Twin Fuel Tanks

[johnneale]

I have twin tanks with a changeover tap to switch between them prior to the primary filter. However the fuel return from the engine is routed only to the Stbd tank. That is fine if only drawing fuel from that tank, but if I draw fuel from the Port tank then that will empty quickly whilst in danger of overflowing the Stbd tank.

I would prefer to keep the tanks independant, and could route the fuel return to both tanks, but would I face the same danger of emptying one tank and overfilling the other ?

The last resort would be to draw fuel from both tanks and return to both tanks, but am I still in danger of overfilling one and depleting the other?

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[brianrunyard]

Just a thought, you could put a changeover valve in the return, so you return to the same tank that you're taking fuel from.
You could also put a connection between the two tanks near the tops so if you do start to overfill one tank it can overflow to the other tank.

<hr width=100% size=1>Brian
http://homepage.ntlworld.com/brunyard

 

[MarkV]

Don't know anything about engines, fuel lines or anything, but couldn't the return line feed back into the supply line between the changeover valve and the filter? alternatly couldn't you add a changeover valve to the return and feed it to the tank being used? If I'm takling rubish I'm sure someone will point it out.

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[Nauti Fox]

Think the easy way would be a balance pipe between the tanks.The only drawback I can see is they're no longer independant if you get contamination,although its filtered diesel returning so should'nt be a problem.
Ours runs a balance pipe that has a shut off valve as the genny returns to one tank only.

<hr width=100% size=1>No dear,the water goes in the other one.

 

[johnneale]

Gee - I like that to put return line after changeover tap - could go into secondary input for primary fuel filter.

Cant put changeover tap in return line as return fuel spigot on tank requires very narrow pipe which would'nt fit new tap. Also I don;t want to go scurring under the floorboards to switch over.

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[pvb]

Recycling the fuel return...

Not sure it's a good idea to recycle the fuel return directly back into the supply pipe. Returned fuel has been heated slightly. If you keep letting it circulate in this way, it might get too hot. I'm sure one of our diesel experts could advise on this. Probably safer to let it go back into the tank and add a balance pipe instead.

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[Nauti Fox]

Re: Recycling the fuel return...

Yup, agree with you there.When its been through the fuel pump a few times it will be pretty hot.

<hr width=100% size=1>No dear,the water goes in the other one.

 

[Paulka]

Both my Volvo MD2B, then MD11C have the return connected to the filter.
This is (was?) how the engines came from the manufacturer.

This way, the return "doesn't exist", or at least has not to be lead to any tank.

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[Piers]

It is a sad fact that some boatbuilders, to save costs, only return excess fuel to one tank, more than likely relying on the fact the tanks can be manifolded to keep them balanced.

First, it is good practice NOT to have them manifolded, for balance reasons when stationary, as well as potential contamination issues.

Second, it is certainly NOT recommended to feed the spilled fuel back into the supply line.

Third, I would re-arrange the return lines from the engines so each fed to its respective tank.

Once this is done, you just need to be aware that the exception would be that when running from one tank only, you would start to have an imbalance situation developing, although this is perthaps the time when manifolding the tanks might be prudent.

<hr width=100% size=1>Piers du Pré
http://www.dupre.co.uk

 

[pappaecho]

My brothers Kingfisher 30 has exactly the same problem 2 x 40 gallons tanks in each of the bilge keels. Twin changeover valves allow to draw from one and return to the same or opposite tank dependant on their relative gallonage. The beauty is that you can draw from one and return to the other and hence balance the boat. His system is over 30 years old

<hr width=100% size=1>Def: Yachting - a way of spending the kids inheritance

 

[TheoSr]

Returning into the supply line has been known to cause problems as it may bring air into the fuel. Will not stop the engine, but will cause difficult starting.


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[brianrunyard]

Agree with what you say but, reading the original question it implies that it's a single engine installation with twin tanks. Therefore I stand by what I said, "return to the tank you're taking fuel from".

<hr width=100% size=1>Brian
http://homepage.ntlworld.com/brunyard

 

[Piers]

Aha - one engine. Should have read more carefully. In which case I agree with you. Have a switch over to direct the return to the tank you are drawing from, and remember to manage the fuel system as you go.

<hr width=100% size=1>Piers du Pré
http://www.dupre.co.uk

 

[AndrewB]

Agree with others that you need a changeover switch in the fuel return line to allow fuel to be sent to whichever tank you are running from. This is the normal arrangement, your present one sounds like the result of a bodge. Some good arguments have been put for this already, but for me the key one is to be able to completely isolate one tank in the event of contamination.

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[johnneale]

Thanks to all - & wont bother routing back thru primary filter - (heat & unable to get air out of system etc)

Leaves me with either another changeover tap (under floorboards) to route return to specific tank - difficult as problem there with pipe sizes,

or go for a balance pipe between both tanks

New question. if return is tee-ed to both tanks, and say fuel is drawn from tank A,
would very slight vacuum in tank A draw return to this tank rather than than both/either ?



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[tugboat]

Hi John. If the options you have been offered so far present difficulties you don't fancy dealing with, there is another way, if you have space. That is to fit a small daytank which you feed the engine from and the excess fuel returns to. This tank would be topped up from your main tanks with a manual or electric pump. I'm familiar with the Husky and you may have room in a cockpit locker(?) for one of those translucent tanks that are easy to monitor the level. Looking at your bio suggests you do a lot of motoring and the added capacity could be useful too. It strikes me that the pipework might be simpler than having to rip out your present tanks to fit a balance pipe. My own boat has a daytank system and it works well. Rgds,TB.

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[Nauti Fox]

No John,there is no vacuum in the tank because the fuel tanks have vents in them to allow air in as you use the fuel,also with just a Tee the fuel will probably return to whichever route has the least resistance.

<hr width=100% size=1>No dear,the water goes in the other one.

 

[pvb]

Would your simplest solution be....

Would your simplest solution be to replace your existing changeover valve with a T-port valve? This type of valve has 3 connections (like your existing changeover valve), but can be set so that either 2 or 3 ports are open at the same time. So, if you set it so that all 3 ports are open, it automatically forms a balance pipe connection between the tanks. It'd be easy to install, no additional pipework, no additional tank connections. You'd lose the ability to isolate one tank permanently (but then this would also be the case with a balance pipe and the return pipe only being to one tank). If you add Soltron whenever you fill up with fuel, there shouldn't be any fuel problems anyway. You can get T-port valves in various sizes from <A target="_blank" HREF=http://www.asap-supplies.com>ASAP Supplies</A>.

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