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Oil in Standby Vacuum Pump???


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'97 Encore with electric standby vacuum pump located in the avionics bay.

The standby pump recently failed during preflight run up checks.   Disassembled the pump and found oil in the pump which had caused stuck vanes in the rotor.   The inside of the pump was oil wet.

Where did the oil come from?      The primary engine driven is a dry vacuum pump.    Apparently there is enough oil in the line from the manifold where the two pumps connect  to the standby pump to cause problems.

Any ideas on the source of the oil?   I typically only operate the standby pump during preflight run up checks only.    How could engine oil get past the primary pump, not foul it and contaminate the standby vacuum system?  

Bill

 

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Bill, I'm curious about this too, because I had the exact same issue in my Ovation.  The pump that was originally installed when the plane was new got fouled with some sort of sticky wax-like substance a few years ago.  I replaced it with a new pump and on occasion have found oil in the pump's suction line.  It wasn't engine oil though as it was very clear.

Edited by Greg_D
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Some particular detail seems to be missing...

in all engines the engine oil is kept separate from the vacuum pump or the oil would get drawn into the pump and thrown into the pump's exhaust...

check each pump's exhaust tube and see what is coming out of it?

It is pretty easy to check the back-up vac pump exhaust tube(?), in the back of the LB...

There are some wet pumps being used.  Wet pumps have their own oil in them.

Some PP thoughts only.  Not a mechanic.

Best regards,

-a-

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14 hours ago, Mooney time said:

Experienced the same problem in my O.  We replaced the vacuum line going from the shuttle valve to the stand by pump.  Instruments weren't affected, but your right. It's a mess and you'll go thru a bunch of pumps. 

What was the source of the oil?

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8 hours ago, wpbarnar said:

Greg_D

What year model is your aircraft and approximately when did you have your problem?

Bill

It's a 1994 Ovation.  The original standby vacuum pump failed a couple of years ago and I replaced it then.  I first noticed the oil in the line a few week ago during the annual inspection.  I was able to get most of it out, but I'm concerned about where it is coming from.  And more concerned that it will cause the standby system to fail when I need it most.  Like you, I run it on the ground mostly, before takeoff.

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I believe the source of the oil is the hose itself.     The hose from the manifold under the glare shield to the standby vacuum pump is made of some type of vinyl.  I think it is slowly breaking down due to its age.   Over time,  a small quantity of oil accumulates in the hose and migrates toward the standby pump.

Key findings that lead to my belief:

The vinyl hose feels oily or greasy to the touch.

The oil in the pump suction was clear, not engine oil.

I have thoroughly inspected all the other vacuum system components. The only place I found evidence of oil contamination was in the vinyl hose and S/B vacuum pump.   There is no plausible method for oil to enter system. 

Both "Mooney time" and "Greg_D" experienced a similar problem.   All three aircraft are roughly the same age.   The problem occurs about +20 years in service.  Either it is the vinyl material used in that era or the vinyl hose starts breaking down after a period of time.
 

If it can be done as a minor modification,  I plan on installing a CV1J4 filter which is identical to the filter that protects the primary vacuum pump.  This is only a stop gap measure until there is a suitable time to replace the hose.

Bill
 

 

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Bill,

That is an interesting theory.  I've noticed that the hose feels very oily as well.  I will see if I can get some pictures soon.  In the meantime, the attached pictures are of the old pump.  Whatever caused it to fail was not a clear liquid.  It appeared like someone used thread lubricant during assembly, which then got to the pump internals.

 

 

IMG_20140705_173751.JPG

IMG_20140705_173729.JPG

IMG_20140707_120501.JPG

IMG_20140707_120444.JPG

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Could that be a slurry like mixture of graphite from the vanes and the oil?

The clear oil I saw was just prior to the pump inlet.    Internally in the pump it was dark and dirty.    

I also had some of that paste like material in the ports.

Your hose is identical in appearance.  I wonder if they are that same color when new?

Bill

image.jpeg

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I was thinking these were going to look more like the O2 system PE tubing with fittings.  Flexible tubing made from PVC may be a challenge to keep from collapsing...

PVC tubing usually starts life as being very clear and turns hazy and brown over time...  PVC can be colored as part of the process it goes through in manufacturing...

When making the tubing flexible, they compound in a chemical simply called a plasticizer...

See this site for insight on PVC and its plasticizers...  http://www.pvc.org/en/p/plasticisers I believe the pthatlates are typically oils.  A known example of pthalate migration is on car instrument panel tops visors (name for that thing? We have them in Mooneys) the pthalates get heated by the sun and deposit on the inside of the windshield.  This is a messy challenge to clean properly.

I remember seeing rubber hose that is multilayered with fibers to provide some rigidity. I don't recall any clear tubing where my back-up pump is in the tail...  '94 O...

Intersting, you guys may be onto something...!

Best regards,

-a-

Edited by carusoam
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Yes it is a 2000, yellow tube identical.  It felt oily on outside and inside identical to what is previously described.  Don't know how hard to replace that tube....probably a PITA.  I wonder how long a filter would last, aren't most of them designed for dry material.  I would think an oil would clog it up.  Going to make a call tuesday to Mr. Maxwell.

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1 hour ago, carusoam said:

Expect the air filter to be similar to a coffee filter.  Not going to hold back any liquids it encounters...

Replacing that tube looks like it has to go a long distance.

 

Best regards,

-a-

You have to pull all the lower left side interior.

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  • 4 weeks later...

Well spent several hours removing the interior panel, what a PITA.....traced the hose up into the bowels of the instrument panel where it's termination is hidden by lots of wires, cables, instruments, etc.. Any advice on how to to go about getting to  to the end?  

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Have you removed the glare shield on top of your panel?     Access to where it connected to the manifold was from the top on my K model.   It is behind the attitude indicator on the fire wall.   

I was tempted to remove the AI for better visibility  but managed without doing so.

Bill

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I should have taken a picture.....The Moritz engine clusters are reasonably deep and hide a lot as well.  I have an Ovation so don't know how common the plumbing and wiring is back there to a K.  I assume the hose ties into some type of manifold but it is a mess of stuff underneath there and the yellow hose just disappears into a mass of wires.

 

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After determining the degrading Tygon tubing in my standby vacuum system was the problem, I replaced it  with Aeroquip 306 (MIL-H-5593) due to concerns of damaging another vacuum pump.   Now I am really glad that I did.   The old tubing showed evidence of its oil or plasticiser attacking other plastic pieces that it was in contact with.   Surely the long term effects of being in contact with wiring insulation would not be healthy.  See the attached photo with the imprint of a tyrap on the Tygon hose.  

I have learned a lot since my first post.  IMHO,  Tygon tubing in this service should be inspected on a regular basis and replaced at the first sign of degradation.

The replacement wasn't as difficult as I originally thought.  I removed the pilot's seat ,  glare shield, baggage compartment side panel, and all the lower side panels.    I joined the hoses together with a short piece of 1/2" wood dowel and a couple of screws.   Pulled the old hose from the front and feed the new hose in from the rear.   Snaking  the new hose in place was the easiest part of the job.  I spent more time removing and installing panels.    If I had to do it again,  the pilot's seat and lower side panels would stay in place.  The two tricky spots for snaking the hose in place can be accessed from the baggage area.

Bill

image.jpeg

image.jpeg

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  • 2 weeks later...

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