suction relief valve

suction relief valve

suction relief valve
Wire screen.
A control valve that provides constant negative pressure by opening the system to the outside air when the vacuum rises above the preset value. Some gyro instruments (air-driven direction indicator, or DI, artificial horizons, etc.) are operated by air pulled into the instrument case by suction produced by an engine-driven vacuum pump, and a vacuum relief valve forms an integral part of the system.