How to connect a second fuel tank?

[cmedsailor]

I am thinking of adding a second fuel tank somewhere in the lazarette where I would simply transfer, when needed, fuel from that additional tank to the main fuel tank. As you can see from the photo my main fuel tank has simply the fuel supply pipe (after the fuel isolation valve) and the fuel return pipe (covered with some sort of silicone; was like that since I bought the boat and never touched it).
Do you think it would be possible to connect the pipe coming from the additional tank to either the place where the return pipe enters the main tank or probably a small distance before that? I mean to connect it to the return line with a Y or T connector? Would that affect the flow of the return fuel to the main tank?
Thanks

 

[rob2]

Unless you put a non-retrun valve in the transfer pipe, return fuel will be able to go to either tank, possibly undoing the work of transfer to the main tank. I would be inclined to look into fitting a totally separate point of entry for the transfer pipe into the main tank. Alternatively a stopcock on the transfer pipe would act in place of a non-return valve, but may be misunderstood by crew as to its function.

Rob.

 

[William_H]

Feeding from second tank

As said if you tee to the return pipe there may be a tendency for return fuel to run back to secondary tank if there is any resistance between the tee and the tank. Best bet I think is to fit another fuel feed in either to the tank or to the filler pipe. I would suggest you might find it easier to buy a little purpose built electric fuel pump. This will enable the secondary tank to be quite low in the ship. (Unless you can use gravity feed.) If you don't have a fuel level gauge for the main tank you should have an overflow pipe from main tank back to secondary tank in case you try to overfill the main. If this overflow pipe is large enough it could be used to fill the secondary tank after filling main.
With fuel return complications it can be complicated to feed from the alternative tank straight to the engine as you would have to switch return line as well. Although this could be valuable with second fuel filter in case of contamination of fuel. (bugs) good luck olewill

 

[rogerthebodger]

I have 3 separate tanks feeding my main engine and I made up a twin 4 way valve (1 for each tank and off) for feed and return

 

[cmedsailor]

Let me just add that my thoughts are to add a lever (most probably) valve to the secondary fuel pipe right after the secondary tank in the lazarette and then use gravity (hopefully) or an electric pump to transfer fuel to the main tank. So if any fuel from the return pipe follows that "secondary fuel pipe" it could only fill this pipe. However I could always also add a non-return valve to the secondary fuel pipe just before the connection with the return pipe. This will prevent completely any fuel flowing from return pipe to secondary tank.
My biggest concern though is whether, during transferring, any fuel flowing from secondary tank via the secondary fuel pipe could flow into the engine via the return pipe (probably not, probably stupid question as I am not a mechanic). Also keep in mind that transferring could be done with the engine working or not.
Thanks

 

[cmedsailor]

I would be inclined to look into fitting a totally separate point of entry for the transfer pipe into the main tank.
.

Actually this is the ideal solution. But how I am going to add this into such plastic tank? If I cut a whole on the top of the plastic most probably that little piece of plastic will fall into the tank. Then there is not any inspection hatch that I could probably open and use my hand to do any sort of work within the tank.
Any ideas?