A valve body has an outside surface and a cylinder. The cylinder has an inlet chamber and an outlet chamber. A piston has a head at one end and a foot at the end opposite the head and a piston body between the head and the foot. A cross channel extends from a first side of the piston body. A longitudinal channel is in fluid communication with the cross channel and extends to the outlet chamber. The piston is positioned in the cylinder so that it can be moved to an open position in which the cross channel is in fluid communication with the inlet chamber and a closed position in which the cross channel is not in fluid communication with the inlet chamber. The piston is actuated between the two positions by a differential in pressure between the inlet chamber and the outlet chamber.