Jump to content

8mm to 10mm copper fuel pipe


Featured Posts

Another quick question. The fuel pipe for my Bukh DV36 is a combination of 8mm copper and rubber pipe to the injectors. Will I cause any problems replacing the 8mm copper with 10mm copper. Logic says no but I'd appreciate advice.

Thanks

Link to comment
Share on other sites

No. I replaced by rubber leak off pipes by silver soldering something like 2mm ID copper pipe into the banjos. The only think that may cause you problems are getting banjos, like the one of the injector pump etc. and the correct unions for the lift pump. The injector pipes them selves will be steel, not copper, and copper is not suitable for those three pipes.

Link to comment
Share on other sites

Thanks Tony, fortunately It's not the pipes at the injectors or pump end, it's more the supply from the fuel cut-off tap to the first filter & the return pipe.

 

Link to comment
Share on other sites

3 minutes ago, Clodi said:

Thanks Tony, fortunately It's not the pipes at the injectors or pump end, it's more the supply from the fuel cut-off tap to the first filter & the return pipe.

 

The no problem as long as the unions fit the new pipe.

Link to comment
Share on other sites

9 hours ago, Ex Brummie said:

 

I would be a bit careful about those because I seem to recall "plumbers'" tube is sized differently to coiled soft copper pipe. Hopefully someone who knows will confirm of deny.  I think it is to do with wall thickness.

Link to comment
Share on other sites

Would seem to be a pointless exercise, 8mm (or 5/16", only 7 thou" difference) is adequate for the fuel lines.

Soft coiled 10mm for microbore heating circuits is 10mm OD. Much refrigeration and gas soft coiled is still imperial, 3/8" OD. 

Link to comment
Share on other sites

I suspect that OP is considering 10mm as it is more readily available in small quantities than 8mm. "Plumbers" 10 mm soft coiled coper is the go to material for oil tank supply pipework for heating applications.

The smaller gauge would be preferable as it would perform better supplying a lift pump under suction.

Edited by Ex Brummie
Link to comment
Share on other sites

29 minutes ago, Ex Brummie said:

I suspect that OP is considering 10mm as it is more readily available in small quantities than 8mm. "Plumbers" 10 mm soft coiled coper is the go to material for oil tank supply pipework for heating applications.

The smaller gauge would be preferable as it would perform better supplying a lift pump under suction.

 

Can you explain that because I think we have had this before and the general consensus was that it is nor correct. The ability of fuel to flow through a pipe is a function of the pressure difference between each end and what one might call "friction" in the pipe. The pressure difference will be the same for both pipe sizes but the larger bore pipe should allow a greater cross section of laminar, and thus lower "friction" flow, so the potential flow rate should be greater. However I very much doubt the differences between 8 and 10mm will be measurable unless using lab type equipment.

 

Edited to add: Also, as a lift pump is more or less a fixed volume per stroke pump the larger bore pipe should result in that fixed volume of fuel moving at a slower speed so that should reduce the turbulent flow as well.

Edited by Tony Brooks
Link to comment
Share on other sites

The transfer of a liquid through a pipe under gravity is better through a bigger bore as the frictional resistance is less. However, if you are inducing the supply with a vacuum, as in a lift pump, the pump will suck better through a smaller bore as the increase in frictional resistance is negated by the weight of the medium. An analogy is comparing drinking a liquid through a drinking straw, or through a length of 22mm pipe. You would have to suck a lot harder.

Having said all that, given the distances and volumes involved in a boat, then the difference would be next to neglible.

Edited by Ex Brummie
Link to comment
Share on other sites

3 minutes ago, Ex Brummie said:

The transfer of a liquid through a pipe under gravity is better through a bigger bore as the frictional resistance is less. However, if you are inducing the supply with a vacuum, as in a lift pump, the pump will suck better through a smaller bore as the increase in frictional resistance is negated by the weight of the medium. An analogy is comparing drinking a liquid through a drinking straw, or through a length of 22mm pipe. You would have to suck a lot harder.

Ignoring the friction in the pipe, your mouth would have to generate the same amount of negative pressure to suck liquid up from a lower level into your mouth in either case. The only difference is that with 22mm pipe you would have to suck a lot more air through intitially to get to the first taste of liquid. But once the pipe/straw is fully charged with liquid it makes no difference.

  • Greenie 1
Link to comment
Share on other sites

Thanks everyone, my main reason for asking is that I'm re-jigging my engine bay and the fittings on my 'Fuelguard' are 10mm my original fuelpipes are 8mm & I have a spare coil of 10mm copper left over from fitting 2nd fuel tank for the Heritage Uno.

 

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.