Problems with Rapco dry vacuum pumps.

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

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

How about a slinger followed by a felt seal? The slinger can be made
from an o-ring. Felt will catch any tramp oil, is cheap, & can run dry.

If you have a homebuilt aircraft, consider this:

Pull the plugs from the engine. Put your ear on the pump. Have someone
slowly turn the prop. Listen to the vanes inside the pump fall from
the inside to the outside of the rotor slot. There should be a regular
"click" as each or the six, ( I think that there are six) vanes fall.

If you do not hear the vanes fall, they most likely are "hung up" due
to some contamination. Open the pump, and clean everything. Put it
back together. I use a little silicon seal to act as a gasket on the
back joint of the pump.
I think that the pumps fail when the vane gets sticky and refuses to
slide in and out of the slot in the rotor. I know that the slots in
the rotor will wear larger eventually, but I listen to my pump every
25 hours at the oil change and have had to clean the pump twice in the
last 250 hours. The pump now has about 800 hours on it.

Good luck.










On 21 Sep 2005 14:03:08 -0700, "nrp" wrote:

How about a slinger followed by a felt seal? The slinger can be made
from an o-ring. Felt will catch any tramp oil, is cheap, & can run dry.


Zenith CH-300 Driver.

Tim,

Wish you posted this before. I kind of suspected possibly cleaning it
but was afraid of messing it up. I sent it back to Rapco who refused to
warranty service it but gave me a discount deal on a new replacement
pump.

Tim Hickey wrote:
.....
If you do not hear the vanes fall, they most likely are "hung up" due
to some contamination. Open the pump, and clean everything. Put it
back together. I use a little silicon seal to act as a gasket on the
back joint of the pump.
I think that the pumps fail when the vane gets sticky and refuses to
slide in and out of the slot in the rotor. I know that the slots in
the rotor will wear larger eventually, but I listen to my pump every
25 hours at the oil change and have had to clean the pump twice in the
last 250 hours. The pump now has about 800 hours on it.
.....