Unusual Vacuum system indication, please help explain.

[Al]

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 :) )

[[email protected]]

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?

[Al]

> 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.

[[email protected]]

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.

[Al]

Hmmm, the little red pins on the gauge that stuck out when stopped, and
retracted when we started, said "Vacuum Source". We didn't have vacuum pumps
on the Lear, but did on the C-340.

Al G.

"karl gruber" > wrote in message
...
> All the pressurized airplanes I've flown have "pressure" not vacuum
> systems.
>
> Karl
> ATP, CFI, ETC
> "Curator" N185KG
>
>
> "Al" > wrote in message
> ...
>> 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 :) )
>>
>
>

[swag]

I know the guage in the P337 looks like the guage on the Bonanza I used
to fly--and that had a pressure pump. The pins would pop out if the
pump didn't deliver enough pressure.
I fly a P337 and should know if it has vacuum pumps or pressure pumps,
but I don't (red face)
Al wrote:
> Hmmm, the little red pins on the gauge that stuck out when stopped, and
> retracted when we started, said "Vacuum Source". We didn't have vacuum pumps
> on the Lear, but did on the C-340.
>
> Al G.
>
> "karl gruber" > wrote in message
> ...
> > All the pressurized airplanes I've flown have "pressure" not vacuum
> > systems.
> >
> > Karl
> > ATP, CFI, ETC
> > "Curator" N185KG
> >
> >
> > "Al" > wrote in message
> > ...
> >> 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 :) )
> >>
> >
> >

[Al]

So, even if it had a pressure pump, wouldn't the original question be the
same? i.e. How does a failure(open) in the system produce a high
Vacuum/Pressure?

This is kind of embarassing for someone like me who "knows everything". :)

Shields are up, captain.

Al G



"swag" > wrote in message
ups.com...
>I know the guage in the P337 looks like the guage on the Bonanza I used
> to fly--and that had a pressure pump. The pins would pop out if the
> pump didn't deliver enough pressure.
> I fly a P337 and should know if it has vacuum pumps or pressure pumps,
> but I don't (red face)
> Al wrote:
>> Hmmm, the little red pins on the gauge that stuck out when stopped, and
>> retracted when we started, said "Vacuum Source". We didn't have vacuum
>> pumps
>> on the Lear, but did on the C-340.
>>
>> Al G.
>>
>> "karl gruber" > wrote in message
>> ...
>> > All the pressurized airplanes I've flown have "pressure" not vacuum
>> > systems.
>> >
>> > Karl
>> > ATP, CFI, ETC
>> > "Curator" N185KG
>> >
>> >
>> > "Al" > wrote in message
>> > ...
>> >> 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 :) )
>> >>
>> >
>> >
>

[John R. Copeland]

All the Cessnas I've flown, both pressurized and non-pressurized,
have always used vacuum systems for gyro supply.
My non-pressurized 337B used vacuum, so I'd expect P337s do too.
(Beechcraft has used pressure systems for a long time, however.)

"swag" > wrote in message ups.com...
>I know the guage in the P337 looks like the guage on the Bonanza I used
> to fly--and that had a pressure pump. The pins would pop out if the
> pump didn't deliver enough pressure.
> I fly a P337 and should know if it has vacuum pumps or pressure pumps,
> but I don't (red face)
> Al wrote:
>> Hmmm, the little red pins on the gauge that stuck out when stopped, and
>> retracted when we started, said "Vacuum Source". We didn't have vacuum pumps
>> on the Lear, but did on the C-340.
>>
>> Al G.
>>
>> "karl gruber" > wrote in message
>> ...
>> > All the pressurized airplanes I've flown have "pressure" not vacuum
>> > systems.
>> >
>> > Karl
>> > ATP, CFI, ETC
>> > "Curator" N185KG
>> >
>> >
>> > "Al" > wrote in message
>> > ...
>> >> 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 :) )
>> >>
>> >
>> >
>