when I built my XL, I replaced the "stock" rubber fuel lines with braided stainless steel coated lines that I fabricated.

After reading the Service Letter that Zenair published last February (02/05/2018 Rev. 0)

under item #3 "Fuel Lines in Airframe" I started to wonder if there is a replacement interval for these fuel lines? (I'm in the middle of my Annual Condition inspection)

Obviously the stainless steel mesh precludes a visual inspection of the enclosed rubber fuel lines-but I have not seen any evidence of degradation (no black flecks in the sumps or gascolator)

Calendar-wise these lines are 4 years old

time wise they have about 120 hours on them

I only run AVGAS through them, no MOGAS

Your thoughts?

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I plumbed my 750 with PTFE-lined braided stainless except for a Parker rubber fuel line (all-rubber with a firesleeve) between my firewall and my engine and Jabiru USA recommended a 5 year replacement interval.  The PTFE-lined braided stainless does not require replacement.

John

N750A

Thanks for the info.

Next question is; how do I determine if mine is PTFE lined or is all stainless braided lines PTFE by default?

Not all braided stainless is PTFE lined.  Since you fabricated the lines, perhaps can look up the source and see what you used, or, if you have some of the scrap line (I never throw anything away, Ha!), look at the lining - PTFE will appear as a relatively hard plastic liner - either white or gray-black.  (The gray or black lining is carbon impregnated for conductivity and is really what should be used to avoid static build-up.)

John

OK  so playing the devil's advocate here and assume that it is NOT PTFE and IS braided and covered, do you feel that there is still a finite replacement interval of say 5 years?

or is it a "upon signs of deterioration" like flecks of rubber in the gascolator?

Any scrape line left over you can look at? Invoice with part number you can look up the specs? If they are rubber under S/S versus PTFE under S/S the fittings to fabricate the hoses are different as well. Can you recall or have any left over fittings to help ID type line?

after talking to John I'm confident that they are rubber (Not PFTE) under stainless.

So now the question that remains is do I replace per calendar or on condition (IE: presence or lack thereof of rubber debris in the fuel system)

If I have to refab the lines I will-of course. But I don't want to refab and replace perfectly good lines if there is no evidence of deterioration. (Similar to TBO being a recommendation)

The extra safe approach with rubber hoses is five years. That is the official recommendation from most of the hose manufacturers and also from the FAA mainteniance folks. In the real world rubber flex lines usually go ten years without any problems at all. On some poorly maintained planes I have seen flex lines that looked to be many decades old and were still not leaking but they certainly were stiff, inflexible and covered with surface cracks. It is not good to let them age too much or you could have a failure at an inconvenient time.

One down side (other than being expensive) to the stainless wrapped teflon hoses is there is, to my knowledge, no easy way to fabricate them yourself. They require special tools and procedures to build and must be made up in specialized shops. If you want to upgrade to the teflon hoses, the best way is to send them your current hoses and they will duplicate the hoses to match. That way you don't have to worry about measuring wrong. When the new hoses are built the shop sends you back your old hoses and your new hoses, same size hose, same length, same style fittings on them. This advice is if you are having new hoses made up at a certified aircraft hose shop.

Since you have an experimental airplane you can also use stainless wrapped teflon hoses from automotive supply houses. There are many stock hoses sold by places like Jegs and Summit Racing and others. They are marketed as extra strong and durable hose for automotive brakes, fuel lines, etc and are available in a lot of sizes, lengths and fitting types. One cannot use these hoses legally in a certified plane but can legally use them in a homebuilt. You, as the builder, determine what is a suitable part for your plane. Don't buy cheap Chinese junk from some discount parts place, buy top quality stuff from a top tier auto parts supplyer and you will be fine.

For any hoses in your plane that do not have an automotive teflon and stainless hose of the correct size and fittings, your only option that I know of is to have them built at a specialty shop as outlined in the second paragraph above.

The stainless wrap protects the hose from physical damage but the rubber hose inside it does degrade slowly over time. That is why the Teflon hoses wrapped with stainless braid are so nice - they have no known age limit and have the metal braid protecting them. They are expensive but well worth it. If you plan on keeping the plane a long time I would recommend upgrading to stainless wrapped teflon hoses. If you just want to keep on keeping on, I would start thinking about replacing them sometime after five years but no later than ten years.

The above is personal opinion based on fifty years of messing with airplanes but is not an expert opinion or the word of a certified mechanic. Make your own decision but since you asked for advice, I thought I would give you some. 

No, your advice and that of John and David pretty much confirms what I suspected.

Can you use the same AN fittings on the PFTE lines? or will I need to buy all new fittings to make the switch?

This will be a "bad" year for maintenance between ADS-B out and the Slick mag SB so I will probably push out replacing the fuel lines til my next annual (Dec '19) I have not seen any evidence of rubber degradation thus far and December 2019 will make the lines 6 years old

Can you use the same AN fittings on the PFTE lines? or will I need to buy all new fittings to make the switch?

Totally different fittings - the braided stainless/rubber lines simply push onto the fitting and are secured by a nut to the fitting.  The braided stainless/PTFE lines have an "olive" that is pushed down over the hose (under the stainless braid) and then are secured with a nut to the fitting.  I can't say enough good things about Earl's fittings sold at ANplumbing.com.  There, you can buy the specific fittings for their hose and be assured no leaks. I've never had a problem with them in 6+ years and 560+ hours.  The lines run through the cockpit area and I've never even smelled a whiff of gas fumes, much less had a leak!  Pricey stuff but it'll last a lifetime or two.  :>)

John

Just make sure if you are talking to the sales rep at Summit Racing that you do not ever use the word "airplane".  They will put a notation in their computer and ban you from buying anything from them.  At least that is what I have been told. 

I just ordered their catalog, thanks for the advice.

Lucky for me there is a local speedshop that I've used before.

I'm hoping I can reused the AN fittings I already have

RSS

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