Abstract: An improved pilot valve construction for use in a fluid and mechanically actuated double diaphragm pump which includes a housing, first and second axially spaced fluid pressure chambers, first and second flexible diaphragms disposed in the pressure chambers and mechanically interconnected for simultaneous reciprocal movement and each defining a flexible wall of an adjacent pumping chamber and a pilot valve projecting axially into the pressure chambers and slidable axially in response to engagement by one of the diaphragms and wherein the pilot valve is provided with one or more axially extending grooves in its peripheral surface. The pilot valve may also be provided with a radially extending projection in its peripheral surface.