negative pressure relief valve

negative pressure relief valve

The cabin-air pressure safety valve combines functions of over-pressure relief valve, vacuum relief valve, and dump valve. Over-pressure relief valve prevents cabin pressure from exceeding specified values; vacuum relief ensures that ambient air pressure is less than cabin pressure by allowing ambient air to enter cabin whenever ambient air exceeds cabin pressure; while dump valve permits depressurization of cabin by cockpit operated switch.A relief valve in an aircraft pressurization system that prevents the pressure in the cabin from becoming lower than the ambient outside pressure.