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Old 11-08-2022, 02:14   #1
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Diesel return line setup

Hi all,

A friend and I are looking at fuel return line setups. Both of us have tanks where the return line comes to the top of the tank and the returned fuel ďfree fallsĒ to the fuel level. Not far, a few hundred mm at most.

We wondered if this was a problem and I remembered the diagram in the Beta 50 manual which seems to introduce a lot of complication. I assume thereís a reason for this setup. Can anyone explain the rationale, beyond the somewhat ambiguous language in the manual.

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Old 11-08-2022, 04:30   #2
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Re: Diesel return line setup

What Beta is hoping to prevent here is the fuel running out of the engine by draining back into the tank via the return line.

The solution to this is
1. Tank higher than engine
2. Fuel return line submerged in the tank.
3. Fuel line that dips below bottom of tank.
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Old 11-08-2022, 04:59   #3
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Re: Diesel return line setup

We thought it was to avoid producing foam. What do we know Just never had a return line with a tube real close to the bottom of the tank. We always have a Carter electrical pump and TWO primary filters with a three way valve. Filter gauge shows you itís getting clogged, you just flip two levers and the engine keeps going. Bad weather always stirs up stuff in the tanks and itís takes time to physically change filters. Always happens at the worse times.
Our Yanmar final filter is on the engine higher than the injection pump but Iíll have to admit we didnít fit a return tube in the day tank. Love to hear from other members. Maybe itís a requirement for smaller diesels or small tanks. Iíll also re read our books on the subject.
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Old 11-08-2022, 05:08   #4
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Re: Diesel return line setup

The drain tube to the bottom of the tank is helpful in an extremely shallow wide tank that can easily foamÖ..
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Old 11-08-2022, 05:32   #5
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Re: Diesel return line setup

Quote:
Originally Posted by Sailmonkey View Post
What Beta is hoping to prevent here is the fuel running out of the engine by draining back into the tank via the return line.

The solution to this is
1. Tank higher than engine
2. Fuel return line submerged in the tank.
3. Fuel line that dips below bottom of tank.


I canít see this.

If the tank is lower than the engine then the fuel trying to drain back via the return line will be balanced by the fuel trying to be drawn upwards from the pickup line. The system will balance and no flow would occur.
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Old 11-08-2022, 05:35   #6
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Re: Diesel return line setup

Quote:
Originally Posted by Manateeman View Post
We thought it was to avoid producing foam. What do we know Just never had a return line with a tube real close to the bottom of the tank. We always have a Carter electrical pump and TWO primary filters with a three way valve. Filter gauge shows you itís getting clogged, you just flip two levers and the engine keeps going. Bad weather always stirs up stuff in the tanks and itís takes time to physically change filters. Always happens at the worse times.

Our Yanmar final filter is on the engine higher than the injection pump but Iíll have to admit we didnít fit a return tube in the day tank. Love to hear from other members. Maybe itís a requirement for smaller diesels or small tanks. Iíll also re read our books on the subject.

Mark


Not sure about the Yanmar but all the diesels Iíve met have a return line.

I believe they are part of the lubrication and cooling of the injector pump and as should return to the tank from which you are drawing fuel to keep the circulating fuel cool as possible.
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Old 11-08-2022, 05:40   #7
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Re: Diesel return line setup

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Originally Posted by GILow View Post
I canít see this.

If the tank is lower than the engine then the fuel trying to drain back via the return line will be balanced by the fuel trying to be drawn upwards from the pickup line. The system will balance and no flow would occur.


It can happen, but you almost need to plan for it with your return line routing. Ie, a nice uniform slope that allows air from the tank to ride on-top of the fuel from the engine inside of a small fuel hose.
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Old 11-08-2022, 05:49   #8
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Re: Diesel return line setup

And some only route the return back to the secondary filter or a tee in the supply line. Handy for one engine feeding off multiple tanks, no switching required and can save a lot of plumbing. A little harder to bleed off though.
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Old 11-08-2022, 05:53   #9
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Re: Diesel return line setup

Yes. Our Yanmar has a return fuel line. We just never fit a return TUBE into the tank so that it looks similar to the drawing posted at the beginning of the thread.
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Old 11-08-2022, 06:35   #10
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Re: Diesel return line setup

Most tanks Iíve seen donít have pipes to the bottom for the return line.
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Old 11-08-2022, 08:06   #11
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Re: Diesel return line setup

Quote:
Originally Posted by GILow View Post
I can’t see this.

If the tank is lower than the engine then the fuel trying to drain back via the return line will be balanced by the fuel trying to be drawn upwards from the pickup line. The system will balance and no flow would occur.
Well, the tank is vented to the atmosphere.

And if you plug the top of a drinking straw with your finger and lift it out of a glass the water will stay put, but if you sit there vibrating it for hours I'm pretty sure gravity will do its thing, right?

(but on the other hand, my return line to a tank well below the engine has no dip tube and the return line is above the tank the whole way, and I've never knowingly experienced 'drain down'. )
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Old 11-08-2022, 08:21   #12
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Re: Diesel return line setup

As Sailmonkey said in the first response; With a tank that is set lower than the engine, over time, gravity will allow the return line to completely dry out and allow air to back up into the injector return rail. Which can then allow air into the injectors. This causes starting 'gremlins'. The drop loop to prevent draining of the return line prevents this from happening.

It really does not matter if the return line drops onto the top of the fuel or extends to the bottom of the tank.
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Old 11-08-2022, 08:51   #13
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Re: Diesel return line setup

Drain down, drain out...whatever you wish to call it, not having a tube going to the bottom of your tank is going to leave the injectors dry ? And the illustration shows a wet loop ..donít know what to call it...in which the return line takes a U turn in addition to the in tank tube.
So if I donít have this arrangement, my injectors will be dry, start to rust, destroy themselves and Iíll have starting gremlins.
I just want to make sure Iím straight on the facts. Not being sarcastic. Iíll disconnect my fuel return line and see if it bleeds out.
Iíll also check to see whatís in the Yanmar installation book. Thatís if the manatees are not using it for a pizza bazooka target.
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Old 11-08-2022, 09:00   #14
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Re: Diesel return line setup

My diesel always returned to the top of the tank and dribbled in. Never was an issue. I suppose if you are running a 3000 HP diesel maybe it is , I dont know. But for an engine that burns less than a gallon an hour, the amount of return is very minimal...
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Old 11-08-2022, 10:37   #15
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Re: Diesel return line setup

IIRC I have never worked on a diesel mounted above the fuel source; I have always had a positive head on my fuel lines. This may be why I have never heard of "fuel drain down."

The engine I am working with now is an EMD645 20 cylinder, it puts out 3,600 horsepower and returns a significant amount of fuel. Our two smaller generators are run by 800 horsepower C-18 Caterpillars, and those also return a lot of fuel. In fact I can feel the fuel return line get warm when they are loaded and get hot to the touch when there are temperature issues. I suspect modern engines return more fuel for finer temperature controls (both for EPA and horsepower efficiency the thermal envelope really gets pushed a lot harder than the old days).

I say all of this to make relevant the importance of having a proper fuel return setup. For me it returns to the top of the day tank (fuel return lines are, in my experience, never plumbed to the bottom because you want to minimize return pressure - preventing return flow is bad for injectors and can shut down an engine) whereupon gravity takes over. Never heard about the drop tube to prevent diesel foaming but the logic makes a lot of sense for a smaller tank, even with baffles I could see fuel getting aerated.

I found this thread that might be useful:

https://forums.ybw.com/index.php?thr...n-line.237153/

My takeaway is that if your fuel tank is above the engine then don't worry about fuel drain down; it's impossible.. If the tank is below the engine then I actually really like the one comment from the posted link about having an upward loop on the return side that keeps the diesel right at the injector rail.

I would love to hear from a Beta engineer!
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