Abstract: A liquid pump is disclosed having a center block containing inlets and outlets for liquid to be pumped and air to operate the pump with associated valves for liquid and air. A pair of opposed cylinders are provided on opposite sides of the center block and each containing a collapsible bellows connected to a sleeve forming a piston with the liquid being pumped in the chamber within the bellows. Push rodes extend from one piston to the other so that the piston pumping liquid out pushes the other piston to fill with liquid. The bellows have conbolutions of selectively varying wall thickness, and tapered single or dual compression seals are provided where the bellows are joined to the center block. An inflow conical valve and an outflow shuttle valve are provided for each cylinder, and vent tubes are provided to cool the bellows and to actuate the air valve at the end of the piston stroke. An encapsulated sheet member is provided in each cylinder.