure loss.