A pilot control relay valve having first and second elongated valve members coaxially and independently longitudinally shiftable within a valve body between a first position of the first or leading valve member thereby allowing communication of actuating fluid from a supply to a first pressure receiving surface of the second or following valve member to initiate movment of the second valve member from its first position to a second position thereby allowing communication of the actuating fluid to a first pressure receiving surface of a main piston to initiate movement of the first valve member to a second position of the first valve member thereby allowing communication of supply fluid to the second pressure receiving surface of the second valve member thereby initiating movement of the second valve member from its second to its first position thereby allowing communication of supply fluid to a second pressure receiving surface of the main piston to initiate movement of the first valve member to its first position whereby the operation is repeated ad infinitum.
