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Tip: Use of AN fittings with Nylon tubing

T

Ted Radclyffe

Active Member
I am in the process of running the various static and pitot tubes etc in nylon tubing. I was about to use Nylo-seal fittings which are big and bulky behind the instruments when it was suggested that I simply use AN-4D fittings with the 1/4" nylon tube as I would for aluminium tube.

Sounded a good tip but I found that the tubing was very prone to pulling out after flaring as the nylon reverts to its original profile when tightening the filtting.
Tip.....
What I found was that if I flared the tube and whilst still in the flaring tool I gently heated the whole kit and kaboodle with a heat blower (hair dryer is hot enough) then let the tube and tool cool, the flare remained beautifully after the tool was removed.
Another tip...don't forget to put on the sleeve nut first!
 
Fittings

The nylon fittings would have been a better choice. We have them, and no problems with fitting.. A better choice then "adapting" an AN fitting would have been brass with plastic compression ferules. They're cheap. strong for the job, compact and simple to install. Most large harware stores carry them.
T88
RV10
 
pitot fittings

The easiest method to plumb the pitot/static system is with no fittings! :eek:

Just but barbs on the instruments and hook everything together with a handfull of plastic tees and clear plastic hose. The purists hate this but it works beautifully, installs very quickly, and has been working great for years in a bunch of RVs.

Sam Buchanan
 
Sam Buchanan said:
The easiest method to plumb the pitot/static system is with no fittings! :eek:

Just but barbs on the instruments and hook everything together with a handfull of plastic tees and clear plastic hose. The purists hate this but it works beautifully, installs very quickly, and has been working great for years in a bunch of RVs.

Sam Buchanan
Click to expand...

I used some rubber tubing that comes with condensing gas furnaces that I install. It's for draining acidic water & and handles carbon monoxide vapors. Slips right over the pilot/static tubes, and seals airtight. Used it for connections to the aluminum tubing from the wing as well as the plastic tubing.

BTW-- I also like the blue silicone static tubing that comes with the Rapco vacuum pump kit. I'd have run more of that behind the panel instead of the stiffer plastic tubing, had I been aware of it.
 
Sam,

What size and type of tubing is the standard for this approach? I looked at the barbed fittings that fit into the nylon tubing that comes with the kit and they are TINY! The orifice in them just looked a bit too small for my taste. I'm thinking that a bigger tubing would've been the way to go. In the end I used the Nyloseal fittings, but am not really all that happy about all those screwed together failure points.
 
low tech, simple, cheap, can be quickly modified.......and doesn't leak.

from Mr. Adamson
I used some rubber tubing that comes with condensing gas furnaces that I install. It's for draining acidic water & and handles carbon monoxide vapors. Slips right over the pilot/static tubes, and seals airtight. Used it for connections to the aluminum tubing from the wing as well as the plastic tubing.
Click to expand...
Yep, same here (only I used clear "plastic" hose I found in a hardware store). I have found this to be one of the most secure connections you can make. If someone doubts the integrity of this joint, just try to pull one apart! You'll have to cut it apart but that is ok since you only need another short length of hose to hook it back together.

from Mr. Zicree
What size and type of tubing is the standard for this approach? I looked at the barbed fittings that fit into the nylon tubing that comes with the kit and they are TINY! The orifice in them just looked a bit too small for my taste. I'm thinking that a bigger tubing would've been the way to go. In the end I used the Nyloseal fittings, but am not really all that happy about all those screwed together failure points.
Click to expand...

I use barbed fittings from an auto parts store. Many instruments accept 1/8" NPT fittings and if I recall, the barbs I found were for 3/16" hose (might have been 1/4" but you get the idea......this ain't rocket science....). Then you only need some tees with the same size barbs to plumb the whole system. As Adamson stated, a foolproof way to transition to the aluminum tubing is to use a 3" length of tubing that fits over the aluminum tubing and inside/outside whatever tubing you are using behind the panel (you can use a couple of different sizes to nest the transition if necessary...sounds a lot more complicated than it really is).

Grab some fittings, got to Home Depot, stand in front of their assortment of hoses......and figure it out. :D

The beauty of this system is that it is low tech, simple, cheap, can be quickly modified.......and doesn't leak.

Sam Buchanan
 
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Leaks

Sam .. the plastic tubing pushed over barbs can leak over time when expose to high temperature (like the desert... :) ..) Ask sailplane pilots in the Mojave..

My sailplane uses these fitting everywhere and the neat trick is to push (roll?) a small O-ring over the tubing before installation. After the end of the tubing is pushed onto the barbs, the O-ring can be rolled back so it falls into the narrow portion of one of the barbs. This will apply a nice sealing pressure around the tube. Cheap and easy...

gil in Tucson....
 
Sam .. the plastic tubing pushed over barbs can leak over time when expose to high temperature (like the desert... ..) Ask sailplane pilots in the Mojave..
Click to expand...

I'll have to defer to your experience in the desert since my history is limited to the hot, muggy South. :)

My sailplane uses these fitting everywhere and the neat trick is to push (roll?) a small O-ring over the tubing before installation. After the end of the tubing is pushed onto the barbs, the O-ring can be rolled back so it falls into the narrow portion of one of the barbs. This will apply a nice sealing pressure around the tube. Cheap and easy...
Click to expand...

Sounds like a reasonable belt and suspenders approach. I haven't had the need to use the o-ring but it seems like a clever solution if the need arises.

I have found some tubing to be more pliable than others. The "softer" tubing seems to conform and to and grip the barbs very aggressively, so much so that it is nearly impossible to pull the tubing off the barb. A little prowling in the aviation department of various hardware stores or your local auto parts emporium will turn up tubing that is suitable for our uses.

Sam Buchanan
 
Use of AN fittings on nylon tubing (continued)

Thank you all for the advice on perhaps not being too quick to use AN fittings with plastic tubing..
I now have some barb fittings installed. I did however use some bulkhead AN fittings to bring the tube from the wings through the side of the cockpit area.
I suppose I still feel that if one uses AN fittings with Nylon then heating the fllaring tool and nylon tubing will hold the flare after the tool is removed..

Anyway I took on board the discussion and modified my ideas.....that's what it's all about!
 
I'm going to try these with the nylon tubing. If I can find them in 1/8" NPT. Ace Hardware will have something :D

Male-Connector-2GUR9_AS01.JPG
 
Quick connect/disconnects

I've been using these from the home supply stores

059561d5.jpg


Here I'm connecting 1/4 aluminum to 1/4 plastic for my AOA pitot.
Easily disconnected too.
 
Actual Tygon brand tubing seems to work the best. Very pliable, doesnt stiffen up like the vinyls. Seems to last forever.. Probably have to order it.

10 years of RV9 use without a leak, and many more years in various sailplanes before that.

As long as you dont think youre building a 737, this will work great.:D:D


Sam Buchanan said:
I'll have to defer to your experience in the desert since my history is limited to the hot, muggy South. :)



Sounds like a reasonable belt and suspenders approach. I haven't had the need to use the o-ring but it seems like a clever solution if the need arises.

I have found some tubing to be more pliable than others. The "softer" tubing seems to conform and to and grip the barbs very aggressively, so much so that it is nearly impossible to pull the tubing off the barb. A little prowling in the aviation department of various hardware stores or your local auto parts emporium will turn up tubing that is suitable for our uses.

Sam Buchanan
Click to expand...
 
route?

Soft plastic it is! Any suggestion as to how to route them (1 a/s and 1 AOA) from the left wing root through he spar? I hope to go side of the cockpit left wall, just not sure of the best way past the spar...
Thanks, Jim
 
Av8torTom said:
I've been using these from the home supply stores

059561d5.jpg


Here I'm connecting 1/4 aluminum to 1/4 plastic for my AOA pitot.
Easily disconnected too.
Click to expand...

I've seen a number of these installed, and they usually leak.

My observation for what works well:
The quick release fittings that stein sells
Nylo-Seal tube and fittings (do not try to push this onto a 'T', use only with nylo fittings).
Barb fittings and good hose like stratoflex 193 or similar
 
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Walt said:
I've seen a number of these installed, and they usually leak.

My observation for what works well:
The quick release fittings that stein sells
Nylo-Seal tube and fittings (do not try to push this onto a 'T', use only with nylo fittings).
Barb fittings and good hose like stratoflex 193 or similar
Click to expand...

I've used the ones like Stein sells for stuff at work, they work great, and are SO easy to deal with. Just make sure you get a good cut (Stein sells cutters, but a SHARP knife works good, too).
 
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