Are all fuel hoses the same?

Automotive fuel hose. How much do you know?

Something you may expect to be a straight forward and even boring is an area where a small mistake has a large impact. Performance and reliability is compromised when a poor selection is made. Everyone’s favourite topics will get a mention. Fuel choice, operating pressure, temperature, flexibility, durability and cost.

When talking about automotive fuel the standard definition for fuel is unleaded fuel (up to 98 octane) and diesel. By this definition standard fuel hose is not compatible with ethanol blends, bio diesel or menthol. 

The topics we are going to talk about are fuel injection, carburettor, in tank applications, fuel type compatible, fitted hose and hard line.

The correct choice is critical. Incorrect fuel hose will result in premature failure causing burst lines, fuel leaks and or breakdown of the fuel hose causing fuel contamination which will block fuel filters and injectors.

EFI applications typically have operating pressures up to 225psi so the chosen hose must be able to provide an acceptable life span operating at these pressures. Typical burst pressure for this fuel hose is in the area of 400psi. In this application three types of hose are used nitrile, nylon and braided.
Let’s deal with nitrile rubber style first. This is the most common of the three. Typically being constructed of a premium inner layer made from NBR (Nitrile), a reinforcing spiral wrap and an outer cover. The nitrile inner layer does not readily break down when in constant contact with fuel and provides hydrocarbon permeation resistance. The textile spiral weave middle layer adds mechanical strength to withstand the operating pressures. The thicker outer cover is often made from CR (Neoprene) and provides temperature protection, abrasive resistance and reduces construction cost. Having good flexibility this hose is easy to use and allows for versatility of installation. Worm type EFI hose clamps or step less clamps and barb fittings are used for connecting hose to fitting.

Many suppliers have EFI fuel hose that is compatible with all fuel types, gasoline, diesel, bio-diesel, E-85, methanol and ethanol fuels.
For sizing EFI hose the inner diameter isused and expressed in imperial measurements and or mm. 3/8 hose is also called 9.5mm. Getting technical this hose is constructed to SAE30R9 and has an operating temperature range of -30 degrees C to +100 degrees C with burst pressure as high as 4 to 5 timers the operating pressure.
The one big thing to remember is this hose is not for use inside fuel tanks. It is not going to self-destruct but the outer layer will break down over time when in constant contact with fuel blocking fuel filters and injectors.

Nylon tube is the fuel hose of choice by manufacturers. The main reason for this is having the ability to reduce evaporative emissions to very low levels(very low permeability). Additional benefits are the smooth internal surface and the ability to be made to conform to shape. Conforming to shape and nylon quick connects makes installation very quick and easy at the vehicle production stage. Manufacturers love that. The nylon quick connect push on fittings provide fast and secure connections. Having said that as the quick connects age the security of the connection is reduced necessitating replacement.

Nylon is resistance to most fuel types including nitro methane, has an operating pressure of 250psi and burst pressure of up to 1000psi. The operating temperature range of -30 to 120 degrees C  and it is available in rigid and flexible convoluted tube. The convoluted tube is often use in tank for the fuel pump to module connection. This convoluted hose is well suited to in tank use due to its flexibility and resistance to being submersed in fuel. On the downside nylon hose requires special tools to replace the quick connects and is a little more difficult to work with due to the rigid construction. As you can see in the picture nylon hose is a single layer in construction. This simple construction greatly reduces cost.

Braided hose is a little more complex. Available in both nitrile and PTFE inner core with stainless, polyester or nylon braid. The nitrile braided hose has the same properties as EFI hose.
Dash (-) numbers are used to identify the sizes of braided hose. A -6 hose will use a -6 fitting. Not only is the correct dash size required but also the correct fitting type with braided nitrile and PTFE  hose useing unique fittings. Generically called braided hose the real term is 100 series, 200 series and so on. The series number identifies the fittings required and the hose construction. 200 series is the hose guaranteed to be compatible with all modern fuels. Nitrile braided hose is 100 series.

Braided nitrile hose does allow fuel to permeate through. For this reason braided nitrile must only be used on the exterior of vehicle and never inside the cabin. Use this hose and you will have the smell of fuel around the vehicle. No fuel leaks just the smell. Stainless steel brained nitrile hose can be used in submersible applications.
Braided PTFE is light weight and easy to assemble. The achievable bend radius is less compared to the other braided hose and often additional hose fittings are required for neat installation. PTFE is compatible with all fuels and oils. With operating pressure of 1200+psi and burst pressure of 4000+psi for performance applications this is a very good choice. Teflon or PTFE is 200 series hose.

When talking about performance style hose push lock must get a mention. Push lock is a nitrile hose and has all the same properties. The fittings however are very different. They are very simple to install and provide very good service. For reasons I am not aware of some people have a great dislike of push lock style hose and fitting. Claiming failures of the hose and connections. Personally I have not witnessed a failure when the connection is correctly produced and the hose is well maintained.

We have mentioned submersible fuel hose a number of times now so let’s go a little more in depth.
Ordinary fuel hose is only designed to resist fuel contact internally. In a submersible application the exterior of the fuel hose is in constant contact with fuel. There are two distinct players, rubber style including stainless steel brained and nylon.
The rubber style submersible hose is constructed to meet the requirements of SAE 30 R10. This style of in tank hose will have an external flouroelaster tube cover to retard aging, aramid fibre used for the spiral wrap and a nitrile inner. Operating pressure of 250psi and busrt pressure of 500psi make this hose suitable for EFI systems. Flexibility is limited when compared to non-submerible EFI hose.

I have heard claims of nitrile submersible hose bursting. Once again I have never witnessed this and see it as unlikely. It would have to be faulty hose, incorrect clamps or possibly a sharp bend radius causing cavitation or erosion. I have never had the opportunity to examine a burst in tank hose to determine the cause of the failure.
Nylon hose for in tank use has already been covered and is a very good choice for in tank use.

Did you ever think about using the cheaper low pressure hose for return line on your EFI vehicle? Carburettor or return hose is very similar in construction to EFI hose just designed for lower pressure. Typically the operating pressure is <50psi. Being rated to less pressure make cost of production less that the higher pressures hoses.
Size of the fuel hose is the same as EFI and compatibility with the different fuel type is also hose specific. This hose is manufactured to comply with SAE30R7

Seamless aluminium hard line is a cost effective choice for high and low pressure fuel lines. Very clean installation possible with full length seamless line. Hard line maybe more time consuming to install as it requires the use of tube benders and cutters. Fitting wise compression and flare fittings are commonly used. Hard line has exceptional durability being the best of all fuel lines. Burst pressures are similar to other fuel lines being in the range of 780psi. Stainless steel hard line is also an option.

Static discharge should not be overlooked. Fuel hose needs to be able to discharge static build up that occurs due to the fuel flowing within the hose. As fuel flows at high velocity the friction caused by the fluid will generate static electricity. All high quality fuel hose will have a conductive chemical additive to allow the static electricity to discharge safety through the hose to the vehicle body.

That’s plenty of information to enable good decisions when selecting your fuel hose.

Hose or pipe used to transfer fuel from one point in a vehicle to another

A fuel line is a hose or pipe used to transfer fuel from one point in a vehicle to another. The United States Environmental Protection Agency defines a fuel line as "all hoses or tubing designed to contain liquid fuel or fuel vapor. This includes all hoses or tubing for the filler neck, for connections between dual fuel tanks, and for connecting a carbon canister to the fuel tank. This does not include hoses or tubing for routing crankcase vapors to the engine's intake or any other hoses or tubing that are open to the atmosphere."[1]

Materials

[

edit

]

Rubber

[

edit

]

Most vehicles have rubber fuel hoses connecting the fuel pipes on the chassis to the fuel pump or carburetor on the engine. Rubber hoses are flexible and can be cut to length as required, but they have a tendency to perish over time and can rub through if not properly secured.[2]

Plastic

[

edit

]

More modern vehicles may be fitted with fuel lines made of plastic, typically nylon. Plastic fuel lines do not perish and are lighter than metal tubing, but they melt at lower temperatures and cannot be repaired as easily.[3]

Steel

[

edit

]

Many FF or FR vehicles with fuel tanks at the rear are fitted with rigid steel fuel pipes that run the length of the chassis from the tank to the engine bay. Steel pipes are cheap and strong, but can corrode causing fuel leaks.

Copper

[

edit

]

Older vehicles may be fitted with copper fuel pipes. These are easy to fit and repair, but copper is heavy and expensive when compared with the other options.

Fittings

[

edit

]

Traditionally fuel lines had flared or compression fittings on the rigid pipe sections, and hose clamps where rubber hoses attached to metal components. In modern cars with plastic fuel lines, quick release fittings are becoming more common – this allows the fuel system components to simply clip together.

Priming

[

edit

]

The primer bulb can be found on the fuel line between the gas tank and the carburetor.[4] When you prime the carburetor, you are pushing fuel from the carb bowl to the barrel using the rubber primer bulb.

See also

[

edit

]

References

[

edit

]