How "flexible" is copper fuel pipe?

[RobBrown]

Replacing an agglomerator with a CAV filter/bowl, which has four ports (in & out on both sides, with 2 blanks) instead of two on the original (one in one out). The in port feed (ie from tank into the new unit) is on the outside of the head unit, so is about 1 1/2 - 2" further out from the bulkhead than the current fitting. There is little fore and aft movement of the connected pipe in the exisiting set up and I am worried that moving the pipe laterally out onto the fitting on the new head might stress it unduly. Any opinions, advice or suggestions? (It is copper fuel pipe from the tank right up to the nut union on the agglomerator, no flexible pipe work)

 

[prv]

If you have enough "slack" to put a double bend in it (using correct tools to avoid flattening) so that it runs naturally to the new place, I'd have thought it would be fine. I made some really rather tight bends in copper tube to build my double-filter manifold. The point is that the ends should fall naturally onto the fittings, not be pulled over to them so that they really want to spring back.

Not sure whether you have the necessary slack or not.

Pete

 

[VicS]

You don't say what diameter but copper pipe bends very easily provided it has not been work hardened.

Even when work hardened you will probably be able to bend it sufficiently to match up with the connections on the new filter.

Bend it so that it naturally lines up with the new fittings rather than just springing it out into position. Make sure the ends of the pipe line up with the connections on the filter correctly as prv says.

If necessary you could consider annealing the pipe where you need to bend it if it has hardened.

 

[RobBrown]

Thanks for replies. I think it is 8mm pipe. Oldish (certainly pre-dates my 5+ yr ownership). The ports are 1/2" threads. I assume I would need something like a spring pipe bender to try & re-position? Certainly at present, simply moving to the outer port would be at angle and under tension.

 

[VicS]

A quick Google tells me that for small diameter pipe (<10mm) you can use a bending spring that fits around the outside of the pipe but I've never seen one. The internal ones do exist though for 8mm

I would not even have considered using a bending spring unless I wanted some sharp bends. I'd bend it gently just by hand.

It's possible you may have to cut back and join a new section on if its too short, or replace the whole length(s) if they are fairly short.

 

[catmandoo]

A quick Google tells me that for small diameter pipe (<10mm) you can use a bending spring that fits around the outside of the pipe but I've never seen one. The internal ones do exist though for 8mm

I would not even have considered using a bending spring unless I wanted some sharp bends. I'd bend it gently just by hand.

It's possible you may have to cut back and join a new section on if its too short, or replace the whole length(s) if they are fairly short.

you can get a tool to bend both 8 mm and 10 mm pipe . Its steel and has two grooves on a quadrant one for each diameter . There are two handles and you rotate one against the other eover the required arc

Simples

 

[Babylon]

Replace with flexible hose?

...It's possible you may have to cut back and join a new section on if its too short, or replace the whole length(s) if they are fairly short.

Can you not replace the copper piping altogether with flexible hose? After all, if the correctly-rated heavy-duty hose is used to supply fuel from the filter to the engine, why cannot it be used from the tank to the filter?

 

[prv]

A quick Google tells me that for small diameter pipe (<10mm) you can use a bending spring that fits around the outside of the pipe but I've never seen one.

you can get a tool to bend both 8 mm and 10 mm pipe . Its steel and has two grooves on a quadrant one for each diameter . There are two handles and you rotate one against the other eover the required arc

I used all three (internal spring, external spring, and a homemade wooden version of the grooved tool) to bend different bits of my manifold.

Pete

 

[RobBrown]

I think I'll try bending by hand at first then and if no joy, I'll probably go for a longer replacement pipe made up for me as likely little difference in costs of purchasing bending devices to do the job and I am more certain of getting a proper fit. It was as usual trying to go for the lowest cost solution and then finding it isn't that simple!

I did ask a similar question to Jon's (Babylon's) in the past as when I had my major fuel pipe fracture last year, the engineer fitted a replacement flexible pipe from the engine filter to injector pump, but advised this was a temporary measure to get me back to the home mooring & came back later & fitted a replacement fixed pipe ( & charged again accordingly!). Never really got a clear answer about relative suitability.

 

[prv]

I think I'll try bending by hand at first

Just be careful you don't fold the pipe at the bend so that it ends up kinked. I find it easier to "roll" it round something of suitable diameter, with a stretching, pulling motion rather than just forcing it sideways.

I did ask a similar question to Jon's (Babylon's) in the past as when I had my major fuel pipe fracture last year, the engineer fitted a replacement flexible pipe from the engine filter to injector pump, but advised this was a temporary measure

Well, it's standard fit on Yanmar GM engines.

Pete

 

[RobBrown]

Pete

Thanks for the tips- first time for everything!

I think in light of your comments re use of flexible pipe, my remark re charging twice might offer the best "technical" justification!!

 

[prv]

I think in light of your comments re use of flexible pipe, my remark re charging twice might offer the best "technical" justification!!

I think that might be a bit harsh. If I were a conscientious professional mechanic I would want to repair things in the proper manner, including replacement with manufacturer's (or third-party but designed for the job) spares. Leaving the customer with an ad-hoc modification would be a bit cowboy, even if in practice it's unlikely to give any trouble.

At most you might hope he would explain the situation and let you decide whether to properly repair or continue with the lashup.

Pete

 

[NormanS]

Copper, unlike steel is, annealed (softened) by heating to less than red hot, and then plunging into cold water. If you do this you'll find that you can bend it very easily. A gas torch or the kitchen hob, will do the job nicely.

 

[nedmin]

heat the pipe to dull red, just go down the pipe with a blow torch,you will see it go rainbow colour as you do it. Fill with dry sand make sure pipe is full of sand,push a bit of wood in each end and you will bend it easily round a piece of pipe .Obviously you will have to wash it out well when youve done.the pipe will return to its original hardness in a short time.

 

[nedmin]

Forgot about cooling with water as Norman S said. You will be able to put a "coil" in it which will stop fracturing.

 

[VicS]

Copper, unlike steel is, annealed (softened) by heating to less than red hot, and then plunging into cold water. If you do this you'll find that you can bend it very easily. A gas torch or the kitchen hob, will do the job nicely.

It is sufficient to heat to dull red ( no more) and allow to cool.
Although for many years I always did quench in water is not in fact necessary.

It is important though not to overheat the copper or keep it at the annealing temperature for a prolonged period.

 

[NormanS]

It is sufficient to heat to dull red ( no more) and allow to cool.
Although for many years I always did quench in water is not in fact necessary.

It is important though not to overheat the copper or keep it at the annealing temperature for a prolonged period.

Actually, I've found this too, and was quite surprised, but I do normally quench in water. Isn't it strange that copper behaves in exactly the opposite way to steels.

 

[VicS]

Actually, I've found this too, and was quite surprised, but I do normally quench in water. Isn't it strange that copper behaves in exactly the opposite way to steels.

I think with copper its just a question of heating it to allow the crystal structure to reform. Once its back to normal it does not matter how slowly quickly it cools there are no changes that can occur as the temp falls.

You only have to look at the phase diagram for iron and carbon to realise that steels are likely to behave in a complicated way. Quenching tends to freeze the structure at one which is stable at elevated temperatures. In the case of steel thats one which is hard. Cooling slowly allows the structure to change to a softer one that is stable at lower temperatures. Heat treating steels is a complex subject though.

I learnt a bit of metallurgy once. I can just about manage to follow the first chapter on heat treating steels in my old textbook but I don't pretend to understand the second one now! I'm glad I learnt the bit of metallurgy I did. It's given me a bit of insight into the subject.
The alternative was bacteriology

 

[Alpha22]

I've just done a similar job and also replaced a fuel line. 8mm copper. I got an external bending spring of ebay for about £3.50 It did the job a treat. Well worth it.
I have a motto of always use the right tool for the job. Especially if it is only £3.50!! Not only have I done a job that I can be proud of, I have a new tool for the tool box.

 

[prv]

I'm glad I learnt the bit of metallurgy I did. It's given me a bit of insight into the subject. The alternative was bacteriology

What on earth were you studying that had both metallurgy and bacteriology as options?

Mind you, I can't talk, I did basic Russian as a module of a Computer Science degree

Not only have I done a job that I can be proud of, I have a new tool for the tool box.

I've still got the (internal) springs from my bending job, but I was making such tight curves that the springs themselves are irrevocably bent into spirals and won't go into the tubes any more!

Pete