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enter image description here

This is one of the examples of a pneumatic power system in a multi-engine airplane. In systems like this, if one dry air pump fails - let's say the right-hand one - then the check valve manifold closes the right-hand part of the system. I can understand this and it makes sense, but I can't understand how the check valve manifold works.

I already went through an aircraft maintenance manual which has kind of this system, but I can't find any clue. My instructor guesses that inside the check valve manifold there's some kind of shuttle valve. But I don't agree with this. Could someone help me out to understand?

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  • $\begingroup$ It is probably like any other check valve, it has a spring operated "ball" that seals when pressure on one side allows the spring to expand and push the ball against the seals. I don't have a diagram of the valve (hence not an answer), but that seems plausible. $\endgroup$
    – Ron Beyer
    Aug 2, 2018 at 0:34
  • $\begingroup$ I agree with you, but I want know what exactly happen inside. I know this is too much for pilot though. $\endgroup$
    – Red Ananas
    Aug 2, 2018 at 1:09
  • $\begingroup$ Also, it should be noted that vacuum driven gyro's are commonly being replaced with electronic instruments. As an example, a pair of Garmin G5s in place of the attitude indicator and the directional gyro. That would simplfy the diagram some. $\endgroup$
    – CrossRoads
    Aug 2, 2018 at 11:51

1 Answer 1

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On each side of the check valve manifold there is a check valve that only allows air to flow toward the vacuum pump on that side. For the left pump, the check valve is the rectangular bit between the far left line going to the vacuum gauge and the adjacent line going to the deflate valve, and for the right pump it is between the far right line and the gyro suction line.

The result is if one vacuum pump no longer is producing suction, the vacuum gauge indication on that side, being "upstream" of the check valve now that only the opposite pump is pulling air, will show no vacuum; meanwhile the operating pump can still pull air through the other three lines and can still operate the deflate valve and vacuum gyros. Its vacuum regulator will control the vacuum level. Everything will continue to work normally with only the loss of vacuum indication for the failed pump providing an indication that something is wrong.enter image description here

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