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  #1  
Old 10-01-2020, 10:20 AM
rocketbob's Avatar
rocketbob rocketbob is offline
 
Join Date: Jun 2006
Location: 8I3
Posts: 3,643
Default Push fitting leaks

Over the last several years I've been using push lock fittings for pitot/static connections. On a few occasions I've had these fittings leak and last night I examined a leaky tube and fitting closely under magnification to determine why. These fittings use a small conical washer with tabs to embed into the plastic tubing to retain them. During insertion the washer can scratch the tubing which causes an imperfect seal against the o-ring. Normally when used in higher pressure applications the oring seals work fine because they get compressed. The simple solution is to use a tiny amount DC4 silicone grease on the tube end during insertion which helps prevent the tube from being scratched and helps with the oring seal.
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  #2  
Old 10-01-2020, 11:22 AM
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Raymo Raymo is offline
 
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Default

Great tip. Thanks, RB.
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  #3  
Old 10-01-2020, 11:44 AM
Ralph Inkster Ralph Inkster is offline
 
Join Date: Feb 2008
Location: Calgary, Alberta
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Default

Have had great results with SafeAir slip on fittings sold by Cleaveland Tools (formerly carried by Avery). These are the ones with the dark grey plastic lock ring (easy to disconnect). I have used the green lock ring fittings as used (I think) in Dynon & Garmin plumbing kits but don't like them because they physically clamp to the tube and wont release easily, I consider them single use connections.
Only issues I've encountered involved where wrong type plastic tubing was used in the installation or poor end cuts (not 90 deg. cuts) caused leaks.
Our local Avionics shop wish they could use these fittings on all planes as its an extreme rare event to find a leak, compared to the crappy 'certified' fittings they have to deal with on 'certified' jobs.
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  #4  
Old 10-01-2020, 01:41 PM
scsmith scsmith is offline
 
Join Date: Jan 2008
Location: Ashland, OR
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Default

I had such chronic leakage problems with those push fittings that I finally abandoned them and plumbed the whole airplane with old-style nylo seal fittings. Those work great. The key for the nylo seal fittings is to use the little insert ferrule inside the end of the tube so the compression fitting has something substantial to squeeze down on.

I finally got a tight static system that would pass a 91.411.

With RocketBob's suggestion, I might consider going back to the push fittings on a fresh build, with all new tubing. Once a push fitting has been opened/closed a couple of times, I think the chances of having the tubing get scored becomes pretty high, and once it is, well, you just have to replace that piece of tubing.
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  #5  
Old 10-01-2020, 01:59 PM
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scard scard is offline
 
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I fully jumped ship a few years ago and went way back to tygon and barbed fittings.
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  #6  
Old 10-01-2020, 02:05 PM
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The push-in fittings work well under pressure applications - they don't work worth a flip for vacuum line like MAP sensor lines.
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  #7  
Old 10-01-2020, 02:07 PM
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Walt Walt is offline
 
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Location: Dallas/Ft Worth, TX
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Quote:
Originally Posted by scsmith View Post
I had such chronic leakage problems with those push fittings that I finally abandoned them and plumbed the whole airplane with old-style nylo seal fittings. Those work great. The key for the nylo seal fittings is to use the little insert ferrule inside the end of the tube so the compression fitting has something substantial to squeeze down on.

I finally got a tight static system that would pass a 91.411.
What Steve said, Nylo is always my first choice, and trust me I've fixed plenty of static leaks.
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  #8  
Old 10-01-2020, 06:02 PM
DaveWelch DaveWelch is offline
 
Join Date: Mar 2005
Location: Huntsville, AL
Posts: 447
Default No problems

Hmmm...just for a bit of “balance” in the thread, I’ll chime in and offer that I’ve had no problems with the push fittings that Vans changed to a while back. Meaning the ones with the green release ring. They solved my leak problems on both the brakes and pitot-static systems (fingers crossed now that you guys may have jinxed me &#128521.
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