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Old 07-08-2012, 20:42   #1
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Electric Pump in Fuel Return Line

I am rebuilding the fuel system on Banjo. There are 3 tanks, one of which is above the engine. Under the current setup this o/head tank is mainly used to gravity feed a small auxiliary engine. In an emergency, the o/head tank can be switched to gravity feed the main engine, but the fuel return from the main engine only goes to the main tank below the engine.

I want to be able to switch the fuel return to go to the o/head tank when that is being used to feed the main engine. The issue is lifting the returned fuel up to the o/head tank. To achieve this I propose to put an electric pump in the fuel return line from the main engine to the o/head tank. My concern is that pump would be handling a very small amount of fuel, and would be running continiously, trying to pump nothing, against near zero pressure. Does anyone have any experience with this? There must be many boats with o/head tanks, facing this issue?

Any thoughts appreciated,
Lee
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Old 07-08-2012, 21:11   #2
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Re: Electric pump in fuel return line

Lee,
I cannot add any comment if it is Ok to add a fuel pump in the return line or not.

But would it not be an option to have a lift pump setup from the main tank to the o/head tank? You could lift the returned fuel from time to time and it may add a safety feature as well as you could feed the gravity tank....
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Old 07-08-2012, 21:23   #3
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Re: Electric pump in fuel return line

What kind of boat and where is the overhead tank located?

Unless your overhead tank is very high above the engine just add a valve to direct the return line back to the tank you are feeding from.
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Old 07-08-2012, 21:33   #4
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Re: Electric pump in fuel return line

I would add a pump to fill the overhead tank and use it as a day tank, let the return go anywhere it go's!! and fill the day tank as needed or plum up a manifold to fill and return as you might wish ! It would have the added feature of keepin your fuel cleaner if ya add a good filter to the pump set up ! And I like the gravity feed to the engine, always good to go even if your engine pump is bad!! just my 2 cents
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Old 07-08-2012, 22:01   #5
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Re: Electric pump in fuel return line

What engine is this? Some have a return from both the injection pump and the injectors. I suspect the pressure that will build in the line would be sufficient to lift it a reasonable height to the header tank.

I would not install the complexity of an electric fuel pump unless this was some sort of custom high performance engine of some kind that would justify it.

I guess I am curious why you are concerned about the fuel returning to a main tank. Overflowing the tank?

To keep things simple it would be nice to get a single lever double valve that switches the supply and return with one handle.

Tank Selector Valves || Preferred Utilities || Fuel Oil Handling
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Old 09-08-2012, 00:31   #6
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Re: Electric pump in fuel return line

Thanks for the replies. First, a little more about my setup. The boat is a Swanson yacht, with a Kubota based main engine, consuming about 3.2 litres per hour under optimum conditions, possibly 6-10 litres under wide open throttle. I haven't been able to get any specs on fuel return, but think it would be about 3 litres per hour. The engine is new, recently installed it myself.

The head from the fuel return on the engine to the o/head tank (built into a cockpit seat) is about 1.7 metres. The pressure coming out of the fuel return is near enough zilch. I have a mate Kev who is a injector/pump specialist of some 35 years experience, and he advises strongly against simply routing the fuel return to the o/head tank. He says the pressure build up in the return line would be enough to cause hydraulic lockup at the injectors (his words), resulting in the engine stopping.

The option of feeding off the o/head tank, running the return to the main tank, and periodically transferring fuel to the o/head tank is what I have at the moment, and I regard it as unsatisfactory, and bad practice. Everything I know and have read about fuel systems emphasises the importance of maintaining the integrity and separation of tanks, to avoid cross contamination and overfilling.

In my case I am particularily concerned about contamination. I have experienced contamination of the main tank, and on switching to the o/head tank, having the return go back to the contaminated main is not good.

The fuel return on my auxiliary, a single cylinder Yanmar ts60 feeding off the o/head tank, goes into the inlet of its primary fuel filter. That works ok, but the Yanmar only consumes 0.5 litres per hour, and the return would be miniscule. Stuff I have read on the web indicates such an arrangement leads to problems with larger engines. My mate Kev doesn't know, but instinctively doesn't like it.

Kev thinks putting an electric pump in the fuel return line, carrying a few spare pumps in case of pump failure, is the way to go. At the moment, thats what I am going to do. My purpose in posting was to find out any experiences here.

Thanks to "ex-calif" for the link to the dual valve, I didn't know such a thing existed. The one you have linked, while ideal in principle to my setup, is too large, but I am now googling for something similar and smaller.

Lee
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Old 10-08-2012, 06:29   #7
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Re: Electric pump in fuel return line

how about letting the overflow oil output from the engine go into a downstream fuel can.
Put a level sensor in the fuel can which drives a pump
level up = pump on
level down = pump off
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Old 10-08-2012, 07:34   #8
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Re: Electric pump in fuel return line

should be lots of fuel pressure in the return line to lift the fuel quite a few feet...
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Old 10-08-2012, 08:47   #9
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Re: Electric pump in fuel return line

Quote:
Originally Posted by rtbates View Post
should be lots of fuel pressure in the return line to lift the fuel quite a few feet...
yes sounds odd and OP says

Quote:
The pressure coming out of the fuel return is near enough zilch. I have a mate Kev who is a injector/pump specialist of some 35 years experience, and he advises strongly against simply routing the fuel return to the o/head tank. He says the pressure build up in the return line would be enough to cause hydraulic lockup at the injectors (his words), resulting in the engine stopping.
I always thought the return flow was a significant amount. This engine design is different?
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Old 10-08-2012, 08:51   #10
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Re: Electric pump in fuel return line

A discussion on blocked fuel flow return
diagram check #14 for a blockage
Oil & Fuel Fuel flow problem?

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Old 12-08-2012, 16:56   #11
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Re: Electric Pump in Fuel Return Line

As Ex Caif,suggested ,I,have the same arrangement and use the valve mentioned,My high tank is about 2 ft higher than the return line at the engin,work's fine with no pump.
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