More Bad Flares on Fuel Lines Found, What's up with this?

[az_gila]

Originally Posted by Ironflight

Well Gil, I don't usually disagree with you, but at Oshkosh last year, i talked with a couple of different manufacturers of Teflon hoses, and both said that they need to be replaced at intervals "set by the airframe manufacturer". Neither one indicated that their lifetime is indefinite.

Paul

CYA? While the airframe manufacturer requirements always rules for STC or certified applications, the FAA and hose manufacturers have published otherwise. Note that inspections are required...

Teflon™ is the DuPont trade name for tetrafluoroethylene
resin. It has a broad operating temperature range
(−65 °F to +450 °F). It is compatible with nearly every
substance or agent used. It offers little resistance to
flow; sticky, viscous materials will not adhere to it. It
has less volumetric expansion than rubber, and the shelf
and service life is practically limitless. Teflon™ hose
is flexible and designed to meet the requirements of
higher operating temperatures and pressures in present
aircraft systems. Generally, it may be used in the same
manner as rubber hose. Teflon™ hose is processed and
extruded into tube shape to a desired size. It is covered
with stainless steel wire, which is braided over the
tube for strength and protection. Teflon™ hose is unaffected
by any known fuel, petroleum, or synthetic base
oils, alcohol, coolants, or solvents commonly used in
aircraft. Teflon™ hose has the distinct advantages of
a practically unlimited storage time, greater operating
temperature range, and broad usage (hydraulic, fuel,
oil, coolant, water, alcohol, and pneumatic systems).

Above from FAA document http://www.faa.gov/library/manuals/a...83-30_Ch07.pdf

From www.amtonline.com

The Air Force requires all rubber hose assemblies be replaced after 10 years from date of assembly manufacture, and PTFE hose assemblies shall be replaced “on-condition.”

An Aeroquip document -

The effect of heat on Teflon hose is completely different from that of rubber hose. Unlike the more common organic rubber compounds, Teflon or "Tetrafluorethylene", as it is more properly known, does not harden when being used at elevated temperatures (-SJCF to +400°F), but stays uniform in texture and consistency.

From an Eaton hose document - http://vargaair.com/admin/wp-content...n_fittings.pdf

Service and shelf life of Eaton’s
Aeroquip Brand Teflon hoses
are unlimited for all practical
purposes. However, experience
has shown that service life on
impulsing applications may eventually
be limited by fatigue in the
wire reinforcement. Maximum
service life on such applications
is best determined by the operator,
based on his experience.

It was not my personal random comment....

I belief in our relatively easy RV applications they have an essentially unlimited life if inspected carefully every annual.

[Ironflight]

I knew I'd pry more research out of you with that comment Gil - thanks!

The only thing I'd continue to press is...how do you determine the condition of the interior of a Teflon hose to ddetermine if it is in need of replacement? You can flex it and see if it is getting crispy, but can't tell what's going on inside. And no one will give a ballpark figure. It's just something to consider.

Don't get me wrong - Teflon hases are FAR superior to rubber hoses in every way. But I don't think thre is enough evidence yet on ultimate life.

[az_gila]

Originally Posted by Ironflight

I knew I'd pry more research out of you with that comment Gil - thanks!

The only thing I'd continue to press is...how do you determine the condition of the interior of a Teflon hose to ddetermine if it is in need of replacement? You can flex it and see if it is getting crispy, but can't tell what's going on inside. And no one will give a ballpark figure. It's just something to consider.

Don't get me wrong - Teflon hases are FAR superior to rubber hoses in every way. But I don't think thre is enough evidence yet on ultimate life.

There is an inspection procedure document, but it is a newer AS document that costs $$$ and is not on-line as far as I could find...

Don't know about a "ballpark" figure, but the FAA words are -

...service life is practically limitless...

Sounds good enough for me in our typical applications when used as a replacement for a rubber hose...

[JonJay]

Originally Posted by az_gila

There is an inspection procedure document, but it is a newer AS document that costs $$$ and is not on-line as far as I could find...

Don't know about a "ballpark" figure, but the FAA words are -

...service life is practically limitless...

Sounds good enough for me in our typical applications when used as a replacement for a rubber hose...

Thread is drifting a bit but this topic is important.
I hope we can get our hands on that document at some point. The worry I have is that unlike rubber hoses, that had a measurable service life and showed signs before failure, how do you know if you have a teflon hose going bad? I had a teflon hose failure on the Bucker. It was a simple drain line from the bottom of the fuel tank in the cockpit area, no heat, no pressure... The inside of the hose about mid way just collapsed after about 10 years, 130 hours or so. You could not see it at all from the outside. I will assume it was defective from the start but who knows.

[TS Flightlines]

Teflon, like other hose liners, will take a set over a period of time, due to heat and fluid cycles. Like Aeroquip 303 style hose, once teflon has been in service, dont take it off and flex it, or try to straighten it out to inspect it. Even though we dont have the temperatures that the hoses were intended for, you can still damage the liner or cause cracks that may not be able to see. If you need to remove them, (and you are going to reinstall them), support them so you can maintain the bends that they have.
Running oil temps to 250* is not a problem for teflon, as this is well within its intended temperature range.
Having seen some teflon hoses that were subjected to heat (exhaust), and abrasion, the liners are very durable. BUT, they will not take abuse, such as non-firesleeved appications laying on hi-heat exhaust. The stainless braid will fail, and the liner will be directly affected by the heat.
If you plan your hose routings correctly, your hoses will last the lifetime of your airframe. This has been proven in commercial and military applications,
Tom

[FlyingArcher]

Tom,

Please check your PM
Thanks

[az_gila]

Originally Posted by JonJay

Thread is drifting a bit but this topic is important.
I hope we can get our hands on that document at some point. The worry I have is that unlike rubber hoses, that had a measurable service life and showed signs before failure, how do you know if you have a teflon hose going bad? I had a teflon hose failure on the Bucker. It was a simple drain line from the bottom of the fuel tank in the cockpit area, no heat, no pressure... The inside of the hose about mid way just collapsed after about 10 years, 130 hours or so. You could not see it at all from the outside. I will assume it was defective from the start but who knows.

Several of the documents previously listed stated that the smooth bore Teflon hoses can be kinked in handling. Perhaps this is what happened to yours?

My previous post mentioned "long life" but in the context of a rubber hose replacement - ie, under the same operating conditions. Higher stresses, such as heat, certainly would reduce hose life spans.

[az_gila]

Originally Posted by JonJay

Thread is drifting a bit but this topic is important.
I hope we can get our hands on that document at some point. .....

I think this is the document

SAE AIR Report ARP 1658, "Hose Assemblies, Installed, Visual Inspection Guide"

http://standards.sae.org/arp1658b/

[terrye]

Originally Posted by az_gila

I think this is the document

SAE AIR Report ARP 1658, "Hose Assemblies, Installed, Visual Inspection Guide"

http://standards.sae.org/arp1658b/

Unfortunately, many of the old AN, MS, NAS documents which were public domain, are being obsoleted and SAE (Society of Automotive Engineers) has been recreating them as AS, ARP and various other standards. These are not public domain, and so we as users have to pay a substantial amount to purchase them. Fortunately, most of the AN, MS and NAS parts are still recognized and manufactured, but for standards such as the teflon hose inspection standard, we're probably have to pay $$

[Don]

I started plumbing this afternoon and because of the comments here I probably proceeded with more than an average amount of care and caution. I mike'd each flare to be sure it wasn't over done and I inspected each flare carefully under bright lights and with magnification. I rejected my first 4 flares and then proceeded to produce acceptable flares pretty consistently...if only I could consistently get the sleeve on in the right direction or not cut a tube a half an inch short. More practice.

I try to be careful and pay attention to detail in everything I do on the 9, but sometimes, I simply don't know what it is I don't know. Flaring tubing and especially not over-torquing the fittings were a couple of the things I didn't know well enough. This thread alone was sufficient to justify my $25 contribution to Doug. Thanks one and all.