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Old 15-10-2021, 22:41   #1
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Acceptable Length of fuel hose

Hi All
I’m seeking views from those who know about fuel reticulation and particularly acceptable length of hoses.

The existing set-up has fuel drawn and returned from both tanks without any change-over option. I plan to separate the tanks by installing a set of change-over valves so I can choose which tank to draw/return fuel from.

The length of the supply line won’t change from the existing 3200mm. This is the length from tank to Racors to the engine lift pump. The only location I can come up with for the new change-over valves is next to the Racors.

The return lines are a bit different. Right now, the length of hose from engine to tank is around 1200mm. They will need to be redirected to the new valves (next to the Racors) which will increase the length to around 2500mm.
In case it’s relevant, the engine is a Perkins Prima M50 (50hp) and hoses are 5/16”.

I don’t know if this lengthening of the return line will be a problem for the fuel circulation. Any views on this or suggestions what I should investigate would be much appreciated.

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Old 16-10-2021, 05:02   #2
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Re: Acceptable Length of fuel hose

Funny, I was just going to write a post about my fuel line experience and title it "Use fuel line dummy!" ...I used about 7" (15cm) of tubing from a siphon hand pump as a temporary fix, and when I had a brief chance to go ashore and buy a short piece of 1/4" fuel line, I did, but I decided upon returning that my time was better spent doing something else other than replacing the tubing with actual fuel line. The very next day while motor sailing in heavy weather, pounding through seas on my nose and close-hauled, the engine would not run above 1100 rpm, I later figured my siphon tubing was collapsing under the suction of the fuel pump. And this is where I would suggest for the length of run you have to do, you should consider using hardline, like copper tubing, because even though your fuel pump is unlikely to collapse the fuel line, it could deform just enough on each pump stroke so as to not allow a full "pump" and if that happens you may find yourself with fuel starvation when you need full power. As far as a return line, I don't know of the system you're using, but if it's similar to an oil furnace burner pump, where the loop seems to be just for air elimination, generally the loop can be eliminated for a single-line, as long as you use a device like the Tiger Loop, this is a de-aerator. But certainly you should understand the mechanics of your system before attempting to re-engineer it. One thing I do not like about looped systems is they stir-up sludge that may have collected in the tank; but in a boat who knows, all the rocking stirs up sludge too, so it might not matter.
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Old 16-10-2021, 05:19   #3
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Re: Acceptable Length of fuel hose

Interesting and useful observations, from Lou. But, the fuel RETURN line won’t be under suction, so not liable to collapse. Nonetheless, good advice.
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Old 16-10-2021, 05:41   #4
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Re: Acceptable Length of fuel hose

Return flow is low, and pressure pushing it is high. You’ll have no problem.

I am curious, in the original arrangement, how could you be sure the return fuel was going to the same tank you were drawing from? If you leave that to chance, it’s way to easy to overflow one tank with the engine return flow when drawing from the other one!
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Old 16-10-2021, 05:49   #5
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Re: Acceptable Length of fuel hose

Quote:
Originally Posted by Lou-In-NJ View Post
As far as a return line, I don't know of the system you're using, but if it's similar to an oil furnace burner pump, where the loop seems to be just for air elimination, generally the loop can be eliminated for a single-line, as long as you use a device like the Tiger Loop, this is a de-aerator. But certainly you should understand the mechanics of your system before attempting to re-engineer it. One thing I do not like about looped systems is they stir-up sludge that may have collected in the tank; but in a boat who knows, all the rocking stirs up sludge too, so it might not matter.
He is using a standard Diesel engine with a mechanical injection pump. More fuel is delivered than the engine needs and it has to go back to the fuel tank. It has nothing in common with a oil furnace burner, and is not there for “deaerating” and a “Tiger Loop” is not appropriate.

If your S2 has a Diesel engine, you will find exactly the same arrangement of returning fuel to the tank if you look for it. You might not “like” what you call “looped” systems, but almost all Diesel engines need them and have them.
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Old 16-10-2021, 06:39   #6
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Re: Acceptable Length of fuel hose

Billkny, with the tanks combined, he's probably got rough equalization of fuel in the two, independent of where the return line goes.

My set-up is purely manual, with take-from and send-to valves for two tanks, and a Detroit Diesel engine that returns a lot of fuel. Wideocean, just be aware that when you set up a manual system, you are responsible for getting it right. The original combined system is idiot proof but does not allow you to use the tanks to trim the ballast or to isolate one tank when you get some bad fuel. The manual system lets you do all that, but also allows you (as I once did) to fill the engine room with fuel when you forget to open a return line and a hose pops....
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Old 16-10-2021, 07:02   #7
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Re: Acceptable Length of fuel hose

I would NOT use copper for a return line.
a. The pulsation observation is interesting, but as Gordo pointed out, only for pressure activated injectors.
b. Manufactures and standards organizations recommend against copper in fuel systems for reasons of fuel storage stability. We use copper where we must, but should also minimize it where there is no detriment to function.


I'm not making "b" up. Read the following links from Cat, Yanmar, ASTM, and Cummins.

Sail Delmarva: Are We the Cause of Fuel Breakdown?

This is only applicable if the fuel is in the boat for more than a year... but in many cases it is. Some times a few years. if you cruise you turn fuel over, but many of us day sail, and it only takes us a pint to clear the jetty and raise sail.


As for the OP's question, the engine will not feel this small extension to the recirculation line.
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Old 16-10-2021, 07:06   #8
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Re: Acceptable Length of fuel hose

The run from my fuel tank to my engines is over 30ft or 9144mm of fuel hose. No problems.
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Old 16-10-2021, 09:33   #9
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Re: Acceptable Length of fuel hose

IIRC, the various standards require that fuel shutoff valves NOT be located in the engine space, but rather close to the tanks and outside of a space where a fire might most probably occur. Does you "close to the Racor filter" meet that?
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Old 16-10-2021, 09:36   #10
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Re: Acceptable Length of fuel hose

Quote:
Originally Posted by BillKny View Post
Return flow is low, and pressure pushing it is high. You’ll have no problem.

I am curious, in the original arrangement, how could you be sure the return fuel was going to the same tank you were drawing from? If you leave that to chance, it’s way to easy to overflow one tank with the engine return flow when drawing from the other one!

We have the same issue. Just remember to use most of the fuel from the largest tank before switching to the other tank.
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Old 16-10-2021, 10:23   #11
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Re: Acceptable Length of fuel hose

You are going to have to install two fuel gauges otherwise you will not know when the return line has filled the tank. And that could cause you problems. Otherwise leave it as it is.
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Old 16-10-2021, 10:25   #12
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Re: Acceptable Length of fuel hose

Get a GROCO 6 port fuel selector valve, expensive, but cheaper than the fines from dumping fuel in the water if you forget to switch the return line.
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Old 16-10-2021, 10:59   #13
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Re: Acceptable Length of fuel hose

Well, 1200 mm is only 4 feet.
For return lines why not just a 3 way valve in the existing return lines?
Or really in both feed and return...
I guess I dont understand why now suddenly the return lines are much longer...
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Old 16-10-2021, 11:21   #14
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Re: Acceptable Length of fuel hose

My fuel lines to mains and generators are all much longer than 10'. (You do the math this time)
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Old 16-10-2021, 12:27   #15
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Re: Acceptable Length of fuel hose

Dear Wideocean,

Given your information, the suction and return pipe/hose lengths shouldn't be any issue at all.
A combined double three way valve for all the suction and return pipes/hoses is generally most reliable especially if operated by a stranger or non technical crew member etc.
For reliability and fire protection I'd suggest using "proper" marine fuel hoses meeting the equivalent of US Coastguard / ABYC requirements or equivalent. Those hoses are thick and basically won't collapse or burn through quickly. A very good alternative is to use SS tubing also. Also it is good practice to double clamp all hose terminations with HD marine, all SS hose clamps. Doing the best possible job that one can afford usually results in a better level of performance and reliability.

Best regards,

Niall.
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