It's just an observation, but the discussion originally
on the fuel lines drifted into that of brake lines too.
For the fuel line I would suggest that plain old copper
tube is fine, but for the brakes the Copper - Nickle
(Kunifer) should be used due to it's higher stress
resistance.
The reason for this is that copper (and most metals)
"work harden" over time under repeated stress,
become brittle (it's almost a crystalisation process)
and finally breaks when it reaches an "elastic limit"
under what would be a ridiculously low breaking
stress when new. You can experienc this by just
repeatedly bending say, a welding rod about the
same point. You will notice it gets easier each
time until it finally breaks at that point. It is a
form of "stress fracture" and you can also feel
the heat generated at the break point!
Now the fuel line is not subject to much stress, it
just sits in place and fuel flows gently through it.
Any movement in the pipe is easily taken up well
within the elastic limits of the copper by the radii
of the pipe's bends and so there is no problem.
The brake pipes however are subjected to a most
considerable stress due to the very high brake fluid
pressures generated each and every time we hit
the brakes, and though the physical movement this
causes is small, the STRESS induced is high. The
result over time is work hardening, crystalisation,
and eventual catastrophic failure probably under
braking and with a very slight physical distortion
caused by heavy chassis movement shuch as hitting
a pothole or mounting a kerb.
.
So for fuel lines - Copper is OK and Kunifer is
an overspecification but just as good, but for the
Brake lines - you definately should use a more
stress resistant Copper - Nickle alloy tubing such
as Kunifer.
Clive
Oxford UK
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Mg-t@autox.team.net
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