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| Aircraft Vacuum System Controller |
The engine driven pump sucks air through the system. The air flows in from the inlet filter, normally located under your instrument panel, directly into the inlet ports on your Artificial Horizon and Directional Gyro. The Suction Gauge is fitted between the Outlet and Inlet ports to give a differential pressure measured in Inches of Mercury. The Outlet sides of the Two Gyro’s are connected to a vacuum regulator which is used to regulate the amount of airflow measured on the suction gauge. Finally into the pumps vacuum port and the outlet port is vented under the cowling. In a turbine situation its very similar but vacuum is generated by means of Bleed Air.
Air-driven gyro instruments are designed to operate with a pressure differential of about 5 inches of mercury (about 2.5 psi). The pump is designed to produce plenty of airflow to spin the gyros even when the engine is idling on the ground. At normal flight RPMs, its capacity is much greater than necessary (as much as 20 psi). To maintain relatively constant airflow through the gyros, the regulator permits enough ambient air to leak into the system downstream from the gyros to limit the pressure differential across the gyros to about 5 in. Hg. The regulator is adjustable, and has its own foam air filter to protect the pump from contamination.
The cockpit vacuum gauge is connected to read the pressure differential across one of the gyro instruments (usually, the attitude indicator). The gauge normally has a green arc between 4.7 and 5.2 in. Hg. The vacuum regulator is adjusted so that the cockpit gauge reads about 5 in. Hg.
For more details, please go through the sources given. If you have any questions, please don't hesitate to ask me. Thanks.
https://www.experimentalaircraft.info/…/aircraft-vacuum-gyr…
https://www.flight-mechanic.com/sources-of-power-for-gyros…/
http://www.flightlearnings.com/2017/07/31/system-failures/
https://www.faa.gov/…/h…/aviation/phak/media/10_phak_ch8.pdf
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