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Soft Tubing To Hard Line??

S

szicree

Well Known Member
I've got the standard issue plastic tubing for my static and instrument plumbing, but aluminum tubing for my wing pitot plumbing. What is the consensus for joining these two types of tubing?
 
20031222_silicone_joint.jpg

The clamps are apparently overkill and unnecessary, but whatever.

http://www.aircraftspruce.com/catalog/appages/siliconehose.php
 
I used an AN fitting on the AL tube and a plastic fitting with ferrules to the plastic tube. Both went to NPT, one male and one female, joined together to form an adapter.

Roberta
 
Yeah, thats probably how certfied airplanes would do it. I think those plastic ferrals are prone to leaking... after 25 years or so. You should be good for awhile.
 
I used an AN fitting on the AL tube and a plastic fitting with ferrules to the plastic tube. Both went to NPT, one male and one female, joined together to form an adapter.
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Yeah, thats probably how certfied airplanes would do it. I think those plastic ferrals are prone to leaking... after 25 years or so. You should be good for awhile.
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The fuel tank vents in our old Warrior only had a short length of rubber hose connecting the aluminum tube coming out of the tank to the alluminum tube in the wing. No clamps, no AN fittin's, no nuthin' but a rubber hose.

That's the way it came from the factory.

Sam Buchanan (RV-6 with the pitot system plumbed with nylon and aluminum tubing joined with short lengths of non-clamped flexible tubing.....seven years and still tight...)
 
But the vent doesn't have to hold any kind of pressure, thus it's a vent. Pressure lines are a different story. I do agree however that flexible hose is plenty for the Pitot, since it doesn't exactly run high pressure.
 
Im very curious and hope someone can tell me this. Any idea what type of pressure we are talking about in the pitot line at 200mph? 1, 2, 3 psi? I'm just looking for a close estimate.

-Jeff
 
But the vent doesn't have to hold any kind of pressure, thus it's a vent. Pressure lines are a different story. I do agree however that flexible hose is plenty for the Pitot, since it doesn't exactly run high pressure.
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I thought this thread was about pitot plumbing, not pressure hoses. :)

Try pulling one of the "rubber hose couplings" apart and you might start entertaining questions of just how much pressure it could potentially hold. The only way to get one of these connections apart is to cut it.

Sam Buchanan
http://thervjournal.com
 
RV_7A said:
Im very curious and hope someone can tell me this. Any idea what type of pressure we are talking about in the pitot line at 200mph? 1, 2, 3 psi? I'm just looking for a close estimate.
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200 mph CAS = 0.7 psi pitot pressure, roughly speaking.
 
Thanks Kevin...
Now its pretty clear to see what type connections could be used safely between the two.
 
Flare it

I just flared the plastic tubing like you would the aluminum and used standard AN fittings. After reading this thread, I'll probably cut that off and use a bit of silicon tubing. That should save a couple of grams. I can have cheese on my next burger!
 
Bob Collins said:
fabulous connections
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fabulous except for the price, and the fact that you can't get the tubing out through the snap bushing without cutting the connector off and thus shortening it...just my 2 cents, KISS and use silicone sleeving.
 
Dan,

Any reason you went with this particular type of tubing? I'm planning on a similar setup but would prefer to use something a little thinner walled (passing through a grommet).
 
szicree said:
Any reason you went with this particular type of tubing? I'm planning on a similar setup but would prefer to use something a little thinner walled (passing through a grommet).
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I went with the silicone hose I used because printed on the outside of it is "for instrument use only" (if I'm recalling correctly). I used the stuff that is intended for air instrument tubing.

I don't think it's too critical, but definitely keep maintenance in mind. If you use a life-limited material, be sure to inspect it on a regular basis and be sure you can access it to replace it...and that ideally it won't require cutting any existing tubing.
 
Direct to pitot mast?

Bob Collins said:
Check out the fabulous connections SafeAir1 sells for joining the aluminum to the plastic.

AoA_Pitot_Conn_01.jpg
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I'm probably struggling unnecessarily with this. I've just read several dozen forum posts but can't quite find the answer. I have the SafeAir1 pitot air kit and an Evans Aviation pitot tube (unheated). I'm wondering why I cannot buy (I think) an AN8153D union which has 3/8" thread both sides and screw one side directly into the pitot mast and the other into the platic tube coupling doohicky shown above. Do I need to have a short length of aluminium tubing, and if so why? Surely it is just a whole load of additional connections that could/might failure. Why add potential failure points? Am I missing something here? Other than having the correct connectors at the moment!! :)
 
Unheated Pitot? I see no reason why you can't run the soft tubing directly to the fitting screwed in as you purpose. When I tried that with my Heated pitot on the workbench, it melted the tubing right off (boy did THAT stink up the workshop!), but unless I'm missing somehting, your proposal sure sounds easy to me.

Paul
 
dan said:
...and the fact that you can't get the tubing out through the snap bushing without cutting the connector off and thus shortening it...
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If you are talking about the plastic tubing, sure you can, you just press in on the little black ring sticking out/up, this releases the pressure on the tube and you can remove it from the fitting.
 
For those trying to figure out how to connect the aluminum pitot line to a plastic line, I used a plastic fitting I had left over from an ice maker install kit. They come in quarter inch size and since they're designed for the relatively high pressure in you water supply, they are perfect for pitot lines. Inexpesive, light and readily available. Below is a photo.


 
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PSI in a pitot static system

Kevin Horton said:
200 mph CAS = 0.7 psi pitot pressure, roughly speaking.
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Please

What psi does flexible rubber or vinyl tubing have to endure for a pitot static system? 1psi? Is fuel line rated at 60 psi sufficient? Is flexibility a problem? I need to connect a 3/16 aluminum tube with flexible hose.

Thanks
 
The static side of the system sees negligible pressure under normal operation, but would see more significant pressures during the static system check. If the pitot static test set takes the static side to 18,000 ft and the aircraft is really at sea level, there will be 7.3 psi pressure difference between the ambient pressure outside the tubing, and the lower pressure inside.

The pitot side would see roughly 1 psi at 200 kt CAS (230 mph) and 1.5 psi at 250 kt CAS (288 mph). It would see similar pressures to the static system during the static system test.

60 psi rating seems more than sufficient.

It needs to be flexible enough so you can get a good seal using whatever method you use.
 
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Static system testing in non-pressurized airplanes is a delta P of 1,000 ft. Not much.

Pitot testing it left to the aircraft manufacturer, but usually something like a delta P of 100 kts for unpressurized airplanes.
 
I used short bits of tygon line aka vinyl tube to connect to aluminium tube. I went around twice with safety wire pull tight and twist. Low cost low weight very effective clamp.
 
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