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Old June 12th 06, 06:58 PM posted to rec.aviation.ifr,rec.aviation.piloting
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Default Unusual Vacuum system indication, please help explain.

On Mon, 12 Jun 2006 10:06:47 -0700, "Al"
wrote:


wrote in message
.. .
On Mon, 12 Jun 2006 09:34:18 -0700, "Al"
wrote:

Hi Group.

I had a trip Friday in a 1977 C-337G(pressurized). On the taxi out I
noticed the suction gauge was pegged high. The AI erected ok, but the DG
required many updates on the way to the run-up area. Pulling on to the
runway, we corrected the DG again, by 30 degrees.
We flew VFR to Boise, and checked out the new Garmin 530 just
installed.
Once we got on the ground, the avionics guy, we had along, pulled the
access
panel in front of the left windshield. On the back of the panel there is a
component that looks like the back of an altimeter, only about half as
deep.
It has a tube labeled "Air IN" and this one had no hose attached. Nearby
was
a loose hose, which we reconnected. The system worked fine, and we had no
more problems.
Can anyone explain to me how opening a fault anywhere in vacuum system
can deliver a high vacuum? The gauge worked normally, low before start,
rising when the engine lit off. Two source indicators both showed a
working
pump on each engine. I assume the component I was looking at was a
regulator, but I fail to see how the fault we found, could give us the
indication we saw.

Al G (There is another Al on the goup now )


What would the effect be of a byepass valve?


Wouldn't that bleed air into the system, thereby reducing the vacuum?

The only system I've ever seen that had high vacuum was in an old 182 flown
by a heavy smoker. The filter was plugged. Even that system wasn't pegged.

Al G.


I'm only trying to guess!

If the byepass valve does not detect a high differrential pressure
wouldn't the vacuum be at maximum? Is it a one way valve so that there
is no leak at the other end?

An interesting problem.