Air vacuum pump troubleshooting

FORANE

FORANE

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FORANE
We just went through annual condition inspection on our O-320 equipped RV-9A. We flew the RV-9A 60 miles or so back to our home airport. The next day we departed and on climbout lost suction. This motor only has 120 SMOH.

How to troubleshoot?
Is there a means of testing the lines to the AI and DG to confirm they are not the cause?
Is there a means of testing an air pump? Disconnect line to pump and look for debris?
 
If it's a dry pump, first thing is to look at the plastic couple that goes between it and the drive case. The most common mode of failure is a stuck blade which leads to instant destruction of the drive (purposely set up as 'the weak link' in the system to sheer before something more serious breaks). If it is broke, you need a new pump.
 
Henning said:
If it's a dry pump, first thing is to look at the plastic couple that goes between it and the drive case. The most common mode of failure is a stuck blade which leads to instant destruction of the drive (purposely set up as 'the weak link' in the system to sheer before something more serious breaks). If it is broke, you need a new pump.
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Thanks Henning

I had heard of this. I'm not in the same state as the plane right now. Is it possible to spot a sheared couple without removing the pump? i.e., could I expect to be able to ask my wife to look at it and be able to tell without removal of the pump?
 
FORANE said:
Thanks Henning

I had heard of this. I'm not in the same state as the plane right now. Is it possible to spot a sheared couple without removing the pump? i.e., could I expect to be able to ask my wife to look at it and be able to tell without removal of the pump?
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The ones I recall you could look in some ports in the mounting flange where the drive lug resides.
 
You can see the coupler at the drive end of the pump. Slowly turn the propeller by hand and you can see if the pump is turning or not. If not the shaft has sheared which, as Henning pointed out, it is designed to do.
 
Failed pump just as predicted; Henning nailed it.
111mdmv.jpg
 
Was it an old pump on a new engine? Or had the previous pump failed and spit busted bits into the hose and system, which the new pump then sucked in and began to destroy itself? The vacuum inside the instruments is enough to suck back broken carbon bits like that when a pump abruptly fails. Something to consider with this one.

If that pump is old, the drive might just have aged. Most of those manufacturers recommend a replacement drive coupling after six years. Heat and oil take their toll on the plastic.

Dan
 
Dan Thomas said:
Was it an old pump on a new engine? Or had the previous pump failed and spit busted bits into the hose and system, which the new pump then sucked in and began to destroy itself? The vacuum inside the instruments is enough to suck back broken carbon bits like that when a pump abruptly fails. Something to consider with this one.

If that pump is old, the drive might just have aged. Most of those manufacturers recommend a replacement drive coupling after six years. Heat and oil take their toll on the plastic.

Dan
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I have never seen a set of vanes in one of the dry pumps outlast the coupler. Typically a vane wears out and jams and the couple pops. Used to be able to get replacement vanes and a coupler and just redo the pump every 400hrs and stay ahead of the destruction. I prefer wet pumps though, lot more reliable.
 
That was definitely an older pump as all the new ones have cooling fins on the case.

The newer Tempest pumps have enclosed the area around the drive coupler to prevent solvents and oils from getting on plastic and helping lead to premature failure.
 
CMTowner said:
That was definitely an older pump as all the new ones have cooling fins on the case.

The newer Tempest pumps have enclosed the area around the drive coupler to prevent solvents and oils from getting on plastic and helping lead to premature failure.
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The oil gets past the seal in the pump's drive and contaminates the graphite vanes and makes them sticky, destroying the pump. The nylon drive can tolerate oil a lot better than the pump's innards.

Dan
 
Might want to take a look at your oil system to see if there's any sign that any metal escaped into the engine. It shouldn't have, but it would be really expensive if it did and you continued to run your nice, new engine that way.
 
Ron Levy said:
Might want to take a look at your oil system to see if there's any sign that any metal escaped into the engine. It shouldn't have, but it would be really expensive if it did and you continued to run your nice, new engine that way.
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Care to explain how oil gets from a dry pump into the engine? In my thirty years wrenching I've never seen that. :confused:
 
Dan Thomas said:
The oil gets past the seal in the pump's drive and contaminates the graphite vanes and makes them sticky, destroying the pump. The nylon drive can tolerate oil a lot better than the pump's innards.

Dan
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Oil can get in anywhere, and should it get into where the carbon vanes are, it can turn that carbon dust into goo. I'm not saying it is common, but I have seen it. I've replaced many of the oil seals at the pump drive too.
 
Ron Levy said:
Might want to take a look at your oil system to see if there's any sign that any metal escaped into the engine. It shouldn't have, but it would be really expensive if it did and you continued to run your nice, new engine that way.
Click to expand...

How would the shearing of a vacuum pump drive coupler introduce metal to the engine :dunno:
 
Indeed it was an older pump on a roughly 100 hr SMOH motor. I looked at the pump closely and the date code is from 1997.

Pump has been replaced. Filter and hose to filter were replaced but no signs of debris or dust sucked back toward them. The filter did look dirty on the outside though.

I started a new thread about what to do with the old air pump - rebuild or no.
 
CMTowner said:
Oil can get in anywhere, and should it get into where the carbon vanes are, it can turn that carbon dust into goo. I'm not saying it is common, but I have seen it. I've replaced many of the oil seals at the pump drive too.
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There was a small amount of oil at the air pump flange including a very small amount of what appeared to be sludge like oil mixed with carbon dust at the bottom of the drive mechanism mount.
Should I have changed a seal also? Is it hard to do?
 
FORANE said:
There was a small amount of oil at the air pump flange including a very small amount of what appeared to be sludge like oil mixed with carbon dust at the bottom of the drive mechanism mount.
Should I have changed a seal also? Is it hard to do?
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The pump's mounting studs and nuts also retain the drive assembly. It has to come off, the gear and shaft drop out, and the seal can be picked out and replaced. BUT: that shaft gets a groove worn in it and sometimes a new seal won't help much. And the new seal should get a little sealant on its outer circumference when it's installed, too, since I've seen them leak right there.

The broken carbon gets get sucked into the hose to the instruments and the instruments themselves, not into the filter and its hose. That hose from the pump to the vacuum regulator should be checked for debris.

Dan
 
Dan Thomas said:
...The broken carbon gets get sucked into the hose to the instruments and the instruments themselves, not into the filter and its hose. That hose from the pump to the vacuum regulator should be checked for debris.

Dan
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I'm not following this Dan, since the pump is the lowest pressure point in the system how would debris get "sucked" into the instruments? Same for the regulator, isn't it simply a bleed valve?
 
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