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Scooter
Joined: 10 Jan 2006
Posts: 155
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 Posted: Sat Aug 11, 2007 12:46 pm Post subject: Compressor |
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Always a fun topic. So the issue is the compressor is a bit lethargic. Maybe making about 40atm and taking some time to do it. After landing and using the brakes a bit I might only have 35 when i put it away.
After running there's enough residual pressure to blow the snot out but maybe not as much as before. If I add external air the pop-off operates up around 50atm.
I removed the cowl and checked hose couplings with the engine running and didn't detect any leaks (I would guess that it would be noticeable with your hand clamped over the fitting?). Haven't yet attempted to charge the pump-to-snot section and check for leaks.
I'm thinking this will probably require a compressor rebuild and am assuming it will most likely be the rings on the piston. Any chance I can pull the cylinder and replace these rings or should I pull the entire assembly? Anyone know roughly what a rebuild costs? Note that I've read the previous posts on removing the compressor, etc. great advice and I'm not looking forward to it.
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Bill Tally
Joined: 11 Jul 2007
Posts: 20
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| Posted: Sat Aug 11, 2007 3:09 pm Post subject: Re: Compressor |
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I claim to be no expert on this subject (there are many on this forum much more knowledgeable than I am), but I went through exactly the same thing over the course of a couple of months. We first noticed low or no air production and little or no snot. After ruling out leaks, I cleaned the output valve by soaking in solvent. That worked for a while but output soon fell off again. That cycle was repeated a two or three times with the same result.
I was convinced that the compressor was bad and actually bought a rebuilt compessor. I quickily learned that the job of replacing the compressor is a real beast (to be very polite) and requires biblical patience and specialized tools. I spent the better part of a day trying to figure out how how to access several nuts that you can barely see, much less reach. That convinced me to try the output valve one more time. This time, I completely disassembled it, cleaned it and polished all the moving parts. I lubed everything well and put it back in. To my amazement, it worked and has worked perfectly ever since. That may not fix your problem, but it's much easier than fooling with the compressor.
You are getting some output, so you can rule out a sheared drive shaft. The problem has to be either a leak, a problem with the output valve, or an internal pump problem (internal valves, rings, etc.).
As you said, leaks should be ruled out first, especially around the banjo fittings and the coiled tube going to the moisture collector. You can pressurize the system with shop air by disconnecting the tube where it goes into the moisture collector. Wrapping a few turns of black electrical tape around the nozzle of an ordinary shop blow gun allowed us to get a good seal on the tube and to pressurize the system. If there are no leaks, then go to the output valve. Take it apart and make sure it's completely clean. Note how it goes back together; it is possible to put the valve in upside down. Use new aluminum crush washers everywhere, including the banjo fitting. Some have also suggested squirting turbine oil or some simliar lube into the pump inlet (behind the filter) to free up the internal valves.
The moral to the story is that pump replacement is a difficult task best avoided if at all possible. If the compessor needs overhaul, it has to come off. There is no other practical way to get it apart without creating a huge mess. (Don't be tempted by those nuts on the top.)
If you need crush washers, parts, or a pump, Jill at Carl Hays Enterprises can help you.
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dsavarese(at)elmore.rr.co
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| Posted: Sun Aug 12, 2007 5:52 am Post subject: Compressor |
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Pull the output check valve assembly from the compressor. Clean it and
replace the crush washers with new crush washers. Make sure the spring in
the check valve is not broken and the little piston and its spring moves
freely with light pressure. It is quite common to have the output check
valve banjo fittings leak under higher pressure due to the cap loosening and
the crush washers not completely sealing.
I would also pull the snot bottle off the airplane and thoroughly clean and
flush it out. This too can cause the system not to properly charge to the
full pressure relief valve setting (ie: the pop-off valve). While you're at
it, you might as well remove the one and only air filter directly below the
pop-off valve and clean/replace it. IF you can disassemble it, Doug Sapp
stocks the internal screens for it.
Dennis
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Scooter
Joined: 10 Jan 2006
Posts: 155
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| Posted: Mon Aug 13, 2007 6:52 am Post subject: Re: Compressor |
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I appreciate all the input. I'm attaching a diagram of the compressor for those who are following but don't have one at hand.
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viperdoc(at)mindspring.co
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| Posted: Mon Aug 13, 2007 11:05 am Post subject: Compressor |
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And we always thought the USSR were inferior and simple minded! It has been
awhile since I looked at the diagram but danged if it is not complicated!
Anybody converted the gear on the YAK to hydraulics? It would put a stop to
all this carboned bypass valves and clogged snot valves but bring on its'
set of headaches. At least they would be self lubricating though.
Doc
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mark.bitterlich(at)navy.m
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| Posted: Mon Aug 13, 2007 3:09 pm Post subject: Compressor |
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And would weigh more.
Mark
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