This apparatus, originally designed for soil mechanics test applications, can also be used to provide an infinitely variable constant pressure and is used in conjunction with the Hoek cell (see Hoek cells and sample extruder) fit with the permeability end caps, for the investigation of the permeability of rock at high confining pressure, in the laboratory. The apparatus comprises: motorized hydraulic pump honed piston/spring assembly precision test gauge 0-3500 kPa range cylindrical oil/water interchange vessel valves 2 kg of high viscosity oil