Problems with Rapco dry vacuum pumps.

[abripl]

Just a warning for those who might consider purchasing Rapco dry vacuum
pumps. Make sure that your engine does not leak oil. If there is any
chance of an oil drip onto the Rapco vacuum pump it may eventually stop
working. The connecting shaft is vented to air. But if some oil drops
on the shaft it may get sucked into the pump and after the oil dries it
may seize the pump. I puchased a 216CW new pump from Spruce and after
20 hours of use it does not work. After returning it to Rapco they said
it was "oil contamination" and not eligible for warranty service, but
offered to replace it at a discount. They really ought to have a better
seal there to prevent the problem.

[Newps]

If you were really smart you would have ditched your pump and installed
the Aeon pump instead. More expensive than the normal dry pump but the
next best thing to a wet pump.



abripl wrote:
> Just a warning for those who might consider purchasing Rapco dry vacuum
> pumps. Make sure that your engine does not leak oil. If there is any
> chance of an oil drip onto the Rapco vacuum pump it may eventually stop
> working. The connecting shaft is vented to air. But if some oil drops
> on the shaft it may get sucked into the pump and after the oil dries it
> may seize the pump. I puchased a 216CW new pump from Spruce and after
> 20 hours of use it does not work. After returning it to Rapco they said
> it was "oil contamination" and not eligible for warranty service, but
> offered to replace it at a discount. They really ought to have a better
> seal there to prevent the problem.
>

[abripl]

> ...you would have ... installed the Aeon pump instead
Actually I removed the vac pump and went to all electric - saved some
weight. But I do think that Rapco or any mfg should prevent something
like that with a seal.

Did you check the Aen pump for oil drip problems? Do they warranty
against oil entry?

[[email protected]]

Rapco can't put any serious seal on that pump that would last any
time because it's a dry pump, and seals need some lube. Rapco does have
a pump to fit the under-nose mountings like the O-200, where oil tends
to get into the pump, and that pump has a flinger and a drain port to
keep oil out.
Washing the engine with solvent can also wreck the pump. It
needs to be covered during spraydown.
We use Rapco pumps exclusively on five airplanes, and have no
trouble at all reaching 1000 hours.
Basically, your oil leak need fixing. Oil leaks represent an
attraction for dirt, which does no engine any good, and they're a fire
hazard. And some oil leaks are warnings to fix something before it
blows off completely and all the oil is lost overboard in flight.

Dan

[abripl]

> Rapco can't put any serious "seal" on that pump...
> ... [They have a]... pump has a "flinger and a drain port" to keep oil out...
I don't care what its called - it should be on there. Is the
manufacturing cost of such feature so significant? I don't recall any
warnings that came with my new Rapco pump about simple oil drip hazards
or about a special pump model required. I only found out when warranty
service was denied.

> ...Basically, your oil leak need fixing.....
No kidding. But while you are trying to fix it or if you are unaware of
oil leaks you take a flight risk with the pump. Engines can START
leaking and ruin these "sensitive" pumps. A lot of homebuilders, like
me, have initial leaks until they are found and fixed - its not a lack
of trying.

This post is a warning to others about the risk they may take with such
pumps - unless they are 100% sure their engine does not leak and never
will leak. Even if they find/fix the leak quickly they will not know if
the pump is OK, since the pump tends to work for a while after oil gets
in there.

[NW_PILOT]

"abripl" > wrote in message
oups.com...
> > Rapco can't put any serious "seal" on that pump...
> > ... [They have a]... pump has a "flinger and a drain port" to keep oil
out...
> I don't care what its called - it should be on there. Is the
> manufacturing cost of such feature so significant? I don't recall any
> warnings that came with my new Rapco pump about simple oil drip hazards
> or about a special pump model required. I only found out when warranty
> service was denied.
>
> > ...Basically, your oil leak need fixing.....
> No kidding. But while you are trying to fix it or if you are unaware of
> oil leaks you take a flight risk with the pump. Engines can START
> leaking and ruin these "sensitive" pumps. A lot of homebuilders, like
> me, have initial leaks until they are found and fixed - its not a lack
> of trying.
>
> This post is a warning to others about the risk they may take with such
> pumps - unless they are 100% sure their engine does not leak and never
> will leak. Even if they find/fix the leak quickly they will not know if
> the pump is OK, since the pump tends to work for a while after oil gets
> in there.
>

Any good mechanic can find an oil leak its not that hard.

[abripl]

? Any good mechanic can find an oil leak its not that hard.

You miss the point. After you find it, it may already be too late
because the oil might have leaked on the pump. So anytime you discover
a (new) leak you cannot be sure that the pump was not contaminated. The
only sure way is to replace the pump. This is not necessary if Rapco
designed the pump to reject accidental oil spillage.

[Jonathan Goodish]

In article . com>,
"abripl" > wrote:
> You miss the point. After you find it, it may already be too late
> because the oil might have leaked on the pump. So anytime you discover
> a (new) leak you cannot be sure that the pump was not contaminated. The
> only sure way is to replace the pump. This is not necessary if Rapco
> designed the pump to reject accidental oil spillage.

As far as I know, engines shouldn't leak oil in this location, so why
would Rapco or anyone else waste time designing a pump that is immune to
it? It seems that the solution would be to fix the real problem, the
oil leak, and simply replace the (relatively inexpensive) pump.

If you don't know how to fix the oil leak the first time, you may want
to consult with an experienced mechanic.


JKG

[abripl]

> ...engines shouldn't leak oil in this location...
What location? Did I mention a location?

> why would Rapco ... waste time designing a pump that is immune to it
In fact if you read Dan's above post they do design pumps imune to the
problem.

And you still miss the point. You can develop an oil leak and not know
it for a while... Then you are at risk flying your bird....

> It seems that the solution would be to fix the real problem, the
> oil leak, and simply replace the (relatively inexpensive) pump....
Well at least now you concede the necessity of having to replace the
pump - irregardless of whether I do it or a mechanic.

> If you don't know how to fix the oil leak the first time... etc...
My skill is not the issue here.... you don't know what it is, it could
be better than a certified mechanics.

[[email protected]]

> My skill is not the issue here.... you don't know what it is, it could
> be better than a certified mechanics.

You could have Googled and found this:

http://www.casa.gov.au/airworth/aac/PART-1/1-098.HTM

A government document that speaks of solvent and oil
contamination of Edo (now Sigma-Tech) and Airborne vacuum pumps.
Apparently Rapco doesn't have the only pump that can't keep out oil. As
I said, those dry pumps are limited in the sealing out of oil, since
the sort of oil seal needed needs oil to survive.

Another article:
http://www.seqair.com/skunkworks/Maintenance/VacuumPump/VacuumPump.html

Better fix that oil leak.


Dan

[abripl]

Google for what? You must have diligently spent time looking for the
first link (or are you from Australia). Not easy to find.

Here is an interesting extract from it (the second link is not all that
useful)
"...dry vacuum pumps .... have been a source of continual premature
failure...."

> Better fix that oil leak.
Who said I didn't? But you still refuse to acknowledge the point that
an oil leak could develop that you or your mechanic DO NOT KNOW ABOUT
and you are taking a risk. And as you said, Rapco (and others) already
know how to fix the problem.

[flybynightkarmarepair]

> Who said I didn't? But you still refuse to acknowledge the point that
> an oil leak could develop that you or your mechanic DO NOT KNOW ABOUT
> and you are taking a risk. And as you said, Rapco (and others) already
> know how to fix the problem.

With enough money, MANY (but not all) problems can be solved. The
amount of money needed may exceed the utility gained by doing so This
is going to get a little long-winded, so bear with me.

Dry vacuum pumps are mounted either vertically, as in the O-200, or
horizontally, as in most every other engine generally encountered. The
oil that gums up the vanes and causes them to snap probably leaks from
the accessory case shaft. If the vacuum pump is mounted vertically,
you've got a problem - seals drip, even good ones, so oil WILL migrate
towards your pump shaft, maybe a little, maybe a lot, but it happens
ALL THE TIME. But the key to a solution lies within the problem itself
- you have a RELIABLE source of oil to keep the seal on the vacuum pump
happy. Your goal is to essentially regulate the amount of oil that
gets INTO the vacuum pump to a slight sheen on the input shaft and no
more. Between the flinger and the seal, you can do that. (Even so,
I'll bet the life of vacuum pump on a C-150 is, on average, less than
that on a C-172 - those of you with maintenance experience in training
fleets can shout me down on this if you know better)

Mount the accessory drive and the vacuuum pump horizontally, and you no
longer have access to this solution. You no longer have a reliable,
everyday source of oil to lubricate the seal that "abripl" thinks
should be there on the input shaft of the pump (some oil may creep
along the shaft, but gravity is taking most of it down toward the
ramp). If you put one there anyway, it would burn up in a few hours
running dry on the steel shaft, and wouldn't be there when you REALLY
needed it, for the non-standard rate of leakage out of the accesssory
case or wherever.

There are seals that will run dry. Some exotic elastomers claim they
can, as lip or face seals, but life is short even then. A labyrinth
seal, as used in steam turbines, might do it, but they require
exquisite precision not just in the seals themselves, but also in the
bearings that support the shaft.

The engineers at Rapco, and Edo designed their pumps for the
application at hand with a compromise between cost and risk, and given
that Nature Abhors a Vacuum, it's a friggin' marvel they work as well
as they do, as long as they do, for as cheap as they are.

[[email protected]]

>Who said I didn't? But you still refuse to acknowledge the point that
>an oil leak could develop that you or your mechanic DO NOT KNOW ABOUT
>and you are taking a risk. And as you said, Rapco (and others) already
>know how to fix the problem.

Listen: the vacuum pump has an open frame between the drive
input and the pump itself. Oil has to get into this space to get past
the pump's seal. Oil getting into this space is also going to be
apparent as a mess on the engine, inside the cowling, on the belly, and
on the ground. I work on these things every day (I suspect you don't)
and I won't tolerate leaks that present any hazard to any component.
The oil coming off the engine crankcase breather is bad enough for me.
Oil ruins wiring harnesses, air hoses, steering rod boots, ignition
leads, magnetos, alternators, and vacuum pumps. Get ready to spend more
money.
Some people won't take advice and suffer the consequences,
wondering why the bad stuff always happens to them. I spent 12 years
remanufacturing air brake components for heavy trucks and industrial
machinery, and most of the warranty comebacks followed the same
pattern: control valves full of dirt, compressors destroyed by dirt
getting past old filters or through a lack of oil pressure when the
mechanic used a bunch of silicone to seal a fitting, thereby plugging a
gallery, or chunks of rubber from rotten hoses fouling things up. The
same things happen to aircraft vacuum pumps: dirt, carbon in the hoses
from the last blow-up pump, bits of rotten hose liners, ancient and
crumbling relief valve filter media, or oil from unrepaired leaks; all
stuff allowed into them that has no place there. We used to put
instructions in every box, with every air brake component, telling the
mechanic what to watch for if he wanted the thing to work right the
first time and for a long time. It was a free education that most
refused, and we were forever trying to convince them to clean up the
factors that caused the failure of the original component and
necessitated the replacement in the first place. They just kept
replacing stuff, usually at our expense. They didn't gain much respect
as mechanics.
What killed your original vacuum pump? You seem to be missing
the point that a successful seal that would keep oil out of a pump is
the sort of seal that would need oil to keep it alive. The vacuum pump
seals are designed to run dry and are not the type of seal that can
keep significant quantities of oils out. Seal technology is a whole
science of its own, and there is no single seal that can cover all
possible applications.
Aircraft maintenance includes making sure there's a good air
cleaner to keep dirt out of the engine. It should also include making
sure oil leaks aren't bothering your pump.
Dan

[[email protected]]

>Google for what? You must have diligently spent time looking for the
>first link (or are you from Australia). Not easy to find.

Took two minutes. I Googled "Airborne Vacuum pumps."
Edo/Sigma-tech and Airborne built vacuum pumps for aircraft. You'd have
to be in the industry to know that, I suppose.

Dan

[rons321]

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

[[email protected]]

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

[abripl]

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.

[nrp]

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.

[Tim Hickey]

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.

[[email protected]]

>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

[[email protected]]

>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.

The felt will wear. It's used in many older aircraft wheel
bearings (even some newer ones, and it doesn't work that well. It has
to be saturated with grease to prevent water uptake, and thereby
attracts dust. If it soaked up oil it would become saturated and allow
the oil past.
Autos and trucks abandoned felt seals in the '40s and '50s.

Dan

[abripl]

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?...

[Reggie]

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

[[email protected]]

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]

> "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

[abripl]

> 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

[Reggie]

MAGNETIC pump drive

>From:
>Date: 23 Sep 2005 08:31:24 -0700
>Local: Fri, Sep 23 2005 8:31 am
>Subject: Re: 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/dfx/archives/0303/0303justonemore.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

[[email protected]]

You're right. There would be plenty of torque transfer available for
a vacuum pump. Now someone needs to try it.

Dan

[abripl]

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.
>.....