A pump includes a liquid housing having a liquid chamber with a piston/diaphragm assembly arranged therein that responds to a suction stroke and draws liquid into the liquid chamber, and responds to a pressure stroke and provides liquid from the liquid chamber; and a gas housing having a slide valve assembly separating first and second gas chambers. The slide valve assembly responds to a suction-to-pressure-force at the suction stroke conclusion, changes from a suction-to-pressure stroke state, provides gas from the first to second gas chamber through the slide valve assembly, and provides the pressure stroke so liquid passes from the liquid chamber; and responds to a pressure-to-suction-force at the pressure stroke conclusion, changes from the pressure-to-suction stroke state, provides gas from the second chamber through the slide valve assembly, and provides the suction stroke so liquid is drawn into the liquid chamber.