A pressure control apparatus suitable for controlling pressures in autoclaves permits a plurality of autoclaves (1 - 8) to be selectably pressurized from a single pressurizing circuit (30,32,34,36). The apparatus can be externally controlled (4) to more efficiently multiplex autoclaves to the pressurizing circuit and to more efficiently implement different pressure schedules for the autoclaves. Once a pressure has been set for an autoclave maintained in communication with the main pressurizing circuit, the apparatus automatically monitors the position of the pump piston (34) and resets it from either of its extreme limits of movement to maintain pressure at a desired set point.