Patent ID: 7425120

Claim:
A diaphragm pump, comprising: a piston adapted for reciprocal movement between a first position and a second position, the reciprocal movement defining a piston stroke; a diaphragm movable between first and second positions that correlate with the first and second piston positions; a pumping chamber on one side of the diaphragm; a transfer chamber on the other side of the diaphragm defined in part by the first and second positions of the diaphragm and the piston, the transfer chamber being filled with a hydraulic fluid; first and second valves; a fluid reservoir in fluid communication with the transfer chamber via the first and second valves; a valve spool positioned in the transfer chamber and movable in the transfer chamber relative to the diaphragm, the valve spool arranged to cover openings to the first and second valves when the valve spool is in a first position, to cover the opening to the first valve and open the opening to the second valve when the valve spool is in a second position, and to open the opening to the first valve and cover the opening to the second valve when the valve spool is in a third position; wherein the spool maintains the first position independent of movement of the diaphragm until an overfill condition is generated in the transfer chamber that moves the valve spool to the second position, or until an underfill condition is generated in the transfer chamber that moves the valve spool to the third position.