Mechanical shift, pneumatic assist pilot valve for diaphragm pump

A combination mechanical and fluid operated pilot valve construction for a double diaphragm pump comprising, in combination:

• a housing defining an axis with first and second axially spaced fluid pressure chambers in a double diaphragm pump;
• first and second diaphragms arranged in the first and second pressure chambers, respectively, to define a flexible wall in each of said pressure chambers, said diaphragms generally transverse to the axis, said diaphragms mechanically connected for generally simultaneous, reciprocal movement in the axial direction, said diaphragms each also defining a flexible wall of an adjacent pumping chamber;
• and
• a pilot valve assembly having a single fluid inlet, a first outlet to the first chamber and a second outlet to the second chamber, said pilot valve assembly also including a fluid operated slide valve reciprocal to connect the inlet to the first or second outlets;
• said fluid operated slide valve including a differential surface area fluid actuator having a minor and a major surface area;
• said assembly also including a mechanically shiftable pilot member projecting axially into the pressure chambers and slidable axially in response to engagement by one of the diaphragms said slide valve and actuator comprising an elongate spool valve translatable axially in the housing, said spool valve including a slide member along one side, said slide member cooperative with the first or second outlets and an intermediate exhaust passage whereby only one or the other outlet is connected to the exhaust passage as the other or one outlet is connected to a pressurized fluid inlet;
• first and second fluid pressure passage to the fluid actuator minor and major surface areas, respectively, said first pressure passage communicating directly with the minor surface area, and the second pressure passage communicating through the mechanically shiftable pilot member to the major surface area;
• and
• said mechanically shiftable pilot member including a fluid connection passage which interconnects, the first and second pressure passages to provide pressurized fluid flow into the second pressure passage upon mechanical shifting of the pilot member the other diaphragm.