Pros and cons with teflon fuel-lines?

Hi you engine guru's out there.

I bought the IO-360 Lyc from Vans about two years ago and a couple of days ago, it was time to install the FT-60 FF sensor (the"red cube").
As on my other -7, the plan was to install the sensor on the fuel-line beetween the engine driven fuelpump and the fuel injection servo.

However, the airplane-shop who installed the same type of sensor on my first -7 couldn't do it this time since the fuel-line Vans provided in their FF-kit now is made of teflon.
The fuel-lines on my first -7 where made of the usual rubber-type and they had no problem working with them back in 2007.

I now have a couple of options.

1) Send the fuel-line and the sensor to someone in the US who can work with teflon fuel-hoses.

2) Have the airplane-shop make new fuel-hoses made of rubber and have them install the FF-sensor on that one.

Since option 1 is both time-consuming and expensive, I would rather go for option 2, but then I'd have rubber fuel-lines.

I don't mind having rubber fuel-lines at all, but is the any good reason I should keep the teflon-lines?
Any advantages beside that those will live "forever"?
I don't mind changing the rubber-fuel lines every 10 years...
(I have read somewhere that rubber-lines schould be replaced at that interval)

So: before making any decitions, it'd be interesting to hear what you engine-guru's are saying about teflon vs rubber?
(Mel; are you there?? )

ao.frog said:

I don't mind having rubber fuel-lines at all, but is the any good reason I should keep the Teflon-lines?
Any advantages beside that those will live "forever"?
I don't mind changing the rubber-fuel lines every 10 years...
(I have read somewhere that rubber-lines should be replaced at that interval)

So: before making any decisions, it'd be interesting to hear what you engine-guru's are saying about Teflon vs rubber?
(Mel; are you there?? )

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Standard fluid lines do typically last for 10 years or more if not disturbed. However, I believe the recommend replacement period is 5 years. And that includes shelf life.
I ran my first standard lines over 10 years, but I don't recommend that. When I removed them they were very stiff. Once they get stiff, they begin to deteriorate.
Personally, I recommend the Teflon lines.

Thanks alot for chiming in Mel!

Ok, I'll keep the teflon-lines on my 2nd -7 and on my 2st -7, I'll plan to replace my rubber-lines with teflon as well when they are due for replacement.

I'll also update my maintenace-log to say 5 instead of 10 years for rubber fuel-line replacement.
I didn't think of including shelf-life to those 5 years, so I guess I've some fuel-lines to replace this summer...

Teflon is virtually bulletproof chemically speaking. I have used it almost universally from agressive industrial solvets to 50% hydrochloric acid and everything in between.

I would have no hesitation in using teflon hoses (for 100LL and mogas with or without ethanol) and I bet they have a very long service life (although I don't KNOW what it would be).

Seeing as I have the local hydraulics shop make mine up for next to nothing I could replace them evry year if I wanted to..No point though.

Frank

At Oshkosh last year, I asked the two major suppliers of aviation grade Teflon-hose what the lifetime should be (when they would recommend replacement). Both of them said the exact same thing - "That will be determined by the aircraft manufacturer". (Kind of a funny way to respond at an "Experimental" aircraft show, but let's not start that argument...)

The bottom line was that neither would give me any number at all regarding service life, and both suggested that it was not infinite. I'm sure their response was (at least partially) lawyer-driven.

Paul

We use either Teflon or stainless lines exclusively at my work. Teflon is used without service life restriction to carry 100% IPA, Acetone, 40% HF acid, 40% hydrogen peroxide, and HCl gas just to name a few. The only degradation I have ever seen is on the furnace gas exhaust lines which carry away process tube acid exhaust from a 1000 deg C furnace. After 5 or more years of that kind of heat they tend to loose flexibility and can crack when moved.

I don't think there is anything to worry about for our applications.

I can't think of a single downside to teflon lines.

What have I missed?

Is there an easy way to determine which one is Teflon and which is rubber hose? I have used what VANs supplied (less than four years ago). How do I know if it is Teflon vs. rubber since it is covered.

Recently I was at the International Motorsports Industry Show here in Indy and I had a look at some of the latest racing hoses and fittings. Goodridge makes a new convoluted teflon hose with black Kevlar jacket that in -6 size it is pressure rated at over 1000psi and has a burst rating of 3900psi. Incredibly light. Google "Goodridge 710".

Alf-

sent you a PM.
Tom

To check wether you have teflon or not, you have to cut off one off the steel band and look at the connection underneath.
I don't know what to look for but maybe someone else does?

At least that was what I was told when I was at the local airplane-shop.

Maybe someone else know an easier way to check that?
Can it be found on the hose-label for example?

The Goodridge hose is great!
Tom

Alf--You dont have to cut a perfectly good hose to identify it.
Are the hose ends crimped, or red & blue resuables? The red & blue hose ends on steel braided hose will be for 701 style hose which has a 'rubber' liner.
Crimped on hose ends on stainless braid will be teflon. IN MOST CASES!
Some of us can crimp aluminum hose ends to teflon hose---yep custom stuff. Put some pics on here---
Tom

Minimum bending radius

Teflon is the best. About the only negative that I have heard of is that it is easier to "kink" a teflon hose because of its minimum bending radius being higher than rubber hoses. I am just careful to avoid real tight bends when installing, that's all.

Kyle Boatright said:

I can't think of a single downside to teflon lines.

What have I missed?

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The FAA recommends an hydraulic pressure test at a maximum test interval of 6 years for all aircraft hoses, including Teflon hoses. Basic aviation safety principles dictate that you do not want to use a product in service until it fails (certainly not fuel hoses). Teflon hoses "may" have an indefinite life if one considers that they are "on condition" subject to proper periodic pressure testing and normal ongoing hose inspections.

However the periodic testing represents a problem for Teflon hoses in that the "set" of any bend in the hose needs to be maintained during the removal of the hose, during the hydraulic pressure testing, and during the reinstallation. From a practical point of view that is not easy to do. Certainly the hose will need to be fully restrained to hold any bend during the pressure testing as the test pressure will want to straighten the hose. Straightening a Teflon hose that has a long term service bend is guaranteed to cause microscopic cracking of the Teflon leading to subsequent failure.

Another "problem" with Teflon hose is that the specified installed bend radius needs to be significantly greater than for standard 601/AE701 rubber hose. The former requires a minimum radius of 4.0" compared to the 2.5" of the latter (for -6 hose). Consequently the design of the routing of Teflon hoses requires more consideration and planning and the hose lengths generally need to be more precise.

Then there is the problem of ensuring that the Teflon hose is of proper aviation quality, meaning that it must be fabricated from "conductive" Teflon. If you obtain a Teflon hose from your local friendly hydraulic hose shop chances are they will not even stock conductive Teflon hose (or know about it). So if YOU don't know exactly what you want you could get something entirely unsafe for the application.

I have used Teflon hoses in my FWF set-up because I believe they offer some advantages...but as with most "higher" technology products the quality control in terms of fabrication, installation, and periodic testing becomes more critical.

Looks like the Goodridge 710 hose has the conductivity issue covered. It has a conductive lining.

(link to pdf catalog here)

The aramid outer braid is nice. It may not be as big a deal in aviation usage- notably since hoses are usually firesleeved- but in automotive applications I've seen more than a few cases of stainless braid on poorly secured hoses act as a hacksaw. Pretty good temperature range for an all-synthetic product.

Thanks for the tip, rocketbob!

I was kind of amazed with the Goodridge hose when the rep showing it to me at the show wrapped it around his finger, and it didn't kink.

Conductive teflon..Hmm,

Well considering that the non conductive type was pumping highly flammable solvents over miles of pipes for years on end in our buildings I highly doubt its a hazard in 3 foot of pipe where any charge can leak away to both ends

Remember the tube is surrounded by steek braiding that is grounded at both ends.

Frank

Captain Avgas said:

Another "problem" with Teflon hose is that the specified installed bend radius needs to be significantly greater than for standard 601/AE701 rubber hose. The former requires a minimum radius of 4.0" compared to the 2.5" of the latter (for -6 hose). Consequently the design of the routing of Teflon hoses requires more consideration and planning and the hose lengths generally need to be more precise.

Click to expand...

Lars said:

Looks like the Goodridge 710 hose has the conductivity issue covered. It has a conductive lining.

(link to pdf catalog here)

Click to expand...

Am I reading that doc right that the Goodridge 710 teflon hose needs less than a 1.0" bend radius for the same size hose being discussed?

Seems like quite an improvement!

The danger of non-conductive teflon fuel hoses

frankh said:

Conductive teflon..Hmm,

Well considering that the non conductive type was pumping highly flammable solvents over miles of pipes for years on end in our buildings I highly doubt its a hazard in 3 foot of pipe where any charge can leak away to both ends

Remember the tube is surrounded by steek braiding that is grounded at both ends.

Frank

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All certificated Teflon fuel hoses are now fabricated from conductive Teflon. The danger for builders in the Expererimental Category using non-conductive Teflon fuel hoses in their aircraft is very real.

When teflon hose was first used on aircraft it developed pin-hole leaks. The non-conductive Teflon used was capable of developing a static charge so great that it could arc to the grounded steel braid causing a small hole in the Teflon.

Now, Military Specification MIL-H-25579E requires that hoses (through -8) be capable of conducting a direct current equal to or greater than 6 microamperes with a test potential of 1,000 volts dc between the hose inner liner and one end fitting. This prevents the build-up of static charge and arc pin hole leaks to the wire braid.

But don't take my word for it (or Frank's). Here's a short article from the respected Sacramento Sky Ranch on the subject that makes for easy reading:

http://www.sacskyranch.com/statichose.htm

And here's a photo showing what conductive aviation grade Teflon looks like. Normal Teflon is white but the conductive aviation grade Teflon is typically grey because it contains Carbon to promote conductivity.

rocketbob said:

Recently I was at the International Motorsports Industry Show here in Indy and I had a look at some of the latest racing hoses and fittings. Goodridge makes a new convoluted teflon hose with black Kevlar jacket that in -6 size it is pressure rated at over 1000psi and has a burst rating of 3900psi. Incredibly light. Google "Goodridge 710".

Click to expand...

Personally, I think Experimental builders would be wise to stick to aviation grade hoses (and fittings) for their fuel lines. Choosing Milspec hoses means they will not have to do a whole lot of research on the subject and can be comfortable that their hoses will provide the best possible performance in the unique aviation environment.

There is no more critical area in terms of safety on your aircraft than the fuel supply system. It's certainly not an area where you want to be trying to save a few dollars or be too "experimental".

Look at Vans. Typically most of the third party products they supply on their kits are low quality non-aviation grade components. But when it comes to FWF fittings and hoses it's all aviation grade milspec. That Scrooge McVan won't compromise on these items probably tells you something.

Yep---not all teflon hose is the same. BUT----most aerospace hose manufacturers have industrial divisions. Aeroquip, Stratoflex (Parker) Titeflex, Teleflex have have excellent quaility industrial hose. Their conductive hose is made to the same mil specs as the aerospace hose, perhaps without the traceibility, and extra documentation. ( as told to me by a Titeflex engineer).
Where problems for aircraft arises is when non-conductive, imposter hose is used. Generally speaking, all hose will handle the 80-100 psi of oil systems, and certainly the 25-30 psi of fuel systems. ( any one seen hose clamps on oil and fuel hoses? How about push on barbed stems?) It's the liner makeup that poses the problems. Always use a conductive teflon liner, .030 or .040.

Bob mentioned Goodridge. They have been a supplier to all forms of motorsports for years. Excellent quality. Alittle hard to get here in the US, but good stuff.
Tom

http://www.kevineldredge.com/Networ...tries/2010/9/17_AN_fitting,_Expensive!!!.html

Nice aviation-grade AN stuff here. One can argue easily that the fitting should have been steel, the hose better supported, yada yada yada. The truth is that if an item has a trail of paperwork it doesn't necessarily make it better. In this case I would argue that a far lighter and more flexible hose would have at least delayed significantly the onset of a failure in the fitting.

I agree Bob-- Aeroquip 701 hose used here. "rubber" (neoprene, nitril) liner. The Aluminum AN fitting has been used for years in aviation, but no fitting would survive that type of damage. Even a teflon hose, whether aerospace AS grade or not, would still have damage. I think the point is to use good acceptable materials. The benefits of teflon hose has been well documented on VAF before. We can all make suggestions, but the last decision goes to the builder, and what he or she wants to use.

OOPS--i didnt see the last pic on Bob's post. Yeah steel, or stainless adapter 'might' have prevented it. Good idea to check them at conditional inspections, and when you are changing hoses.

ao.frog said:

I now have a couple of options.

1) Send the fuel-line and the sensor to someone in the US who can work with teflon fuel-hoses.

2) Have the airplane-shop make new fuel-hoses made of rubber and have them install the FF-sensor on that one.

Click to expand...

Many mount between servo and spider..... don't know if you are open to that, but certainly a third option many find to work quite well or arguably better.

Auto Priced Conductive Teflon Fuel Hose

Where can you buy -4 and -6 automotive priced Teflon Fuel Hose that is conductive and that has fittings you can add yourself? I'd like to make some fuel lines to add the Red Cube. I could buy the hoses pre-made for a couple hundred bucks, but I'm not sure of length and I'd like to make them myself so I can play with length.

Plus, can I cut one of Van's hoses to shorten it and add a new fitting to it?

thanks

Steve--there are several places you can get some reusable -4 hose ends for teflon hose. Phenix Industries, Earls, Russell, etc all make very good hose ends. Getting a conductive hose to match up is alittle harder, as most of those use a non conductive hose. Phenix has some conductive, and the matching reusable fittings.
Tom