Harmon Technologies, Inc.

Vacuum Gauge

The vacuum gauge shows how much suction is available to drive the vacuum powered gyro instruments.  Normally, it should be about 5 psi.  The vacuum system is powered by a vacuum pump connected to the engine.  These pumps can fail and if they do, important vacuum powered gyros (such as the attitude indicator) could stop working.  While pilots are trained to handle this situation, some aircraft (such as N4907J) have also installed backup vacuum systems that can take over the job.  Should the engine powered vacuum pump fail, this guage will confirm the issue and a "low vacuum" warning light will illuminate in front of the pilot.  The pilot can then activate the backup system that uses engine manifold pressure to provide vacuum.

During the preflight cockpit check, this gauge is used to confirm proper primary and backup system operation.

Copyright © 2004 Harmon Technologies, Inc.