Regan Brown
Whether fuel lines should be double flared is a matter of some debate. Some people argue that a double flare provides a better seal, while others are concerned about the possibility of cracking with a double flare on aluminium tubing. It is also noted that stainless steel is harder and more brittle than stock lines, and cracks can form at the flares if it is double flared.
| Characteristics | Values |
|---|---|
| Compression | Double flare provides a little more compression than a single flare |
| Seal | Double flare provides an even seal |
| Cracking | Double flaring can cause cracks to form in stainless steel |
| Cracking | Double flaring can cause cracks in aluminium tubing |
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What You'll Learn
Compression fittings are recommended for fuel lines
When it comes to flaring fuel lines, there are differing opinions on whether a single or double flare is best. Some people recommend a double flare, as it provides a little bit of compression from the nut/ferrel when tightened, creating an even seal. Others argue that a single flare is adequate, as a double flare can cause cracking in aluminium tubing.
It is also worth considering the type of tubing being used. For example, stainless steel is harder and more brittle than stock lines, and it is not recommended to double flare stainless steel as cracks tend to form at the flares. In this case, it may be better to route a new line, leaving the old one in place, rather than attempting to repair it with a double flare.
Ultimately, the decision of whether to use a single or double flare, or compression fittings, may depend on the specific vehicle and the accessibility of the fuel lines. For example, trucks often have fuel lines attached to the inside frame rails, making them easily accessible. In this case, a single flare may be sufficient, as there is no need to create an extremely tight seal.
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Double flares are not recommended for stainless steel
Single flares are considered adequate by some, while others argue that double flares provide a better seal. However, there is a concern about possible cracking with a double flare on aluminium tubing.
One user suggests using compression fittings for fuel lines, as gasoline is tough to seal. They also recommend doing a double flare on mild steel lines.
Another user mentions that with an AN flare nut, there is an additional insert that eliminates rotational rubbing against the back face of the flare when tightening. However, they also state that there is no reason to do a double flare in this situation.
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Cracks can form with double flares
One user on a forum said that they had always thought that the double flare had a little bit of compression from the nut/ferrel when tightened down, giving an even seal. They did a test on a piece of 3/8" fuel line and did a double flare to see if the ferrel and nut would fit, and they seemed fine.
However, another user on the same forum said that they could see the surface stress fracturing at the folded bend. They said that this is not nearly as severe with soft copper or stainless steel.
Therefore, while cracks can form with double flares, it is important to consider the type of tubing being used and to test the double flare to ensure that it is secure and will not leak.
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Double flares can cause surface stress fracturing
However, some people have found that using a double flare on mild steel lines is fine. One person said that they always thought that the double flare had a little bit of compression from the nut/ferrel when tightening it down, giving an even seal. They tested this by taking a piece of 3/8" fuel line and doing a double flare, and found that the ferrel and nut seemed to fit just fine.
Another person said that they would use compression fittings, which they do all the time in their shop. They recommended doing a double flare on mild steel lines.
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Single flares are adequate
One user points out that double flaring can cause surface stress fracturing at the folded bend, which is not as severe with soft copper or stainless steel. This suggests that single flares are a more durable option for certain materials.
Another user notes that there is "no reason" to do a double flare, and that double flaring can cause the flare to become tilted and out of alignment. This suggests that single flares are simpler and less prone to error.
While some people argue that double flares provide a better seal, this does not seem to be borne out by the evidence. Single flares are therefore a perfectly adequate option for fuel lines.
Frequently asked questions
It depends on the material of the fuel line. Double flaring is not recommended for stainless steel as cracks tend to form at the flares. It is also not recommended for aluminium tubing as it can cause cracking.
Single flaring is an alternative to double flaring. Single flaring is perfectly adequate and can prevent cracking.
Compression fittings are another alternative to double flaring. They are acceptable for fuel lines but not for brake lines due to the extreme pressures.
Double flaring can provide an even seal as it has a little bit of compression from the nut/ferrel when tightened.
