Backup vacuum systems

Anyone have any experience with or comments about the manifold pressure
based standby vacuum system vs a separate electrical driven vacuum
pump? Other than the price difference. I want to install a backup and
am interested in getting some info.


Regards,
Jerry

wrote:
Anyone have any experience with or comments about the manifold pressure
based standby vacuum system vs a separate electrical driven vacuum
pump? Other than the price difference. I want to install a backup and
am interested in getting some info.

I have the precise flight vacuum backup which relies upon the difference
in manifold pressure Vs. static pressure. It was on the AC when I bought
it but since there is a wet vacuum pump on the AC (highly reliable) I'm
curious as to why it was installed. There are several ADs out for the
precise flight alternate vacuum system which makes it more of a PITA
than anything else but it does work and it is fairly fool proof. The
thing you have to keep in mind is that you have to have sufficient
difference MP VS static pressure so if you are up at altituded running
wide open and your pump fails you will end up having to decend to a
point where you can obtain this difference to run the gyros.

If it were me I'd put the extra coin into having an electrical driven
backup pump system.... especially if I did not have a wet pump.

ktbr wrote:

I have the precise flight vacuum backup which relies upon the difference
in manifold pressure Vs. static pressure. It was on the AC when I bought
it but since there is a wet vacuum pump on the AC (highly reliable) I'm
curious as to why it was installed. There are several ADs out for the
precise flight alternate vacuum system which makes it more of a PITA
than anything else but it does work and it is fairly fool proof. The
thing you have to keep in mind is that you have to have sufficient
difference MP VS static pressure so if you are up at altituded running
wide open and your pump fails you will end up having to decend to a
point where you can obtain this difference to run the gyros.

If it were me I'd put the extra coin into having an electrical driven
backup pump system.... especially if I did not have a wet pump.

Agree completely except for the electric pump backup. I'd rather an electric
powered AI.

I've owned the Precise Flight and it's OK for what it does, but it has too many
limitations for the price (both first cost and maintenance). Spring for an
electric AI.

Dave

My thinking is the electrically driven BU vac/pressure pump is 1st choice
for BU. This setup gives me my autopilot. If I only had the electric AI, I
have no A/P on failure. Yes, the electric AI is good 2nd BU for me.

Thx, {|;-)

Victor J. (Jim) Osborne, Jr.

ps: See thread in rec.av....ifr about my recent loss of BOTH primary and BU
on the same flight within 5 minutes of each other. Hence the Sporty's
electric AI on order.


I've owned the Precise Flight and it's OK for what it does, but it has too
many limitations for the price (both first cost and maintenance). Spring
for an electric AI.

Dave

Sporty's pilot shop has a nifty electric AI that can legally replace
your Turn Coordinator. That's the way I'd go if I hadn't already
installed an STEC in there.

The wet pump is another good alternative, though the gyros can still
fail.

I have Precise Flight. I think a recent install bypasses most/all ADs.

Clearly a backup pump or electric AI provides more at a comparable cost.

Whatever you do, have an idiot light that tells you something failed.
Precise Flight provides that and it may be as useful as the actual
backup if you otherwise don't have a light.

ktbr wrote:
wrote:

Anyone have any experience with or comments about the manifold pressure
based standby vacuum system vs a separate electrical driven vacuum
pump? Other than the price difference. I want to install a backup and
am interested in getting some info.

Paul kgyy wrote:

Sporty's pilot shop has a nifty electric AI that can legally replace
your Turn Coordinator.

I believe that this would be a risky choice, in that the Sporty AI can
tumble. It would be nasty to have a failure, enter an unusual attitude,
and then tumble your backup AI.

- Andrew

Maule Driver wrote:

I have Precise Flight. I think a recent install bypasses most/all ADs.

Clearly a backup pump or electric AI provides more at a comparable cost.

Whatever you do, have an idiot light that tells you something failed.
Precise Flight provides that and it may be as useful as the actual
backup if you otherwise don't have a light.


I also have a Precise Flight, installed in 1996. Mine was an SVS-III
which is the subject of the AD. Turns out if you have the later style
valve (sold since around 1992), it is just a paper work change...new AFM
supplement and a copy of the AMOC letter...to change it to an SVS-V in
order to terminate the AD. All the paperwork is available from the
website, so if you do the paperwork updates and show it to your A&P, it
should cost you nothing more than a box of donuts or six pack of beer.

What is the story with replacing the TC with an electric AI?

I thought that had been generally prohibited in most/all a/c. There was
an effort to change that but I didn't think anything had happened.

Paul kgyy wrote:
Sporty's pilot shop has a nifty electric AI that can legally replace
your Turn Coordinator. That's the way I'd go if I hadn't already
installed an STEC in there.

The wet pump is another good alternative, though the gyros can still
fail.

I had the Precise Flight in my Super Viking... We got into a situation
where the engine would suddenly go lean, pinning the EGT, causing me to
have to quickly go full rich (once I noticed), reduce throttle, then
reset and relean, or it would suddenly be running way rich making me
crazy... This came to a head after multiple episodes over 7 months with
the spending of thousands of dollars on multiple mechanics who couldn't
find anything wrong, and replacing the fuel injection pump ($0.7 AMU),
injectors, etc... Finally, it happened twice on a local flight and I
lost it mentally, landed, grabbed my wrenches, and began stripping
down the induction and fuel system.. Took me all of 25 minutes to find
it... The pivot pin on the flapper that selected between suction from
the pump or suction from the intake manifold had come out... The pin
and a ball bearing were gone, sucked through the engine... The flapper
was rattling around in the TEE valve and it would randomly block or
unblock the orifice to the intake, radically changing the mixture...

Precise Flight made sympathy noises and offered new parts at no cost
(and would I send in the old ones - didn't want the FAA seeing them)...
Of course, they had no interest in reimbursing me my costs... While I
replaced the defective parts I have no interest in having their sytem
on any planes in the future...

denny