Fuel pipe - braised end

[huldah]

Perkins 4108

I recently had to repair leaking fuel pipes on a fairly old boat. The ends of the pipes at the tank tap and the fuel separator had tapered, braised ends. The output from the separator should have had the same fitting. By drilling the centre so the pipe could enter the joint, I was able to fit an olive. This was successful, however I would appreciate views on the following.

Is the braised system superior? Are the ends available, and from whom. Lastly, the pipes were made of steel, is this correct?
Thanks, Philip

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[Talbot]

olive should be superior to a braised end. most tapered joints are made from the existing pipe with a tool that bells out the end. Soldered joints (and presumably braised as well) are not a great idea for the fuel line (and are illegal for the gas) cause in a fire, the solder/braising will fail and dump more fuel into the fire.

Your bio does not say where you are, but most cities have a shop that specialises in brake and fuel line and they would be able to supply the correct copper or the new composite lines. alternatively you can source them from ASAP.

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[VicS]

Re: What\'s cooking?

I'm sorry I couldn't resist this one. I hope you mean brazed rather than braised!

I take your point about soldering. The melting point of solder is quite low, most alloys starting to soften at around 183C, although there is a tin, lead, antimony alloy for soldering iron an steel which has a melting range of 243 to 250C. Solder is also pretty weak. Silver solders are better in both respects and true brazing, with a copper zinc alloy, is better still. These alloys have melting points in excess of 750C.

I think you'll find brazed joints would be acceptable, on gas systems as well, as the joint material will most likely consist of a straight forward alpha brass which is both tough and ductile. I see no problems with a compression joint with an olive though and they are easy to do whereas brazing needs a suitable torch, rods, flux and a little skill.

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[Gunfleet]

Boeuf en daube! NM

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[mirabriani]

Re: What\'s cooking?

Agree. This is why brazing is specified on air condition systems.

Briani

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[pappaecho]

The tube is probably "bundy tube" and should be available from most automotive brake parts suppliers.
The problem with brazed tubes is that they case harden and fracture with vibration over time.. what was the cause of the leak in the first place? I would definitely prefer compression olives, as they have a degree of "give" and are not so likely to fracture with vibration.

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[huldah]

Hi folks,

Thanks for the replies.

I live in Bath and have updated my profile. Sorry about the spelling! None of the places I visited recognized the ends. These included boat yards, factors, and a fuel injection company.

I am quite satisfied with my repair, so have no urgent need for the ends. It was mainly that I was intrigued, as I thought they may be superior. The pipes had previously been bodged. The separator output pipe had been fitted with an olive, but as it could not enter the small hole, it swivelled around. I drilled this to take the pipe, leaving the original mating parts undamaged. The bottom of the flexible pipe was jointed to a copper pipe with a joint meant for a smaller pipe. This fell apart in my hands. The fuel pipe was bent in all direction, pulling sideways on the joints. All now neat and tidy.

For the first time we have an engine that runs properly, even though the top of the upper injector pump bleed screw is missing.

Philip

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[cliff]

And where did you study Metallurgy?

Brass "case hardening" due to vibration - I think not. If you are going to make emphatic statements at least get your facts correct. You will find it is the pipe/tube that generally fails and the main reason for the failure is poor fitting rather than the type of coupling.

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[Avocet]

The only thing I'd be a bit worried about is the fact that the fuel line is steel. Normally, "olive"-type compression fittings use the torque applied to the nut to squash the brass olive on to a copper or copper-nickel pipe. The copper is very soft so you don't need to tighten the nut up that much to get a good seal. Even so, a few years ago, I replaced some compression "T" fittings on a gas installation and was mightlily miffed when I came back the following week to find a gas leak. (ironically, the reason for the work in the first place was to fit a bubble leak detector!) Anyway, one of the brass nuts had split. I replaced it and the following week, ANOTHER of the nuts had split! I then decided to replace all the "T" pieces bought from this supplier as a matter of course! I kept them in the garage though, with the nuts tightened on to the stumps of the copper pipe and over the next 6 weeks or so, EVERY DAMNED NUT SPLIT!!!!!

So I think what I'm saying, is that you might have had to tighten them a fair bit to get enough force to crush the olive into the steel. If that's the case, it might be worth periodically checking them for leaks for a few months just in case they end up doing what mine did!

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