Online Community of Zenith Builders and Flyers
It's time to replace my old rubber fuel lines and I'm considering switching to aluminum or braided steel/Teflon so I don't have to do this again in five years. Has anyone studied the merits of each hose type? Intuitively, the braided steel with Teflon seems like it would be the most crash/fire resistant, but at ten times the cost of the other options I'd like to see some data to back that up. I did a bit of searching online but couldn't find anything... I don't really know where to begin looking for that sort of thing though.
I'm currently leaning towards aluminum because it's good enough for certified aircraft and relatively cheap and easy to work with, but I'm open to being persuaded in a different direction.
Oh, and in case anyone is installing rubber hoses, I saw someone recommend lubricating the fittings before installing the hose (I think it was Jan E. in one of the Homebuilt Help tips of the week on YouTube). I've had to destroy some fittings to remove my rubber hoses, so that's probably good advice!
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).
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?
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.
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! :)
I think I'll give it a try. Thanks for the detailed answer, John. That's what I like about this site!
I agree with John, great product. Another source is Summitracing.com.
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
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
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.
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.