Replies to This Discussion

Permalink Reply by Matt Pope on January 26, 2022 at 12:26pm

Yeah, there are other types of hose (including rubber) that is reinforced with a stainless steel braid, but I wouldn't consider using those.

PTFE is amazing - I used to work in a chemistry lab and we used PTFE equipment to work with the most corrosive chemicals because it just doesn't react, even at high temperatures.

I've found that there are different grades of PTFE/steel-braided lines used in the auto-racing/hot rod industry, and the more expensive products are significantly lighter and more flexible than the cheaper ones (and only the more expensive ones are made with conductive PTFE to prevent microscopic leaks from forming due to static electricity discharging through the liner).

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Permalink Reply by Matt Pope on January 26, 2022 at 12:37pm

Hi Pat, when I google "fuel injection hose" I find several different types of hose marketed as fuel injection hose - is there one type in particular you like?

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Permalink Reply by Patrick Hoyt on January 27, 2022 at 2:03pm

The hose I used is labeled "Dayco AIS Fuel Injection Hose SAE 30R9".  I believe it came with my engine as part of the FWF package, although it's possible that I purchased it later (I do recall purchasing another quantity of hose at one point during the rebuild).  Made in USA.  I've been happy with the results. 

Interesting discussion regarding PTFE hoses.  Back when I originally built my airplane, PTFE wasn't in the vocabulary (or, at least it was not known to the community in which I was active at that time).  Knowing about it now, I may take a second look at it on my upcoming next project.

That being said, I think the bar is set pretty high to match aluminum tubing in the "hard to inspect" areas, and fuel injection hose everywhere else. 

I'd be interested in hearing about fellow builders decisions regarding going with PTFE versus going with Aluminum in the "hard to inspect" locations.

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Permalink Reply by John Austin on January 27, 2022 at 2:33pm

Patrick,

Stainless braided PTFE hose is nothing new - it's been around for decades and is especially used in auto racing engines, aviation, and even rocket engines!  The stainless steel braid makes it practically indestructible and the PTFE liner is impervious to almost all chemicals and fuels, and it is considered "permanent" when used as fuel lines, while at the same time being flexible so it's not prone to fatigue cracking as can occur with aluminum hard lines.  Because of it's flexibility, I made one continuous run for each tank - no connections in the run for possible leaks - from my bulkhead fitting where the wing joins to the plane to the fuel valve on my console - this involved multiple bends and turns and the only line I can think of that could otherwise do that in one piece is rubber - which isn't permanent for sure.  Parts of those runs were threaded through "impossible to inspect" areas such as inside the upright supports behind the seats on each side of the fuselage.  I sheathed it in corrugated plastic loom just to be sure it didn't rattle or fret against the aluminum support:

As I've said, over 10 years and I've never smelled so much as a whiff of gas fumes and certainly no leaks.  Try it, you'll like it!  :)

John

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Permalink Reply by Patrick Hoyt on January 27, 2022 at 2:39pm

I think I'll give it a try.  Thanks for the detailed answer, John.  That's what I like about this site!

- Pat

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Permalink Reply by Glenn Davis on January 29, 2022 at 8:22am

I agree with John, great product. Another source is Summitracing.com.

Glenn

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Permalink Reply by James Neirinck on January 30, 2022 at 2:07pm

As part of my build I used 3/8" aluminum 3003 versatube.  Easy to use (flare, bend and route) due to it being a softer more flexible aluminum tube but still a permanent solution and good for higher pressure fuel injection systems which I have and required a return line.  It was lighter and more cost effective even with all the AN fittings.  Firewall forward I used Earl's Vapor Guard 3/8" hose covered with fireshield.   Since you are looking to change out existing hose I'm not sure it would be that easy to convert to aluminum lines (although the 3003 Versatube is easy to bend and route around), so I do like John's approach using premium PTFE hose and fittings as it will likely be easier to do and the end result will be outstanding. Good luck.  Cheers, Jim

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Permalink Reply by Matt Pope on January 30, 2022 at 5:34pm

Hi Jim - thanks for your take. I looked at the routing again and there are some pretty inaccessible corners, so I think you guys are right that it will be quite difficult to replace with aluminum (even versatube), so now I'm making a list of all the fittings and lengths I'll need for PTFE. Cheers

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Permalink Reply by Perry Delano on January 31, 2022 at 10:12am

Hi Matt,

Provided you have a good 37 degree flaring tool, a good bender and some extra tube,  I don't see an issue with installing or replacing aluminum lines. under the seat and where the flapperon control rods go (no fuel lines in there) are the only moderately inaccessible areas.  I have redone some of the trickiest sections in my 701 a couple of times to improve the design or fix a crimped line because I was not paying attention tightening a bulkhead fitting.

I think all material will have its pros and cons.

Perry

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Permalink Reply by Matt Pope on February 1, 2022 at 7:37pm

Hi Perry,

My installation is a bit unusual, with a header tank behind the passenger seat. There are also two storage compartments built into the seat backs, and I have to work around those... but as I type this, it occurs to me that it might be much easier if I drill out the rivets holding the storage boxes in place, install the fuel lines, and then re-install the boxes - duh. Thanks for prompting that brainwave! Haha

I had changed my mind back to steel braided PTFE, but the kind I settled on (Earl's UltraPro) isn't available anywhere in Canada right now, and if I want it shipped from the US it will arrive in four months. (If I change my shipping address to anywhere in the Lower 48 though, it can arrive in two days.) I've spent way too much time researching this, but now I'm reconsidering aluminum yet again.

Cheers,

Matt

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