A hydraulic liquid pressure sensor for use in a gas operated pressure sensor system includes a sensor body with a generally circular membrane resting surface, an inlet connected to a peripheral portion of the surface and an outlet opening from a central location on the surface. A flexible membrane is positioned adjacent to the resting surface and in flush contact therewith when not in use. The flexible membrane is secured and sealed around the periphery of the circular membrane resting surface. The inlet includes an annular groove in the pressure sensor body and spaced around substantially outward of the outlet opening. The inlet also includes an additional groove in the sensor body opening to the resting surface, connected to the annular inlet groove and extending inwardly therefrom.