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What is the typical normal value for vacuum pressure created by a vacuum pump?

  • A

    3 - 5 inHg

  • B

    3 - 5 hPa

  • C

    3 - 5 bar

  • D

    3 - 5 mmHg

Refer to figures.
The vacuum pump is an engine driven pump which creates a small suction pressure, to drive air through gyroscopic instruments. This spins up the gyros. The pressure difference created by the pump is not very high, and the normal in-flight value is typically 3 to 5 inches of Mercury (inHg). The figure shows the vacuum suction gauge for a Cessna 172, where the normal value is about 5 inHg. In a Piper PA28, the normal value is 4 inHg.

5 inHg is equivalent to about 170 hPa, or the pressure difference between sea level and 5000 ft.

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