Designed to lock a cylinder or part of a circuit while a directional control valve is in the neutral position. With directional control valve in neutral position, flow from both ends of cylinder is blocked locking cylinder piston in position. When directional control valve is shifted to direct flow to one side of the cylinder, pressure opens the check ball and simultaneously moves the piston over to the opposite side of the valve opening this check valve allowing free flow return to the directional control valve. Max:15 GPM, 3000 PSI.