Abstract: Spool valve for fluid systems, the valve having a slidable spool in a bore in a valve block having three ports spaced aially along the bore for control of fluid flow, the spool having three spaced O-ring seals to correspond with the ports and having a reduced diameter portion between two of the O-ring seals, and a pressure-equalizing conduit connecting one end of the spool with the outlet port of the valve. Small lands of substantially equal diameter to the spool adjacent the reduced diameter portion before the two O-ring seals provides restricted or throttled fluid flow prior to increased fluid flow via reduced diameter portion.

Abstract: The actuator includes a power-assisted main mechanical linkage connecting the clutch pedal lever to the clutch plate lever. The power-assisting assembly is supplied high pressure air and is actuatable by pedal-driven movement of the main linkage. A manually operable piston and cylinder device operates to vary the movement of the linkage and therefore alter the action of the applied force to the main linkage for a reduced pedal stroke mode of operation. The actuator is operable in one of two modes: a power-assisted mechanical mode wherein mechanical force applied to the linkage is dominant; and a selectable power-assisted/mechanical mode with a reduced pedal stroke length wherein the power-assist is the dominant operating force. In either mode, the main mechanical linkage is always operatively connected between the pedal lever and plate lever to provide for purely mechanical operation in the event of air pressure failure.