Pressure unloading apparatus for a diaphragm pump

Claim 1

A diaphragm pump apparatus of the type having a mechanically reciprocated piston driving a pumping diaphragm through an intermediary hydraulic fluid displacement chamber to cause the pumping diaphragm to deflect to pump liquid through an inlet and outlet check valve to an output, comprising: a. a hydraulic fluid reservoir in said apparatus for storing a supply of hydraulic fluid; b. a fluid chamber having a passage to said hydraulic fluid reservoir and having a connecting port to said displacement chamber; c. a valve in said passage between said fluid chamber and said hydraulic fluid reservoir, having a valve surface exposed to said displacement chamber pressure to develop valve opening forcing thereon d. a passage between said fluid chamber and said output and a control diaphragm interposed across said passage in fluid sealing relationship; e. a slidable plunger adjacent, but not connected to, said control diaphragm, and spring biasing means for urging said plunger toward said control diaphragm; f. a rod connected between said plunger and said valve for translating control diaphragm deflection to valve opening and closing motion; g. a valve passage between said displacement chamber and said reservoir, said valve passage having therein a check valve openable by an excess differential pressure in said reservoir relative to displacement chamber; and h. a slide valve connected to said pumping diaphragm and slidable over said valve passage to open said valve passage during a maximum deflection of said pumping diaphragm