Problems with Rapco dry vacuum pumps.

rons321 wrote:
I agree with you. I am in the vacuum pump business, and I don't
understand why they can't make the pump a little more reliable. I can't
change the pump design myself, because it is certified the way it is.
It would be to costly to redesign it. If you need any vacuum pump
assistance, you can call me at 800-621-2531. Good luck to you. Ron

I would bet that any seal material or design that might work,
if it exists, would be so expensive that the pump price would rise just
enough that it would lose its competitive place in the market. Or if
there WAS a suitable seal, someone would have incorporated it by now
and marketed their pump as a superior, new and improved, longer lasting
oil- and solvent-proof design. Rapco HAS made small changes to their
pumps, things that weren't part of the original certification, such as
cooling fins, the inclusion of a small amount of salt in the vanes to
absorb a small amount of moisture and increase the vane life (low
humidity increases vane wear), and the flinger/oil drain idea for the
Continental vertical mount. Such changes lead me to believe that the
ideal shaft seal isn't available or affordable.

Dan

What I have learned from these posts is that dry vacuum pumps are a lot
more problematic than just the oil leak - as per
http://www.casa.gov.au/airworth/aac/PART-1/1-098.HTM link. Its too bad
that there is not more warnings before purchase instead of "wonderful"
features. The one hard to find link is hardly a help for a homebuilder.
I have perused these newsgroups frequently during building process and
there is hardly anything mentioned about inherent dry vacuum pump
problems. EAA has homebuilder vacuum systems help article
http://members.eaa.org/home/homebuilders/building/instruments/A%20Gyro%20Instrument%20System_%20(Your%20Options) .html#TopOfPage
with no operational warnings mentioned as in first article. I suspect,
Dan, that you are not a builder but either a certified plane pilot or
A&P making a living from repairs.

I have eventually replaced the vacuum system with electric for about
the same price and saved weight and expect a lot less problems.

I suspect,
Dan, that you are not a builder but either a certified plane pilot or
A&P making a living from repairs.

Close, but not quite:
-Canadian Aircraft Maintenance Engineer (AME) M1
-Commercial Pilot, Instructor rating
-Homebuilder: building or restoration projects have included
Taylor Monoplane, AMF-S14, Jodel D-11. Auster VI restoration project.
-Since 1972 in homebuilts, flying since '73

I currently spend most of my time in the shop maintaining
aircraft, but make no extra money from doing more work. I work in a
College-based flight training program and teach a class on Aircraft
Systems; between the maintenance and the teaching I have plenty of
reason for research into aircraft problems. When I'm not doing that I'm
flying, either to figure out some problem, or with a student, which
isn't too often anymore, or in the Jodel.

What's your experience?

Dan

Me,

I am (was) a kit builder. 200hrs PPL, now flying the
completed kit 18 months, 84hrs. Guess thats why
I am complaining since there was little "bad"
vacuum pump info available to me as a builder.
I do have a science/engineering background.
Hey, I am also a fellow Canuck but living in US now.

Wish I had the money back for all things I tried
that didn't work out as well.
------------------------------------------------
SQ2000 canard: http://www.abri.com/sq2000


wrote:
....
What's your experience?...

If the pump ran for the life of the engine TBO, who
would make money on that!!!!!

For a sealless drive use a magnetic coupling similar
to:

http://www.micropump.com/tech_tips/magnetic_drives.asp

Reggie

It would be nice to use a magnetic coupling, but the power
transfer in these pumps is too much. The mag coupling has been around
for years and the vac pump manufacturers would be aware of it. Another
problem with magnets: they'd be close to the magnetic compass, being on
the back of the engine in most cases, and we have enough trouble with
magnetic fields as it is when we go to calibrate compasses.
"abripl"'s solution of an electric drive, especially if it's
away from the engine, is alright as long as he doesn't intend to fly
IFR, unless he has a vacuum-driven turn coordinator. Most TCs are
electric, and with attitude and heading gyros relying on an electrical
source all attitude info would be lost if the electrical system quit,
which they can do at the worst possible times. I haven't yet dealt with
the new glass panels, but would hope that they'd have some backup
power; the ones I see have peanut gyros in the panel as backups.

Dan

"abripl"'s solution of an electric drive, especially if it's
away from the engine, is alright as long as he doesn't intend to fly
IFR, unless he has a vacuum-driven turn coordinator.

Actually it was not a solution for my vaccum pump but I simply went to
an electric horizon - removing the vacuum. I only use the electric
horizon (plus altimeter and speed ind.) as backup. I use Dynon's
EFIS-D10 for my primary flight instruments - and have the necessary IFR
certifications. You can see the panel on bottom of
http://www.abri.com/sq2000/choices.html

Most TCs are electric, and with attitude and heading gyros relying on an
electrical source all attitude info would be lost if the electrical system quit,

Oh that. I have a dual battery system and my EFIS-D10 has its own
internal backup battery to last an hour. The dual batteries have
40amp-hour total capacity and normal flight current is only about 12A.
Read more details at http://www.abri.com/sq2000

MAGNETIC pump drive

From:
Date: 23 Sep 2005 08:31:24 -0700
Local: Fri, Sep 23 2005 8:31 am
Subject: Problems with Rapco dry vacuum pumps.
Dan wrote:
It would be nice to use a magnetic coupling, but the power
transfer in these pumps is too much. The mag coupling has been around
for years and the vac pump manufacturers would be aware of it. Another
problem with magnets: they'd be close to the magnetic compass, being on
the back of the engine in most cases, and we have enough trouble with
magnetic fields as it is when we go to calibrate compasses.

Dan

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
http://www.manufacturingcenter.com/d...ustonemore.asp

The drives are manufactured by MagnaDrive Corp, Seattle, WA. Suited for
motors from 10 to 1000 hp, the company's drives and couplings,
according to Ron Woodard, MagnaDrive president and CEO, "also
eliminate hard starts and much
of the vibration associated with power transfer, allowing M-I/SWACO to
redesign their oil centrifuges with fewer control systems and with a
smaller footprint."
**********************
THEREFORE Dan,
Your torque limit is a design / weight problem, not a technology
limit. (Reggie)
************************************************** *************************************
http://www.sacskyranch.com/rapco.htm

The Edo(or Sigma-Tec) quill-shaft is designed to fail at 100
inch-pounds of torque,
whereas
Airborne drive takes (250 inch-pounds) to snap .

Therefore it's not a lot of torque required, and you would not
need the break away coupling as the magnetic field does that....
(Reggie)
************************************************** ***********************************

As far as the magnet compass problem
Beware of:
Alternators, especially permanate magnetic ones.
Elecrtic gyro instruments.
Too closely placed electric vaccuum pumps
and
Magnetized steel air frame structure.

Reggie