What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Do Air / Oil separators get clogged?

Kooshball

Well Known Member
Just curious as my RV4 is the fist plane that I have owned that has an oil / air separator on it...do they typically get clogged or need any kind of regular inspection / cleaning?

Thx
 
The antisplat air/oil separator with the one way valve connection to the exhaust have been known to get clogged and needs regular inspection. I believe they call for a 50 hour inspection but I could be wrong on the number of hours.
 
Just curious as my RV4 is the fist plane that I have owned that has an oil / air separator on it...do they typically get clogged or need any kind of regular inspection / cleaning?

Thx

No. Everything running through it is pretty clean and drains away.
 
The antisplat air/oil separator with the one way valve connection to the exhaust have been known to get clogged and needs regular inspection. I believe they call for a 50 hour inspection but I could be wrong on the number of hours.

To clarify - it's the check valve at the exhaust pipe connection that needs to be checked and cleaned, at least on each annual. The heat from the exhaust can cause coking of the oil mist and plug that valve. I'm not aware of any issues with the separator itself, which operates in a normal-FWF-temp environment.
 
To clarify - it's the check valve at the exhaust pipe connection that needs to be checked and cleaned, at least on each annual. The heat from the exhaust can cause coking of the oil mist and plug that valve. I'm not aware of any issues with the separator itself, which operates in a normal-FWF-temp environment.

To clarify, the blockage forms in the steel tube between the check valve and the exhaust header. The photo below is an example of buildup. Left alone, the ring of greasy coke will eventually close the passage.

There are considerable differences between installations, which has resulted in very different service experiences. For example, an Anti-Splat tap on an RV-10 tailpipe seems to suffer a very rapid coke buildup. At the far end of the spectrum, a tap mounted a few inches from a cylinder exhaust port has never been cleaned. The tube in the photo below is mounted on a single downpipe and gets cleaned at 50 hr oil change intervals, with the photographed buildup being typical. It's also an opportunity to inspect the one-way check valve. I found a failed NAPA 2-29000 at the most recent inspection; it would pass air both ways. That's not a critical failure, and interestingly, there was less buildup in the tube.

If your separator system includes an exhaust tap, be sure it also incorporates a safety pop-off valve...another check valve like the one on the exhaust tap, arranged so if the tap clogs, the safety valve vents crankcase pressure. Again, see below.

To the OP's question, there are so many different styles of separator in service that I think it is impossible to absolutely say they are impervious to blockage of some kind. I think you just check whatever you have at annual, by whatever method is appropriate.

Article here:

https://www.danhorton.net/Articles/Separator-or-Condenser.pdf
.
 

Attachments

  • Breather Buildup.jpg
    Breather Buildup.jpg
    86.1 KB · Views: 280
  • Evacuator Safety Valve.jpg
    Evacuator Safety Valve.jpg
    23 KB · Views: 242
To Dan's point, location of the valve (and model of the engine/exhaust) does seem to make a difference. I mounted my valve pretty far towards the end of the pipe and my valve does not choke off between annuals, but has about the same as Dan's picture would show, and I'm averaging about 150 hours between annuals.
 

Attachments

  • IMG_0801.jpg
    IMG_0801.jpg
    290.4 KB · Views: 229
Mine (in my Jodel) is a home brew version of the ACS one. I don't plumb it into the exhaust. The vapor goes out a vent tube and the liquid collects and I drain it out after flight. Periodically I clean it out and it is full of sticky goop. That goop likely is much more liquid when hot gases are going through the separator. I have the whistle hole in the tube from the crankcase vent to the separator and a small vent hole in the top of the separator in case something freezes.

But to answer your question, there is some really gnarly stuff in there, so left to its own devices I would not be surprised if it could clog up, even if you were draining it to the exhaust or somewhere. I understand some people drain it to the sump but that seems like a bad idea to me. The guy who wrote the sky ranch manual compared that to running a tube from your butt back to your mouth!
 
But to answer your question, there is some really gnarly stuff in there, so left to its own devices I would not be surprised if it could clog up, even if you were draining it to the exhaust or somewhere. I understand some people drain it to the sump but that seems like a bad idea to me. The guy who wrote the sky ranch manual compared that to running a tube from your butt back to your mouth!

Every single component that reaches the separator originally came from within your crankcase. Knarly or not, it is no different in chemical composition than everything else floating around the crankcase. Not sure why someone would be afraid to put it back from where it came.

My V8 BMW has two air oil separators, which drain back to the sump. I pulled them at 100K miles when replacing the rubber tubing. Separators were pristine and required no cleaning. There is no scheduled maintenance to clean or replace them.

Can't imagine BMW got this wrong. Though I suppose it is possible that a bad design could cause problems with debris collection and clogging.

Larry
 
Last edited:
Thx folks. I will have to look a bit closer at the details of which one I have the next time the cowling is off for an oil change.

In my case I have an inverted oil system and I wonder what happens to the oil / separator during inverted and vertical flight.
 
Back
Top