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Old 06-02-2017, 12:07 PM   #1
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Do any diesel fuel tank systems direct vent back to the fuel fill?

All the new gasoline fuel fills direct the vent back to the fuel fill as a way of stopping fuel from going into the water.

Other thing, how about normally sealed fuel caps with vapor and pressure relief, similar to a car. The caps vent to the atmosphere on engine fuel demand and when the atmosphere pressure difference exceeds 1 PSI on pressure and less than .25 PSI on suction.
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Old 06-02-2017, 11:14 PM   #2
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My four diesel tanks don't. The vents are about two feet above the inlets. If tanks are being overfilled, the overflow comes out of the inlet. If the fuel return goes to the wrong tank and overfills, the overflow comes out of the vent. Any overflow runs down the deck and then drops overboard unless one has an absorbent towel to intercept.
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Old 06-03-2017, 06:26 AM   #3
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I watched a tv show where a diesel trawler was caught in a bad storm traversing the Gulf of Mexico. The engines kept stalling out due to water getting into the fuel. The guy would clean the filters, it would run for a while and quit again, and he was confounded about how water was getting in, they finally lost engines and could not restart and were rescued by the USCG and lost the large trawler, sunk into the sea. The trawler was new, so modern at that time from what I recall.

In the show it was determined that water was entering the fuel tank by way of the tank vent
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Old 06-03-2017, 07:14 AM   #4
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Greetings,
I think I read somewhere where some tank vents were located inside the gunwale thus directing vapors onto the deck rather than overboard. I suppose being diesel, explosion due to vapor accumulation and subsequent ignition would be minimal.

One of MY fears is fuel spewing out of the overflow when topping up our tanks. Inboard relocation of tank vents would allow containment of potential "spew" and subsequent clean up as well as prevent water ingress in heavy seas.
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Old 06-03-2017, 07:17 AM   #5
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I watched a tv show where a diesel trawler was caught in a bad storm traversing the Gulf of Mexico. The engines kept stalling out due to water getting into the fuel. The guy would clean the filters, it would run for a while and quit again, and he was confounded about how water was getting in, they finally lost engines and could not restart and were rescued by the USCG and lost the large trawler, sunk into the sea. The trawler was new, so modern at that time from what I recall.

In the show it was determined that water was entering the fuel tank by way of the tank vent
Ummm, sound familiar.
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Old 06-03-2017, 08:24 AM   #6
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Over half a century ago when I was learning about boating, vented tanks to outside the hull were just that, fuel spillers and water ingress points. About thirty years ago boats started coming out with vent lines plumbed inboard. Two of mine are, and two go outside to the stern.

The two outside vents on the stern tanks have a big easily visible clear loop from the lazarette. The loop traps fuel. Even in big stern seas the loop remains a fuel loop. Never seen any water. A few times in anticipation of heavy weather I duct tape the outside vents closed. A CG buddy says this is what they recommend, taping the vents in the event of a list due to grounding. I've seen it done twice on grounded vessels.
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Old 06-03-2017, 08:54 AM   #7
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Our vents have been annoying. One got plugged on a holiday (which had me upside down and sideways for a while to fix it after noticing one tank wasn't draining) and once while filling the tanks in -10C weather the vents were plugged...it took forever to sloooowly add fuel while it continually burped back.

There's got to be a better way...

Our lazarette (where the diesel tanks are) has two stainless steel louvered vents near the inboard gunwale on either side of the transom door to the swim step.

Couldn't the tank vent lines terminate inside the lazarette, up near the gunwale, on the inboard side of those louvered vents?

I could put insect screens under the louvered vents to keep bugs away, and the location should stop blowing snow and spray from blocking the vent hoses.

On the subject of burping/foaming fuel and having the vent line attached to the fill pipe: https://www.vetus.com/fuel-systems/s...-for-fuel.html
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Old 06-03-2017, 09:45 AM   #8
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Diesel vented fill. There is an optional spacer which gets the fill up off the deck. Found that in some of the molded filler deck recesses water could find its way through the cap even though there was a water trap in the vent.

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Old 06-03-2017, 10:58 AM   #9
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Greetings,
I think I read somewhere where some tank vents were located inside the gunwale thus directing vapors onto the deck rather than overboard. I suppose being diesel, explosion due to vapor accumulation and subsequent ignition would be minimal.

One of MY fears is fuel spewing out of the overflow when topping up our tanks. Inboard relocation of tank vents would allow containment of potential "spew" and subsequent clean up as well as prevent water ingress in heavy seas.
My friends lobster boat is plumbed exactly like that for those reasons.
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Old 06-03-2017, 11:11 AM   #10
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My vent goes up the side of the cabin to the top deck, where it ends in a 180 degree loop. one each side of the boat. Any fuel vent in the side of the hull is risky.
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Old 06-03-2017, 11:40 AM   #11
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I always has concern while fueling. I do not not the exact tank capacity (from my observation it should be around 250L per tank) so I am always nervous while refueling. I like the device that was posted on another thread with a whistle on the vent line but to install this will be a real pain at this time because of access. It would be nice to have something that could connect to the vent when you refuel that would collect any spill, something like a threaded vent where it would be possible to screw on a box to get any spill and ensure nothing goes overboard when refueling.

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Old 06-03-2017, 01:04 PM   #12
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Hopcar had a fueling device, try searching.
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Old 06-03-2017, 07:05 PM   #13
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Our vents are in the cockpit space so any expelled fuel at least has a chance of being caught before going overboard.

I think the key to protecting a vent from water ingress is to have the vent hose route up as high as possible - higher than you think the water will ever get - then come back down and connect to the vent. Then even if the vent becomes completely submerged in water, as long as the water level doesn't go above the loop, no water will get into the tank, and the water will self-drain out of the vent.
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Old 06-03-2017, 07:10 PM   #14
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What are you supposed to use for the vent line itself? The PO of our boat used water line which eventually folded over and pinched where it does the big bend at its highest point.
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Old 06-03-2017, 08:17 PM   #15
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My vents are in the main cabin walls and the vent exits about 6' above the deck. When the tanks get near full, all the air is going out the vents, allowing good control at the deck fill if I want the tanks absolutely full. Commercial fuel docks often have an extended nozzle that releases the fuel about 18" below the deck fill (if you have straight pipes). All the turbulence is well below the deck fill.
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Old 06-03-2017, 10:33 PM   #16
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What are you supposed to use for the vent line itself? The PO of our boat used water line which eventually folded over and pinched where it does the big bend at its highest point.
Mine are all marine fuel hose. 3/4" I think.
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Old 06-03-2017, 11:16 PM   #17
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Use fittings to make that loop,, not hose. Tie or secure the hose to the hull so it does not try twist the vent.
A ply pad glued to the hull and a small part eye would be secure.
The vents could be moved to the inwale as you asked before.
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Old 06-04-2017, 05:28 AM   #18
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Have 2 vents per tank that are mounted on the bulkhead next to the fill pipe. Each tank vent has a Parker / Racor vapor fuel separator to prevent fuel spills.

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With the vent near the filler, it's easier to hear thr sound change as the tank nears full.

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Old 06-04-2017, 09:04 AM   #19
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My tank fills are right on the top of the tanks. Tractor trailer fill caps. Vents not in play when fueling, tank vents then through the big fill opening. Vents go to a catch trap in engine room and are not exposed to sea. I know this is against the rules, but I think the risk is very low.
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Old 06-06-2017, 05:04 AM   #20
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We took out the deck fitting and cut a 6inch hole where it was located
We installed a bronze flush cover , but plastic would work as well.

The fill hose was cut back a couple of inches a std plumbing nipple and cap were installed, along with a ground wire from the nipple to the fuel tank.

The cap has a 1/8 hole for venting drilled in its side.

DONE.

The DD 6-71 draws up to 20 GPH , but returns most (17GPH) so a 1/8 vent is enough not to collapse a tank while drawing 3 GPH. At Flank 12GPH , still no problems.

With no overboard vent , overfilling would not cause the Sheen Police to react.

With plastic parts this is a $10.00 fix .
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