Abstract: A sub-surface hydraulically operated engine for reciprocating an oilwell pumping unit includes confined hydraulic fluid means for actuating a reversing valve and its lifter in order to change the upstroke motion to downstroke motion and vice-versa.

Abstract: A downhole oil well hydraulic pump has a reciprocating piston assembly with a piston ring mounted in a groove around the piston. This piston ring groove has a main portion which loosely mounts a piston ring and an auxiliary portion joining the main portion which accumulates well fluid to lubricate the piston ring during operation of the pump.

Abstract: A reversing control valve for a fluid operated downhole oil well pump having reciprocating pistons that is constructed to control the velocity and reversing of the pistons. The control valve functions to control the piston velocity and prevent damage to the pump components due to shock stresses induced by pressure impulses typically associated with pumped well fluids. The reversing control valve is constructed to regulate the piston velocity in response to the sensing of several pressure conditions in the well and in the pump.

Abstract: A seal assembly for a downhole hydraulically operated oil well pump has a dovetail shaped groove around the exterior of the pump body and a seal element mounted therein. The seal element has an inner side resting against the groove bottom, one end of a full thickness filling that end of the groove and extending therefrom toward the opposite end having a recess portion around the outer perimeter thereof forming a lip about a mid-portion of the seal element which is deformed by fluid pressure acting toward that end of the seal to urge the lip outward into sealing contact with a pump housing which encloses the pump body.