A control valve includes a piston-housing having a hollow portion. The hollow portion has a first end, an open end, first and second internal chambers, and a fluid port configured to allow fluid to exit the second chamber. The first chamber is nearer the first end, and the second chamber is nearer the open end. A piston is located within the housing and is adapted for reciprocal motion. The piston includes a first and second seal-engaging portions. The first seal-engaging portion has a diameter that is less than the diameter of the second seal-engaging portion.