Piston pumps driven by fluid-actuated piston having a constant fluid force against the small area surface

A reciprocating pump for liquids comprising a body, a piston slideably disposed within said body and having a large area face and a small area face, a shuttle valve casing associated with said pump body and having a motive air inlet and a motive air exhaust, a valve shuttle operable with respect to said motive air inlet and motive air exhaust having a large area face and a small area face disposed in said casing between said motive air inlet and motive air exhaust, and the large area face of said piston, said valve shuttle being slideable in said casing between a first position wherein it occludes said motive air inlet and a second position wherein said motive air inlet communicates with the large area face of said piston, signal air inlet means provided in said pump body and opening on the small area face of said piston, said signal air inlet means being positioned to continuously maintain signal air pressure on said small area face for all portions of said piston and at the same pressure as said motive air, first conduit means provided in said pump body and shuttle valve casing between said signal air inlet and the large area face of said shuttle valve for signal air flow to drive said valve shuttle into said first position, second conduit means provided in said pump body and shuttle valve casing between said signal air inlet and the small area face of said valve shuttle for signal air flow to drive said valve shuttle into said second position whereby said piston is driven in a pumping stroke by the pressure of said motive air against the large area face of said piston, hydraulic fluid receiving chamber means provided within said pump body and defining an inlet and outlet, and a pump ram for relative reciprocal movement within said chamber means responsive to movement of said piston, said pump ram expelling hydraulic fluid from said chamber means during a pumping stroke of said piston.