Abstract: A pump is disclosed comprising a piston plunger with a valve disposed in it. The ratio of the flow area on either side of the valve is optimized.

Abstract: A fluid pump is disclosed having a plunger reciprocating within a working cylinder and a standing intake retention valve. The plunger comprises a stem having affixed to it a plug and a stop, a body being slidably engaged to the cylinder an located on the discharge side of the plug and on the intake side of the stop. Upon the upstroke of the plunger, a plug surface engages with a body seal and therefore pumps the fluid before it. Meanwhile, fluid flows in behind the plunger through the standing intake retention valve. Optionally, a standing discharge retention valve is employed to alleviate the vapor lock condition caused by the combination of counterpressure effect and gases in the fluid. On the downstroke, the plug disengages from the body, allowing fluid to flow noncompressibly past the plunger. Wiper means keep the cylinder surface clean of precipitated solids, so as to prevent abrasion to the sliding exterior surface of the body.