Abstract: An apparatus for protecting a pressure differential sensor from exceeding a maximum allowable pressure differential. The apparatus has a housing which has a low-pressure chamber and a high-pressure chamber. A pressure-sensitive member separates the high-pressure chamber and the low-pressure chamber from one another. A blocking member is provided for blocking the entrance of fluid into the high-pressure chamber in response to the pressure-sensitive member sensing an initial differential pressure between the high-pressure chamber and the low-pressure chamber which exceeds the maximum allowable differential pressure. There may also be provided equilibration structure for creating a hysteresis loop as to the magnitude of the pressure differential between the high-pressure chamber and the low-pressure chamber.