I recently learned about this. See http://www.nastyz28.com/forum/showt...leed+fuel+vapor.

Both Earl's and Aeroquip admit the problem with no guaranteed solution. Earl's recommends teflon hose. See http://www.earls.co.uk/earls/car/3_...form-o-flex.pdf.

Aeroquip says NONE of their hoses, and that includes teflon, can withstand fuel injection recirculated gas. See http://www.aeroquip.com/media/perfo...MC001-E-p54.pdf.

The parts tech at my Chevy dealer says GM fuel hose also has to be replaced every 4-5 yrs.

I guess I'll have to use all metal fuel lines on my current fuel injection project unless somebody has experience with hose that doesn't leak gas vapor odor. Any ideas?

is this only related to FE systems? must have something to do with the higher fuel pressures, otherwise this sounds like an expensive exercise, I like the braided lines, hate the price and building them, so I not wanting to redo the lines every 5 years, it take my finders that long to heal.

"I guess I'll have to use all metal fuel lines on my current fuel injection project unless somebody has experience with hose that doesn't leak gas vapor odor. Any ideas?"

You really should run metal lines everywhere except where the line has to flex. That is usually just a short piece from the tank to where the hard line is attached to the car and from the car over to the engine.

I've never noticed Teflon hose have the vapor problems and Aeroquip doesn't say that it does it the tech bulletin you linked to:

"A Caution about Fuel Injection
All hose listed in this catalog is suitable for use with
leaded and unleaded fuels. However, caution must
be used in fuel injection systems that recirculate fuel.
This causes fuel to oxidize which can attack the hose
inner tube. To increase service life, keep the time of
exposure to the oxidized fuel to a minimum. Drain
hose line or flush with original fuel or other
suitable material."

Nothing in that statement says that Teflon hose can't handle use for fuel injection systems that recirculate fuel. They just made a lawyer approved general statement acknowledging that these systems cause shortened service life in the inner tube of hoses.
Teflon hose has been used in aircraft for better than 50 years with fuel, hydraulic, oxygen systems and more with no signs of tube deterioration. In aircraft (especially military) the dates of manufacture of hoses are required to be on both ends of hose Assemblies for maintenance purposes. Different types of hose material have different storage and service lives, dictated by a number of Technical Standards Orders (TSOs). The acceptable shelf life for rubber hose is 32 Quarters (8 years) but none is listed for Teflon. As long as Teflon hose assemblies continue to pass visual and hydrostatic testing the service life is determined by the user.

One reason I can see why Aeroquip was more cautious with giving Teflon an endorsement for fuel system use is that the automotive side is a small fraction of their business and they don't wan't to contradict their aviation policies where as earls is only concerned with automotive use.

IMHO..The sky is not falling, TEFLON hose is the right choice for a fuel system. Non-Teflon based hoses do have problems in this area but if you' want Eaton (Areoquip) to come out and say in writing that their Teflon hoses will last forever without inspection and maintenance for ANY application you're in for a long wait!


Age Limitations and Aircraft Hose Life
Introduction
There is come concern within the industry about the misuse of shelf-life and service life. Storage conditions and the environment in which the product is used is more important in determining the useful life than calendar time. Often audits and documentation practices only include shelf life and disregard storage conditions.

In many instances, maintenance manuals include a service life requirement for hoses but have no service inspection or condition replacement criteria. Such policies are wasteful in that perfectly good products are scraped; and such policies are dangerous as products that have been degraded because of harsh storage conditions or operating environment are kept in service.

Service life is installation dependent. For example, we see rubber hose that has been on the aircraft for over 20 years, yet the same rubber hose exposed to high heat next to an exhaust stack may have a service life of several weeks (or until bent). It is our experience that a rubber hose carrying 100 low lead avgas ages faster than the same hose carrying engine oil. What is the service life of a hose? As one aerospace hose manufacturer states: "Only the user can establish this period."



Shelf Life

Reference AS 1933 revision A. (replaces MIL-STD-1523) for rubber age limitation. Generally, 32 quarters (8 years) --at acceptance by ultimate user/customer.

AS 1933 may not mean that a hose that is beyond 32 quarters cannot be installed. For example, the customer could purchase (accept) the hose before 32 quarters and then subject the hose to shelf storage until such time as the customer is ready to install the hose. Shelf storage is measured from acceptance. The Navy, in NAVAIR 01-1A-20 could put the hose into storage for an additional 5 years (MIL-HDBK-695). Do not confuse Shelf Life with Shelf Storage.

Service Life

Service life depends upon service conditions. The hose manufacture is often unaware of service conditions, so the best they can do is offer general guidelines. The airframe/engine manufacturer or maintenance entity is in the best position to establish Service Life as they are the most knowledgeable as to the service conditions.

To quote from Eaton (Aeroquip):

The actual service life of a given hose assembly, in a given application, is dependent on many variable factors. These variable factors may include, but are not limited to, operating pressure, pressure surges, flexing, operating temperatures (both fluid and ambient), installed bend radius, cleaning solutions, ozone and assembly routing. Due to the variety of operating conditions and applications, the user, through their own analysis, testing and/or review of maintenance records and data, is ultimately responsible for making the final selection, of or decisions about replacement hose assemblies and assuring that all performance, safety and warning requirements of the application are met.

Eaton (Aeroquip) for example, has published general criteria to help you establish Service Life criteria. They have separated the hose application into 3 general categories and suggested a Service Life for each category. These categories are:

1. Normal Duty Hoses

Typically, these are hose assemblies in less demanding applications, such as in-body, in-wing or other applications not normally exposed to the environment, cleaning fluids, continuous temperature extremes, heavy pressure pulsation, etc., and having infrequent maintenance actions associated with their installation. Recommended Maintenance Approach: On Condition

2. Moderate or Heavy Duty Hoses

Typically, these are hoses exposed to more frequent maintenance activity or major system removal, or hoses occasionally exposed to environmental conditions (e.g., upper wheel well hoses, APU hoses) Recommended Maintenance Approach: Either On-Condition or based on user data and maintenance records.

3. Demanding or Severe Duty Hoses

Typically, these are hoses continuously or routinely exposed to environmental, cleaning, or other harsh operating variables
such as landing gear brake hoses, EDP hoses, etc., and associated with major systems requiring regular removal, repair or overhaul. Recommended Maintenance Approach: Strongly consider replacement at time of major system overhaul.

--end Eaton Quote--