Does Avgas eat any kind of o-ring?

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Chris M
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Does Avgas eat any kind of o-ring?

#1 Post by Chris M » Thu Jul 16, 2015 6:42 am

My very tiny club uses a manual hand crank on a 500 gal tank to refill our two airplanes. For some reason the pump seems to eat seals at an alarming rate. One of our members thinks it's due to side loads on the handle (which is entirely possible, it's a good reach to get on top of the tank so you're working from an odd angle). I'm not aware of any rubber o-ring material that would be incompatible with 100LL but thought I would see if anyone here had experienced something like this.

In the future we may go to a battery powered 12V pump with a solar panel and battery tender. It would definitely be a nice upgrade.
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ahramin
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Re: Does Avgas eat any kind of o-ring?

#2 Post by ahramin » Thu Jul 16, 2015 7:40 am

Yes absolutely avgas will eat o-rings. Before using any o-ring I let it sit in avgas overnight and then check it to make sure it isn't flaking. I'm sure someone else here can tell you what types of rubber are ok and what types aren't.
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Re: Does Avgas eat any kind of o-ring?

#3 Post by Meecka » Thu Jul 16, 2015 10:02 am

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Re: Does Avgas eat any kind of o-ring?

#4 Post by iflyforpie » Thu Jul 16, 2015 10:27 am

In aviation, o-rings are specific to the application. Fuel and hydraulic fluids use different specs. Even 5606 and Skydrol o-rings are incompatible.

Incorrect installation wil also result in problems (twisted, not lubricated, no backup rings, wrong size, damaged groove, wrong shape or thickness, rough handling, expired shelf life).
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CID
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Re: Does Avgas eat any kind of o-ring?

#5 Post by CID » Thu Jul 16, 2015 2:09 pm

ahramin wrote:Yes absolutely avgas will eat o-rings. Before using any o-ring I let it sit in avgas overnight and then check it to make sure it isn't flaking. I'm sure someone else here can tell you what types of rubber are ok and what types aren't.
Wow.
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Re: Does Avgas eat any kind of o-ring?

#6 Post by Heliian » Fri Jul 17, 2015 6:35 am

It may not be the type of material used but the application. The seals are lubricated by the medium (fuel in this case), which will evaporate quickly and leave the seals dry, next time you crank, the dry seal gets damaged and so on until it leaks. A proper pump will help you in this case as it sounds like you may be using one designed for oil or more slick products.
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Re: Does Avgas eat any kind of o-ring?

#7 Post by PilotDAR » Sun Jul 19, 2015 5:11 am

Heliian makes a valid point, are you sure that an O ring is the proper type of seal? My hand pump has a leather packing, which is compressed around the piston rod by tightening a gland nut. It does not mind operating dry a few strokes, until the fuel comes up to wet it.

There are certainly right and wrong O rings for gasoline, though generally, any O ring intended for gasoline these days, should tolerate Avgas okay. A Senior Cessna Engineer told me that when Cessna changed their line fuel from 100/130 to 100LL, all the new planes weeped fuel. They had to replace O rings throughout the fuel system, and sourced them from automotive suppliers, as the automotive gasoline O rings could tolerate the higher aromatics now in the 100LL. This was also my experience, when we started using Mogas, we just replaced the original O rings with new, and problem solved...
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Re: Does Avgas eat any kind of o-ring?

#8 Post by niss » Tue Jul 21, 2015 4:24 am

PilotDAR wrote:It does not mind operating dry a few strokes, until the fuel comes up to wet it.
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Re: Does Avgas eat any kind of o-ring?

#9 Post by GyvAir » Tue Jul 21, 2015 5:19 am

That's NOT what she said...
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Re: Does Avgas eat any kind of o-ring?

#10 Post by hoserjoe » Sun Nov 01, 2015 6:34 pm

Dupont Viton fluoropolymer elastomer o-rings resist fuel and acids better than any other types, in my experience. Believe it or not, there are companies that specialize in o-rings, with excellent customer service, and Google will help you.
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Re: Does Avgas eat any kind of o-ring?

#11 Post by Strega » Sun Nov 01, 2015 8:26 pm

I think you need to hire an AME that will rebuild the fuel pump for you,, otherwise, it will not be safe.

They might charge you a lot, but in the end, you will know that it was done correctly.
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Re: Does Avgas eat any kind of o-ring?

#12 Post by DonutHole » Sun Nov 01, 2015 9:21 pm

What you really need is a real engineer to design a pump that doesn't use orings.
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