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Old 29-09-2017, 21:34   #1
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help with fuel line fittings - diy steel lines

Hi all - So after spending 3 hours running around today to hardware stores ive decided to heck with it.. I want to make my own steel fuel lines..

Firstly I dont mind using brake line steel (i know it will rust eventually) but the coated ones shd last a while. What other options do I have (apart from ss). Would the mixed alloy ones be ok? what about brass?

Secondly - id like to order like 6 of each type of popular carb fittings to flare.. im stuck somewhere between what appears to be 1/8 on the 12v elec pumps, 1/4 on smaller carbs -

Its a very ambiguous realm - depending on line size, fitting size and then the sizes make NO sense! a 1/8 looks about as think as a 1/4 -

Then there are compression types (like a brake line) - and some that seal on the thread (npfs or something)?

Does anyone have first hand knowledge what the common sizes are for gas carbs/pumps?

thanks and sorry for any ignorance on my part!
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Old 30-09-2017, 03:24   #2
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Re: help with fuel line fittings - diy steel lines

i have 8mm copper tube throughout for a 33hp vetus,with 8mm id flex fuel hose held on with hose clamps

for my 144 hp volvo,same setup using 10mm copper tubing.

long runs of copper tube need regular supports.

hose barbs,corner fittings,tube etc i get from a hydraulic hose and fitting company locally. Armada 24, order online before 10pm for next day delivery on hydraulic fittings and accessories. Full range of quick release couplings,

i have a hand bender for shaping the tube,inexpensive,and prevents kinks.

i would not use mild steel tube as it will rust very quickly in a marine environment

installation is for diesel,petrol would require a much higher standard if diy
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Old 30-09-2017, 04:53   #3
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Re: help with fuel line fittings - diy steel lines

FWIW, I used 8mm (5/16") stainless steel tube for my diesel lines (2GM20) bent with a hand bender and 8mm fuel hose and hose clamps on the ends. being working now for 10(?) years.
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Old 30-09-2017, 07:54   #4
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Re: help with fuel line fittings - diy steel lines

Tx guys, seems copper is the more workable material.. No long runs, usually on io's, 5ft Max.. Ss is ideal but can't flare without pricey stuff..

Uscg requires fuel lines after pump to be metal..
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Old 30-09-2017, 08:58   #5
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Re: help with fuel line fittings - diy steel lines

Copper isn't recommended for use with diesel. Use steel.

"Do not use copper tubing for diesel fuel lines. Diesel fuel polymerizes (thickens) in copper tubing during long periods of standby and will clog the fuel injectors."
Diesel fuel piping? - Pipelines, Piping and Fluid Mechanics engineering - Eng-Tips
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Old 30-09-2017, 11:24   #6
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Re: help with fuel line fittings - diy steel lines

NONE OF THIS APPLIES TO ATTEMPTING TO FAB-UP YOUR OWN FUEL INJECTION LINES.
I have built double flare lines from copper, steel, stainless steel and monel which is a copper nickel alloy.
Monel is the easiest to work with using readily available tooling and produces good flares. Extremely durable in a salt water environment.
Stainless steel is the worst material to work with. Depending on where you are, double flare could be foreign to you but by for they produce the best leak-free sealing without some additional sealing material.
My recommendation is that no matter what type of connection you are making use as much bronze as possible for fittings and monel for lines.
Do not spend good money for junk tooling, The American company RIDGID is probably a minimum standard for tube/pipe work.
Good luck with your project.
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Old 30-09-2017, 11:41   #7
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Re: help with fuel line fittings - diy steel lines

hi thanks ill stick to copper/bronze or brass fittings.. Yes i am currently shopping round for a good blue point or mac/snap on set.. i dont use junk for stuff like this.. yes ss is impossible to flare without a very high dollar tool..

its more the darn fittings im not familiar with.. I presume there are fittings that seal on the thread alone and are angles at the bottom (like a brake line).. If i remember correctly my ford 351w pump is like this.. just threads - so sealing up to that requires the correct thread/fitting.. I might be wrong, have to get to the boat again
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Old 30-09-2017, 15:56   #8
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Re: help with fuel line fittings - diy steel lines

Quote:
Originally Posted by Terra Nova View Post
Copper isn't recommended for use with diesel. Use steel.

"Do not use copper tubing for diesel fuel lines. Diesel fuel polymerizes (thickens) in copper tubing during long periods of standby and will clog the fuel injectors."
Diesel fuel piping? - Pipelines, Piping and Fluid Mechanics engineering - Eng-Tips
This may be a theoretical problem, but in practice... well, I've used copper fuel lines for diesel for the last 32 years without any sign of the alleged problem. Longest period of stagnation was 7 months... maybe the quote refers to much longer periods, like multiple years. Not gonna be a problem in most yachting applications.

The issues with steel tubing in a marine environment have already been raised.

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Old 30-09-2017, 16:35   #9
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Re: help with fuel line fittings - diy steel lines

In our boat some lines, closer to the tank, look like either bronze or copper (I cannot tell the difference) while others (closer to the engine) look like soft steel (non SS, clearly). There is rubber in between them (from the primary filter to the priming pump).

Our engine is 13hp only and the lines are small - way smaller than 8mm, maybe 5mm max.

I did not know monel is used.

Are monel tubes easy to buy?

b.
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Old 30-09-2017, 18:00   #10
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Re: help with fuel line fittings - diy steel lines

ive been reading about this nicop stuff - apparently VERY corrosion resistant, flexible and very strong.. so ill be ordering some of that for work.. apparently vw,audi and a bunch of car manufacturers use this as oem material..
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Old 30-09-2017, 18:12   #11
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Re: help with fuel line fittings - diy steel lines

Not completely sure of your application here, but if you've got a Mercruiser with a mechanical pump, and are replacing it with an electric pump, my first question would be why? The mechanical pumps are at least as reliable as the electric, in my experience more so...

If you are planning to remote mount the pump, i.e. not on the engine, this is probably not a good idea, and may also be against USCG rules. (a remote mount pump could continue to pump gas if an engine fire compromised a fuel line on the engine, for instance).

Mercruiser just uses regular steel double flared lines, I think 45 degree, but don't hold me to that without checking. I have used 3/8" (OD) copper lines single flared with a hardware store flaring tool for personal applications on Mercruisers, but you're not supposed to, the copper is said to be subject to vibration-induced cracking.

The main difference (at least in the US) for flared fittings is the flare angle, generally 37 or 45 degrees. If you know the tubing size and the flare angle, a knowledgeable parts person will be able to steer you right as far as fitting selection is concerned...

As for sizing, the (very) general rule is that the relevant dimension is used for sizing; structural 'tubing' is measured by the O.D. because that is the dimension used for load calculations and fabrication specs. Fluid-carrying tubing, pipe, is measured by the I.D., because that dimension determines the flow characteristics

You can get a very good double flaring tool, probably way more than you'll ever need, for less than 200.00. You can also probably get one that will do double flares good enough for your needs, for less than 50.00.

If you're making lines, steel, ss, or copper, to fit an engine mounted pump/carb system, an inexpensive, mandrel-type tubing bender will make the job much easier and yield more 'professional' looking results...
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Old 01-10-2017, 06:29   #12
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Re: help with fuel line fittings - diy steel lines

Just a thought, but have you tried a local FBO (aviation fixed base operator)? They should have access to all types of AN fittings and Aeroquip steel braided hose or the tubing required for your project. Not once have I heard anyone suggest the use of aluminum tubing for this application. Aluminum is easy to double flare and bend, just remember to allow for vibration, expansion, chafing, etc. when using any tubing. Just a thought.
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Old 01-10-2017, 15:23   #13
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Re: help with fuel line fittings - diy steel lines

Quote:
Originally Posted by Terra Nova View Post
Copper isn't recommended for use with diesel. Use steel.

"Do not use copper tubing for diesel fuel lines. Diesel fuel polymerizes (thickens) in copper tubing during long periods of standby and will clog the fuel injectors."
Diesel fuel piping? - Pipelines, Piping and Fluid Mechanics engineering - Eng-Tips
I use only stainless steel tubing for all marine applications whether gas or diesel.
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Old 01-10-2017, 16:11   #14
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Re: help with fuel line fittings - diy steel lines

If it is not on the actual engine most use copper and flare tools.
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Old 01-10-2017, 17:18   #15
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Re: help with fuel line fittings - diy steel lines

The end of the fitting that threads into a carb or fuel pump or filter housing is often an ORB fitting and sometimes a NPTF, the other end of that fitting is often a JIC also referred to as a flare fitting. NPTF or NPTC is "National Pipe Thread fine" for the former and" course" for the latter. You can find charts and gauges to determine size on line, just google it. ORB seals with a O ring, NPT needs a sealant compatible with what you are pluming and JIC uses pressure at the beveled surface to seal.
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