Fuel tank overfill warning

[NormanS]

I am interested in a practical answer from those of you who advocate extending the breather to above the filler, which in my case (and many others?) is at deck level.
Where do you terminate it?

Well, my boat is a deck saloon, so it's easy to have them terminating well up on the side of the "house". With a lower coachroof, maybe on the aft bulkhead of the cabin. The one who has the breather on the transom presumably has a tank well aft, could maybe have the breather led up beside a taffrail stanchion. Wherever it is, it has to be beyond the reach of the sea, and have a down-facing opening, so that the rain can't get in.

 

[robertager1962]

Before doing all that work I would recommend doing a pressure test. Block all fuel pipes/breather except one that you can use to fit a pressure gauge and a tire valve then use a bike pump to apply 15psi and listen for the leak. I made up this arrangement recently to test my cooling system.

Www.solocoastalsailing.co.uk

Thanks.so much for a very simple and practical idea. I am not sure why it had never occurred to me. This is now going to be my first job tomorrow and hope I can get to the bottom of it. I really appreciate you responding.
Read more at http://www.ybw.com/forums/showthread.php?492351-Fuel-tank-overfill-warning/page3#9VSLdI6vzYE0Xi2P.99

 

[robertager1962]

If you have a leak, the answer is to sort it out, not paper over the cracks by some other method.

Sigh?!

 

[Quandary]

The breather usually won't be above deck level; it's sufficient for it to be close below deck level. It will indicate when the filler pipe is full. A breather above deck level is almost certain to discharge some diesel on to the deck, which is to be avoided.

I do know that, I was investigating Norman S assertion that I was out of my mind!
Of course he is right, but there are more obvious symptoms than the position of the tank breather?

 

[Deleted member 36384]

I am interest ..... Where do you terminate it?

On my own boat the tank breather is in the cockpit coaming, deck side, same side as the filler, with the filler in the deck, I honestly thought this was normal until this thread. In my case it is about 12" above the deck level filler.

 

[Normalfornorfolk]

Before doing all that work I would recommend doing a pressure test. Block all fuel pipes/breather except one that you can use to fit a pressure gauge and a tire valve then use a bike pump to apply 15psi and listen for the leak. I made up this arrangement recently to test my cooling system.

A cooling system is designed to be modestly pressurised and built of cast iron & alloy and thick reinforced rubber hoses. I am not at all sure that fuel tanks, especially thin sheet-metal metal ones are going to take 15psi (1 bar) without doing a blowfish impression or splitting a weld. After all, you can easily collapse a steel oil drum which is both much stronger in shape and material than a thin rectangular ss diesel tank by boiling water in it and waiting for it to condense. This at rather less than 15psi, 1 bar (cos you won't manage to displace all the air inside.)

I'd have a care with this plan, the method is perfectly sound but I fear for the angst and expense if the walls aren't up to bearing the pressure. Your fuel tank ain't gonna like that I reckon.

(eg a rectangular tank 30 x 40 x 50 cm capacity 60 litres so representative for a small yacht. The larger sides at 40 x 50 = .2sqm. The theoretical pressure exerted on that area at 1bar is 2 Tonnes!) unless I've got my maths wrong.

nb airliners are only pressurised to a fraction of this.

 

[lw395]

A cooling system is designed to be modestly pressurised and built of cast iron & alloy and thick reinforced rubber hoses. I am not at all sure that fuel tanks, especially thin sheet-metal metal ones are going to take 15psi (1 bar) without doing a blowfish impression or splitting a weld. After all, you can easily collapse a steel oil drum which is both much stronger in shape and material than a thin rectangular ss diesel tank by boiling water in it and waiting for it to condense. This at rather less than 15psi, 1 bar (cos you won't manage to displace all the air inside.)

I'd have a care with this plan, the method is perfectly sound but I fear for the angst and expense if the walls aren't up to bearing the pressure. Your fuel tank ain't gonna like that I reckon.

(eg a rectangular tank 30 x 40 x 50 cm capacity 60 litres so representative for a small yacht. The larger sides at 40 x 50 = .2sqm. The theoretical pressure exerted on that area at 1bar is 2 Tonnes!) unless I've got my maths wrong.

nb airliners are only pressurised to a fraction of this.

Indeed, you don't need anything like 15psi.
When I test my sailing dinghy buoyancy, a pressure of about 2 inches of water (about 0.1 psi?)
is enough for the fairy liquid solution to bubble around the leaky fittings.
That still adds up to a lot of force trying to lift the deck off the hull though!

 

[NormanS]

A dinghy pump will give you about 1.5 lbs/sq". Plenty for a leak test.

 

[skyflyer]

My fuel tank has a manufacturers label on it stating that it was tested to 3 p.s.i. This equivalent to approximately 8ft pressure head of diesel fuel.

I cant see any issue with having a breather outlet below the filler inlet. Obviously it has to above the tank level. What is the issue. I'd rather see it on the transom than anywhere that an overflow will spill onto the deck.

 

[GeorgeLlewellin]

Recommend a method of preventing overfill of fuel.

No one seems to have suggested the Vetus Fuel Splash-Stop, I fitted one eight years ago, it has worked very well. I still have to listen carefully but when the fuel suddenly comes rushing up the filler pipe, it stops just before deck level. Providing you stop adding more, there is little or not overfill.

It is not cheap, but it is effective, see here
https://www.mailspeedmarine.com/fuel-splash-stop-38mm-fillercap.html £73.30

Hope this helps. George

 

[NormanS]

My fuel tank has a manufacturers label on it stating that it was tested to 3 p.s.i. This equivalent to approximately 8ft pressure head of diesel fuel.

I cant see any issue with having a breather outlet below the filler inlet. Obviously it has to above the tank level. What is the issue. I'd rather see it on the transom than anywhere that an overflow will spill onto the deck.

The issue might (literally) be at the transom!
Unless you have a foolproof method of stopping filling the tank before it's full, you could keep on putting fuel in, and it will keep on overflowing out at the transom. At least if some fuel overflows onto the deck, it's easy to mop it up. If it comes out of your transom, it's right into the sea. Surely you don't want that to happen?

 

[skyflyer]

The issue might (literally) be at the transom!
Unless you have a foolproof method of stopping filling the tank before it's full, you could keep on putting fuel in, and it will keep on overflowing out at the transom. At least if some fuel overflows onto the deck, it's easy to mop it up. If it comes out of your transom, it's right into the sea. Surely you don't want that to happen?

Why would you keep putting fuel in if it was coming out the overflow? That was my initial thought but I've just realised the answer:- "because the filler point is nowhere near the transom". Apologies, I ws thinking of my own boat where the filler and breather (on the transom) are so close that you hear the fuel starting to rush uptake breather. (I still sometimes have a bit of overflow, though, which is not good). Environmental rather than safety issue unless you pump gallons and gallons into the sea, of course!

 

[Lodesman77]

On my own boat the tank breather is in the cockpit coaming, deck side, same side as the filler, with the filler in the deck, I honestly thought this was normal until this thread. In my case it is about 12" above the deck level filler.

+1