Help required re fuel tank breather pipes

[Becky]

Well, we have fitted a new tank, 50% capacity of the main one, and we plan to connect it such that the return fuel from the engine will go to the new tank and when this is full, will bleed off to the main tank from a T-piece in the bottom of the breather pipe. It will also have a direct connection to the engine feed pipe, such that, theoretically, we will always have clean fuel in a full reserve tank.

Which means that the breather will have fuel in it continuously.

What material would be most appropriate. Bearing in mind that fuel pipe itself is too narrow a bore as we will be able to fill the new tank from a deck filler as well?

 

[andyball]

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fuel pipe itself is too narrow a bore

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not sure what you mean there - hose suitable for diesel fuel can be had in lotsa sizes. Vetus ( Vitesse marine in Fareham ) or the likes of Hyphose or any 1/2way decent marine engineers should be able to supply fuel-suitable hose a wide range of sizes.

 

[Becky]

Thank you. Vetus is only 10 mins from my home, well Vitesse marine is, & they sell Vetus products.

The reason for my query is that we have a sight tube on the main tank, and were advised that not just ANY pipe would be suitable, as diesel can disolve/destroy the wrong type of pipe.

Maybe I have been ill-advised on this matter?

 

[Malish]

I think the issue wih your sight pipe is obtaining a see-through material which is resistant to diesel for long periods. Some transparent plastics (especially the cheaper ones) are not good at resisting diesel. On the other hand pukka fuel pipe, which is usually opaque, should be fine for your breather application.

 

[andyball]

nooo, true that some hose isn't good with diesel - eg the builders of some boats ( ha!, Mine ) use clear reinforced hose for fillers/balance pipes etc, which over time goes hard & can leak where it's clamped; quite apart from it being way less resistant to heat/fire.

Just get hose suitable for diesel, in the size you need.

 

[sarabande]

Becky - should a breather pipe have fuel in it anyway ? The purpose is to let air in and out of the tank as you fill or empty it. If you have fuel in the pipe it might be forced up and out the end of the breather.

 

[Becky]

'' Becky - should a breather pipe have fuel in it anyway ?''

This is the whole point. We are using the returned fuel from the engine to pass through the extra tank so that we will always have spare fuel, which has been through the fuel filters, so would presumably be quite clean.

But... we don't know at what pressure or pace the returned fuel comes in at, so that when the extra tank is full, and we bleed off the excess to the main tank, how far up the breather pipe the fuel will rise. In other words a clear pipe would be preferable.

This way of connecting the spare tank into the fuel/engine system seemed a very good idea, but I don't want to see fuel spurting from the spare tank breather while we are motoring. Or the spare tank being over-pressurised when it is full. We had enough of that sort of thing with the water tanks.

I hasten to make clear that the breather will be a high as we can get it.
So, what clear fuel pipe is there? Or should we just put in 15mm standard rubber fuel pipe and all will be well /forums/images/graemlins/confused.gif /forums/images/graemlins/confused.gif

 

[rhumlady]

It's not a breather pipe it's a excess fuel return pipe which goes from the Injectors back to the tank. the Breather pipe goes from the tank to a vent up on deck somewhere. Mine is next to the fuel inlet at the transom and is where the foam comes out just before the tank is full!!

 

[Stemar]

Igf I've understood correctly, the only supply to your new tank will be the return from the engine. I can see no good reason for this to be any bigger than your current return pipe, maybe 10mm internal diameter. This can go into the top of the tank. When the tank fills up, you want the overflow to go back into the main tank. If I was doing this, I'd want this pipe to be bigger than than the first one, maybe 12mm ID to be sure that you wont have any problems with pressure buildup. Both of these pipes can go into the top of you new tank, though it wouldn't hurt to have the return from the engine go in at the top and down to the bottom of the tank, while the overflow to the main tank should be from the top so it only comes into play when the tank's full.

I've seen setups like this where the day tank is higher than the engine, so fuel is gravity fed, which, theoretically, at least, it more reliable as a slight leak won't let air into the system.

I'd quite like to do the same thing, but I've no reoom for the extra tank, so I got round the sinking feeling that comes from a blocked filter just when you need the engine the most by putting in two filters in parallel so I run on one anf if it blocks, it takes a few seconds to switch fom one to the other. I also use spin-on filters. They're twice the price, but I've got a chance of changing them at sea with the boat bouncing around, which I REALLY wouldn't fancy with a CAV filter.

 

[boatmike]

Becky.
The plastic pipe sold in chandlers is not a preferred solution for three reasons.
1. It gets brittle over time and can crack
2. Some types go brown very quickly and for a sight tube are not too good.
3. It's a serious fire risk.
You can use it but get the reinforced variety and make sure the spec says "suitable for diesel" and inspect it regularly.
Can I also say that the return from the diesel injector line should always be returned to the tank that the fuel is fed from to avoid the possibility of a blockage or airlock causing one tank to empty and the other overflow. A far better arrangement would be to leave the existing tank as is and fit the "reserve" tank with a feed to the existing.
3 ways of doing that.
1. Existing tank and new tank at same height (bearing in mind the heeling effect on "half a boat" /forums/images/graemlins/smile.gif) Where the two tanks can be joined with a simple feed pipe near the bottom of both. This will act effectively as one tank but both need breathers with the breather on the one with a filler being not so high as the other when heeled (and when not) to avoid spillage.

2. Have a "bulk" tank and "day" tank where the feed and return are from the day tank to and from the engine and the bulk tank feeds it. If the bulk tank is lower down (best IMHO) you need a simple pump to feed the day tank which can either be automatic or manual.

or 3. Bulk tank higher than day tank with gravity feed and a simple isolating valve to fill.

All depends on where you put em and how you want it to work but the diesel return should ALWAYS go to the same tank as the diesel is drawn from.

 

[BSSOffice]

Suitable hose may also be marked as complying with BS EN 7840 which has 2m 30s fire resistance and certain permiability characteristics that make it more suitable for diesel in a marine installation.
There are many products out there and quite an number of suppliers including local chandleries, engne specialists and mail order. Try searching on '7840 hose'. You should find somebody who can offer something from stock.
Cheers
Rob@BSS Office