Air pressure-actuated double-acting diaphragm pump with means to produce a selected start-up position

Claim 1

In combination with a two-stage pump which includes a pair of reciprocating pump members operating in opposed pump chambers and a connecting rod connecting the pump members to cause the pump members to operate in unison, a control valve for supplying air under pressure to said pump chambers which comprises a spool valve member, a guide sleeve guiding said spool valve member for reciprocation, said spool valve member including an inner pair of outwardly extending portions defining a central pressure slot and an outer pair of outwardly extending portions, each of the outer pair defining an exhaust slot with one of the inner pair, means in the sleeve for connecting the central pressure slot with a source of air under pressure, means in the sleeve for releasing pressure in each of the exhaust slots, a first port in the sleeve communicating with a first one of the chambers, a second port in the sleeve communicating with the other of the chambers, the spool valve member moving between a first limit position in which the first port is in communication with the pressure slot and the second port is in communication with one of the exhaust slots to cause movement of the connecting rod and the pump members in one direction and a second limit position in which the second port is in communication with the pressure slot and the first port is in communication with the other of the exhaust slots to cause movement of the connecting rod and the pump members in an opposite direction, there being pressure chambers at opposite ends of the sleeve member, means controlled by the connecting rod for supplying air under pressure to one of said pressure chambers when the connecting rod is in one position to cause movement of the spool valve member toward the other of said pressure chambers, means controlled by the connecting rod for supplying air under pressure to the other pressure chamber to cause movement of the spool valve member toward the first pressure chamber when the connecting rod is in a second position, and means releasably engageable with the spool valve member for advancing the spool valve member to one of the limit positions to position the spool valve member for starting the pump, there being metering air passageways exhausting air from the pressure chambers.