Abstract: A hydraulic intensifier for oil well fracturing and/or erosion drilling incorporates a pair of intensifier units mounted on a common bed. The intensifier units are particularly defined for ease of maintenance in the field, and structure is provided by which the ram seals as well as the ram, the ram cylinder, and the hydraulic cylinder can be easily and readily removed in the field without the necessity for releasing the tension on the tie rods. To this end, the apparatus includes a front wall which supports the ram cylinder and an intermediate wall which supports the forward end of the hydraulic cylinder. The space between these walls and the manner in which the components are assembled permits the ram seal assembly, the ram and ram cylinder, and hydraulic piston to be extracted and reinserted. Also, an improved ram return system and a hydraulic cushioning system are disclosed.