Abstract: A relay valve for use with a railroad car braking system includes a housing in which a control chamber is disposed between a delivery chamber on an upper side and an exhaust chamber on a lower side. A supply chamber is disposed above the delivery chamber. A control piston disposed in the control chamber is reciprocally-movable as a function of the balance of forces acting on opposing sides of the piston. In order to achieve the desired balance of control fluid pressure to delivery fluid pressure, the surface areas of the piston on which these pressures are exerted are equalized by way of a hollow rod extension coaxially-disposed on the piston, and extending from the lower exhaust chamber to the upper delivery chamber.