Patent ID: 7090474

Claim:
A diaphragm pump for receiving drive power from a motor, comprising: a housing having a pumping chamber adapted to contain fluid to be pumped, a transfer chamber adapted to contain hydraulic fluid, and a hydraulic fluid reservoir; a diaphragm having a transfer chamber side and a pumping chamber side, said diaphragm being supported by said housing and forming with said housing said pumping chamber on said pumping chamber side and said transfer chamber on said transfer chamber side; a piston in a cylinder in said housing adapted for reciprocating said diaphragm to have a power stroke and a suction stroke, said cylinder forming a portion of said transfer chamber, said piston including a first fluid communication path for the hydraulic fluid between said hydraulic fluid reservoir and said transfer chamber and a valve spool and a first valve in said first fluid communication path for selectively allowing flow of hydraulic fluid from said hydraulic fluid reservoir to said transfer chamber when said first valve is open; and an overfill preventive arrangement for said transfer chamber; wherein said overfill preventive arrangement includes a mechanical stop on said piston along a path of motion of said valve spool and a biasing element engaging said valve spool, wherein said biasing element has a spring constant counterbalancing a suction force and said mechanical stop directly engages said spool valve to stop movement of said valve spool during the suction stroke to position said valve spool to close said first valve and prevent overfilling of the transfer chamber to protect said diaphragm from being deformed beyond a design limit due to said transfer chamber being filled beyond a maximum fill condition to an overfill condition.