Abstract: A hydraulic intensifier for oil well fracturing and/or erosion drilling, having a pair of intensifier units including a pair of sequentially operated reciprocating ram assemblies powered by hydraulic cylinder motors which are operated to maintain a substantially uniform output fluid pressure from the intensifier unit. Each cylinder motor is supplied from a main source of hydraulic fluid under high pressure which operates on the working faces of the pistons of the cylinder motors. Hydraulic fluid is also supplied to the return face side of each piston in the hydraulic cylinder motor.

Abstract: A quadraplex pumping unit for use as a mud pump, an intensifier, or as a pump for abrasive fluids or the like includes four rams and four ram operating pistons. A control valve arrangement provides for pressure equalization and energy transfer from a cylinder which has just extended in a working stroke to a companion cylinder which has just returned to its retracted to rest position, to conserve energy and reduce the thermal burden on the hydraulic system. The valve arrangement further provides for prepressurization, after pressure equalization, prior to an extending stroke.