Anti-overflow valve causing fuel to leak in the bilges... ugh

Jul 6, 2013
51
Hunter 336 Société Nautique de Genève
Just took delivery of a Dufour. According to new EU environmental regulations, there is an anti-overflow valve on the fuel vent line. So when you fill the tank a little too full and the fuel expands because of warmer temperature, rather than dripping overboard via the vent line (a bad thing), it finds the least hermetic point downstream and forces fuel into the bilges through a poorly sealed access port or a poorly fitted fuel hose (a worse thing). If enough leaks, it will wind up overboard anyway, via the bilge pump.

We always try to avoid overfilling but it happens sometimes in spite of the best intentions.

Short of removing the anti-overflow valve, are there any other suggestions for avoiding diesel to leak below, or worse, to explode the fuel tank if it expands enough?
 
May 27, 2004
1,964
Hunter 30_74-83 Ponce Inlet FL
Yes, BUT!
There used to be a product sold that attached to the hull area of the vent via suction cups.
It was no more than a 10oz or so, clear plastic bottle (like many fuel supplements or other chemicals come packaged in) that had a hole in the side and two suction cups flanking the hole, mounted on a flange and glued to the bottle.
If you have the hull vent system, find a bottle, cut a 2 inch hole in the center of one side, hold it against the hull over the vent and imagine a flange with the suction cups holding it there.
If you have the internal system, attach a bottle without cutting the hole in the side.
Just run the vent hose into the neck of the bottle and secure it with a hose clamp or quick release. In either case, remember to empty the bottle back into the tank when refueling is complete.
You can make one as I had to do when someone stole mine at the fuel dock!
Sadly, they are no longer commercially available.
 
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Jul 6, 2013
51
Hunter 336 Société Nautique de Genève
Thank you. That’s interesting to address the problem of fuel overflowing through the vent line. My problem is that the obligatory anti-overflow valve doesn’t allow fuel through the vent line in the first place, forcing it to leak through the weakest link along its path to the tank, from the tank, or further downstream toward the engine.
 
May 17, 2004
5,028
Beneteau Oceanis 37 Havre de Grace
Not a great situation. Off-hand the only solutions I can think of are to remove/bypass the backflow valve or not fill the tank so high. Is the EU requirement that all boats built after a certain year must have the valve physically present, or is it just a requirement on the builder to include it? Also, where is the valve, just off the tank, or at the hull end of the vent? Placing it nearer the hull, and maybe adding a longer vent hose, might give some extra room for expansion before the valve kicks in.
 

SG

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Feb 11, 2017
1,670
J/Boat J/160 Annapolis
Seal the leaks? Is the problem accessibility? We have two tanks sealing plates for the ports on the top. One both: One pate is for access & the tank guage; and, the there other hast the ports in it for the various fill tubes, return lines, etc. Both occasionally need to be removed and rebedded. If you over fill the tank, you put pressure on these plates' seals -- but, even if you don't , when you're healing or in a rough seaway, you have fuel sloshing or sitting under there.

Sealing them involves having cleaning the old sealant off; and reapplying new. It's is more an art, then a science. When they're sealed, nothing comes out. When they're not, we have oil absorbing pads that let us know they are not perfect.
 

senang

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Oct 21, 2009
304
hunter 38 Monaco
Have a look at the Vetus fuel stop system. Fuel and foam coming up are collected send back to the tank. Installation is under deck, access to fuel filling and vent lines are needed.
 
Dec 8, 2017
25
Hunter 326 Dana Point
Why can't you just plumb a catch can into the vent line. It seems a simple solution but it must be wrong, because I can't find a mention of it as a solution anywhere on this forum. I'm new to owning a boat so I've apparently missed something. Air will still vent and any fuel that gets there goes into the can and you stop filling...
 
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senang

.
Oct 21, 2009
304
hunter 38 Monaco
I looked up fuel expansion tank in our friend ggl and found that this is often installed in cars. Filling up a car and then parking it in the hot sun to go shopping I can understand that fuel expansion is a bigger issue on cars then on boats. You can buy a tank and install it in the vent line above the tank level. When the fuel expands it has the space available before reaching the overflow level. No more fuel in the bilge!
 

SG

.
Feb 11, 2017
1,670
J/Boat J/160 Annapolis
I looked up fuel expansion tank in our friend ggl and found that this is often installed in cars. Filling up a car and then parking it in the hot sun to go shopping I can understand that fuel expansion is a bigger issue on cars then on boats. You can buy a tank and install it in the vent line above the tank level. When the fuel expands it has the space available before reaching the overflow level. No more fuel in the bilge!

These are supposed to be closed systems for purposes of the inside of the boat. The vents are to be located where they don't get sparks or flames anywhere close to them. You are not supposed to get any fuel in the bilge. If you have some, then something is wrong. If it's not a leak, then there is a problem with the "design" or installation.

The vent is to the outside, not inside of the hull. That's to deal with both heat, and positional issues. If the boat rolls, or whatever, the fuel isn't supposed to be in the boat. Further, fuel gases are NEVER supposed to be contained in the boat. No open fuel container or pan is acceptable. While gasoline out gases more and it's fumes are more flammable, diesel fuel is can catch fire too -- aside for the generally unacceptable odor and it's long-term health impact. These are supposed to be closed systems for purposes of the inside of the boat. The vents are to be located where they don't get sparks or flames anywhere close to them.

Gas has over a 10% higher expansion factor with temperature increase than diesel fuel -- but both expand. (Watch it wither jerry jugs and "cans" that sit in the heat.) For gasoline, a simple putting a can in the sun and having a 40 degree F rise, will add over a 2% to the volume of the fuel
  • Diesel fuel - 0.00083 per degree Celsius (0.00046 per degree Fahrenheit)
  • Gasoline - 0.00095 per degree Celsius (0.00053 per degree Fahrenheit)
 
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