What diameter copper fuel pipe for 50hp diesel?

contessaman

contessaman

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Need to run some copper fuel line from a tank to engine bay, and injector return back to tank. What size copper pipe should be used? 50hp mermaid diesel 1.8 litre naturally aspirated. The last few feet to the engine will be 8mm I.d. flexible rubber fuel hose.

Seems like 8mm or 10mm o.d. is the choice. Concerned the I.d of the 8mm o.d. pipe could be too small and concerned the 10mm stuff will be a pain in the backside to bend and route about the place.

Thoughts? What do you have on your boat? Thanks
 
https://www.asap-supplies.com/hose/copper-nylon-piping/copper-tube-10m-coil-302114

Something like this be okay then? It says 1mm wall thickness so the internal bore will be 6mm. Is that enough? For sure the the actual consumption is only about 3-4 litres an hour at cruise, but I don't have a feel for how much extra the injector pump will take and then feed back to the tank.. Presumably many more litres than this. My motor doesn't have a fuel lift pump either - its built into the injector pump... Don't want to knacker it by making it work to hard.
 
8mm for the flow & 6mm for the return should be fine unless the runs are very long.We operated BMC 2.5 on a commercial boat for over 10 years on 1/4" copper about 5ft run,never any problem & similar HP

Jim
 
One boat builder used to routinely install half inch steel galvanised pipe to alongside the engine, then spec size to the lift pump. If a valve is fitted there you can then disconnect and get a good flush through in the event of a problem. You get a good flow, but if you are drawing fuel over the top of the tank it might be a problem to prime.
 
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jamie N said:
If you're planning to use any copper in a diesel system, this might be worth a read, in the section marked 'Accelerated Ageing':

ACCELERATED AGEING
The ageing process can be accelerated by the following conditions:-
• Contact with zinc, copper or metal alloys containing them. These metals will quickly
react with diesel fuel to form unstable compounds.

https://www.bp.com/content/dam/bp-country/en_au/media/fuel-news/long-term-storage-diesel.pdf
Click to expand...

That paper is about storage of fuel rather than delivery through short fuel pipes but, if it still applies, then there are a hell of a lot of boats out there running well on unstable compounds.
 
jamie N said:
If you're planning to use any copper in a diesel system, this might be worth a read, in the section marked 'Accelerated Ageing':

ACCELERATED AGEING
The ageing process can be accelerated by the following conditions:-
• Contact with zinc, copper or metal alloys containing them. These metals will quickly
react with diesel fuel to form unstable compounds.

https://www.bp.com/content/dam/bp-country/en_au/media/fuel-news/long-term-storage-diesel.pdf
Click to expand...

Crumbs that's not a good thing to read! That said, every boat I've ever had used copper for most of the run and flexi hose for the last bit to the engine... Never had problems before.

However the main thrust of that article is the reason why I'm changing things aboard my boat. The rassy 38 has a 220 litre grp tank in the keel which feeds the engine/heating Then a 140 litre 'reserve' stainless tank under the port saloon berth which can sluice into the main. With the amount of use the boat normally gets around my work pattern that much fuel capacity means the fuel is likely to sit there for 5 years or more. The keel tank is a pain in the *** to keep clean. I'm not convinced its great for the hull either- forming one side of a fuel tank permanently immersed in fuel.

I'm modifying things so that the engine and heating will run off the smaller stainless tank, which should then get a reasonable turn over. I'll then drain the keel tank in due course. Give it a damn good clean out and fit it with an electric pump so it can be pumped up (through a filter) into the smaller tank. Hopefully this system will enable me to leave the keel tank completely empty and clean normally, and have a decent turn over of fresh fuel in the smaller one. Then, when time permits ocean crossings/extended time living aboard the 'bunker tank' in the keel can be filled also. I'll have to look at the trim of the boat with the keel tank empty and see if it needs the lid left off it and filled with pebbles or lead ingots when the boat is being used for coastal passages or island hopping.
 
PCUK said:
I'm installing a 250hp engine and 8mm I.d. Is specified so 6mm should easily suit your 56hp. Same size for feed and return is also essential.
Click to expand...

That's incredible I never would have thought 8mm I.d. could keep up with a 250hp engine. Like you said, by interpolation it should mean 8 o.d./ 6 I.d. should be fine for my comparatively tiny lump. Yep was planning on using same diameter for return as feed - only have to buy one reel of copper pipe then. I guess the run is about 12 to 13 feet from the stand pipe on the tank to the separ gemini filters on the firewall of the engine room. Was going to copper pipe that all the way then flexible hose it from the separ filters to the cav filter that's mounted on the engine. I.e. the bits that don't move copper pipe, the bits that connect the bits that don't move to the bits that do - rubber pipe.

Does that sound reasonable? Any better way of doing it? Surely not rubber pipe all the way?

I'm all ears. Lots of work to do anyway with these changes so I might as well do it as well as possible!

Thanks for all the inputs so far guys
 
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I've seen other references to the unsuitability of copper fuel pipe but, as all the installations I've ever seen are copper,have concluded that it is unnecessary scare mongering.
jamie N said:
If you're planning to use any copper in a diesel system, this might be worth a read, in the section marked 'Accelerated Ageing':

ACCELERATED AGEING
The ageing process can be accelerated by the following conditions:-
• Contact with zinc, copper or metal alloys containing them. These metals will quickly
react with diesel fuel to form unstable compounds.

https://www.bp.com/content/dam/bp-country/en_au/media/fuel-news/long-term-storage-diesel.pdf
Click to expand...
 
contessaman said:
That's incredible I never would have thought 8mm I.d. could keep up with a 250hp engine. Like you said, by interpolation it should mean 8 o.d./ 6 I.d. should be fine for my comparatively tiny lump. Yep was planning on using same diameter for return as feed - only have to buy one reel of copper pipe then. I guess the run is about 12 to 13 feet from the stand pipe on the tank to the separ gemini filters on the firewall of the engine room. Was going to copper pipe that all the way then flexible hose it from the separ filters to the cav filter that's mounted on the engine. I.e. the bits that don't move copper pipe, the bits that connect the bits that don't move to the bits that do - rubber pipe.

Does that sound reasonable? Any better way of doing it? Surely not rubber pipe all the way?

I'm all ears. Lots of work to do anyway with these changes so I might as well do it as well as possible!

Thanks for all the inputs so far guys
Click to expand...

From experience 6mm bore will be fine. I have rubber all the way, 2.5m, plus return, of ISO 7840 marked hose, and that is on an RCD CE marked boat from new. It does mean you have less potential leaks from joins.

Www.solocoastalsailing.co.uk
 
ghostlymoron said:
I've seen other references to the unsuitability of copper fuel pipe but, as all the installations I've ever seen are copper,have concluded that it is unnecessary scare mongering.
Click to expand...

I've heard of a few people complaining of black tarry deposits in diesel systems.
Diesel may not be what it once was.
Particularly if you end up buying white stuff in that Europe....
 
TNLI said:
Zinc plated Copper is better and not much more expensive than normal Cooper.
Click to expand...

I'm afraid that Zinc is even worse than Copper at promoting (ie acting as a catalyst for) reactions in ULSD, producing insoluble gels and Asphaltene.

PS: I've found that the white diesel with 5% FAME to have less Asphaltene deposit than red 'marine' diesel bought in the UK. I suspect that FAME is a good solvent.
 
jdc said:
I'm afraid that Zinc is even worse than Copper at promoting (ie acting as a catalyst for) reactions in ULSD, producing insoluble gels and Asphaltene.

PS: I've found that the white diesel with 5% FAME to have less Asphaltene deposit than red 'marine' diesel bought in the UK. I suspect that FAME is a good solvent.
Click to expand...
Only if it's underwater like a Zinc anode, most good marine engineers use Zinc plated Copper for very good reasons, the main one of which is that bare Copper turns green in salty air. If the fuel line finished up underwater, the Zinc would just act as an anode protecting the Copper. I do use Copper for fuel lines when rebuilding an engine, but normal pant it with a 2 coat clear epoxy that is as heat resistant as a normal enamel used for the engine block top coat.
With some fuel line jobs I tend to prefer using stainless steel braided flexible fuel hoses, although you do need to make sure the rubber compound is thick enough or it can fail fairly quickly. The better quality braided fuel lines do have the correct BS certificate required by some canal, lakes or river safety inspectors or insurance surveyors.
 
Ok, I think we were at cross purposes! Zn outside the pipe is just fine, I thought you meant a Zn coating on the inside, and thus in contact with the fuel.
 
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