Abstract: The invention relates to a valve assembly adapted in conjunction with a valve actuator to provide positive control of the stroke of hydraulic cylinders. The valve is attached to a pressure port on the cylinder and the actuator assembly is positioned on the side of the cylinder and held by means of clamps. The stroke of the cylinder is limited when the actuator arm is clamped on the piston shaft at a distance shorter than the full stroke of the cylinder. In this condition as the shaft moves into the cylinder, the actuator arm contacts closure means within the valve thereby closing off the valve and preventing further retraction of the cylinder. The apparatus of the invention is adapted to be supplied in the kit form and can be readily attached, externally to any existing hydraulic actuator.