Abstract: Two hydraulic pressure intensifiers are coupled in parallel between a source of hydraulic fluid at relatively low pressure and an output path. Each intensifier provides a pressurizing stroke in only one direction of linear reciprocation. The intensifiers are so operated, under the control of a hydraulic circuit, as to create a tendency for an initial portion of the pressurizing stroke of each of the intensifiers to overlap a final portion of a preceding pressurizing stroke of the other intensifier, and thereby to deliver high pressure hydraulic fluid to the output path simultaneously with continuing delivery from such other intensifier. Such simultaneous delivery does not actually occur, however, since the hydraulic circuit is so arranged that the delivery of high pressure hydraulic fluid from each intensifier to the output line can begin only upon a falling off in the pressure provided by the other intensifier.