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Sealed fuel systems and vacuum...

Eric.C

Contributing Member
Just a thought, and curious if anybody has considered this before.

These days, cars all have evaporative emissions controls (aka "evap" systems). What this does is draw a vacuum on the fuel tank, then the ECM/PCM monitors the vacuum. If the vacuum decreases faster than a pre-determined rate, the check engine light will illuminate. This is to keep moisture (etc) out, and gasoline fumes in.

My thoughts... has anybody tried a sealed fuel system on a boat? It would be fairly easy to do, I would imagine. The engine provides the vacuum, a regulator could limit the vacuum (say 1-2 inHg), and you would drastically decrease the likelihood of water ever getting into the fuel. Be it splashing into vents on a rough trip, or condensation buiding inside the tank.

Any thoughts on this? :cool:
 
I wouldn't even consider it. The safety issues that would exist with an EVAP failure are numerous and serious. The cannisters (are they still using them on the newest models) can hold enough vapor to destroy any gasoline engine powered hull.

The potential for contaminated fuel, via the vent lines, isn't eliminated using an EVAP system, but it would be minimized. If the venting functioning failed, the potential damage to the fuel tank could be VERY expensive - Cut the hull to replace the tank!

Also, an EVAP system really wouldn't do much for the "condensation problem" alleged to plague the marine world. If you pull fuel out of a tank, it has to be replaced by (usually) warm moist air.

Finally, adding an EVAP system would likely increase the risk of water entering the fuel system - All those pieces provide opportunities for new entry paths and it doesn't do anything to eliminate the common known existng leak paths.
 
Thanks for the reply Mark.

Yes, charcoal canisters are still used, and I see what you mean about the fumes they hold. That part I can understand, but would a canister be required in a marine application? As boats sit now, gasoline fumes can freely enter the atmosphere anyway. Boats do not have ORVR, or any type of vapor control, so you shouldn't need to add a canister. The canister on a car is entirely for reducing emissions (polution reasons). If we can freely vent vapors now, I would think we could skip the canister/vapor-bomb.

Granted additional parts will create additional "links in the chain" (don't get me started with these new cars that practically wipe your arse, hehe), but what I am proposing would be a fairly simple system. Vacuum pulled on the tank from the engine, controlled by a regulator, and use a vacuum relief valve on the traditional vent hose as a back-up to vent the tank if needed. Relief valves are the epitome of 'safety', so I would think using one as a back-up should eliminate any chance of damaging a tank (though my thoughts do not always concur with reality).

Vacuum tube from engine to tank with a 1-2inHg vacuum regulator, 1-2inHg regulator on a filtered (seperator?) vent for normal venting, and have a back-up relief valve at 3-4inHg for redundancy/safety on the traditional vent hose.

No? Bad idea?

I am not planning on running out to the hardware store to mock this up, but I have definitely had returning thoughts on the idea. Wanted to bounce it by some marine experience. :)
 
I think it is a good idea to add a charcoal cannister. I have read where the EPA is saying that new boat tanks and fuel systems must have evaporative emissions control real soon. "diurnal fuel tank vapor emissions" control means possibly a charcoal cannister to absorb vapors.

http://www.epa.gov/otaq/regs/nonroad/marinesi-equipld/420f08013.htm#4
We are also adopting new standards to control evaporative emissions for all vessels using marine spark-ignition engines. The new standards include requirements to control fuel tank permeation, fuel line permeation, and diurnal fuel tank vapor emissions, including provisions to ensure that refueling emissions do not increase.
 
I also do one thing with my boat. I have a nice bronze threaded pipe with a bronze screw on metal cap for the fuel fill, none of that almost flush plastic deck fitting with rubber seal that can let water into the tank. My fuel vents are long copper pipes which run at a downward angle and where they exit the hull have a clamshell vent cover. I usually take a wad of paper towel and stuff it in that vent. I do this because I think it helps slow down the air flow in and out of the tanks which I think will help keep the gas fresher. I only keep that in there when the boat is sitting.
that wad does allow a certain amount of air movement so the tank is not going to "oil can", etc...
Some people cant do that because there vents are those round knobby things.

I have thought about adding a large metal bottle device on top of the tank vent inside the boat to absorb overfilling the tank issues. right now if you overfilled the tank, the fuel would gush out the vent then gush out the fill pipe. If you had a bottle tank on top of the vent, then before the vent overflowed, you would get it gurgling out the fill pipe.
It is just too easy for someone to make a mistake filling the tanks and then have an incident.
And I have read about people filling up and those exterior tank vents dribbling fuel into the water.

All I can do really is use a calibrated dip stick and figure out how much fuel I can safely add.
 
Racor has had a trap for the vent line for years - pricey but works well (all recommendations were to get the 'bigger' size, not the fussy little one).

So far, the EPA has been sane about grandfathering the older stuff so, for us older readers, it shouldn't have any impact.

Though I haven't messed with the 'newer' stuff, on what I do have (auto-wise) the cannister works as the fume trap in the 'vent' system. The valving closes/opens the ports when the ecu determines these actions are needed based on the drive cycle. The evap monitor just determines when there is a void or blockage in the system based on the vacuum monitoring.

If your intent would be to keep the contaminents out, I'd be more incline to pressurize the system. A vacuum would exacerbate any leak path (a common one is a deteriorated o-ring at the fill cap) that will (given enough use/time) develop.

The idea may have some merit but violates one of my fundamental tenant - the KISS principle. I'll keep mine in its current configuration.
 
.........Some people cant do that because there vents are those round knobby things.

I have thought about adding a large metal bottle device on top of the tank vent inside the boat to absorb overfilling the tank issues. right now if you overfilled the tank, the fuel would gush out the vent then gush out the fill pipe. If you had a bottle tank on top of the vent, then before the vent overflowed, you would get it gurgling out the fill pipe.
It is just too easy for someone to make a mistake filling the tanks and then have an incident.
And I have read about people filling up and those exterior tank vents dribbling fuel into the water.

All I can do really is use a calibrated dip stick and figure out how much fuel I can safely add.

I guess one has to consider what type of vessel they have and how to prevent spills.

I have the "knobby" thing, :D(air vent),:D out the back on a fibreglass transom for each tank and what I use when filling the tanks is the "no-spill" bottle. ..plastic bottle that has two suction cups on it and a gasket that holds it flush to the stern when filling the tanks. As soon as I see a dribble going in the bottle I know I am "full".((You can't see the gasket in the photo...it is on the back side of the bottle))



no spill.jpgThe alternative is the "whistle". I don't have that gizmo but apparently it is an inline whistle, (inserted close to the tank in the air vent line), that puts out a "whistling" noise as the air is expelled from the tank as one fills and when the whistle stops....the tank is full as the whistle would have a bit of gas in it. As the gas is used the fuel drains back from the whistle into the tank...until next fill.

Unfortunately I can not use a "dip-stick" to check fuel levels as I have the anti-siphon tubes from the deck to the tank.

Just a note here about water getting in through the gas cap....(flush mount on a flat deck). I change the gasket every spring, (@1.65each) and when I winterize I run a thick bead of stop-draft, (looks like crystal clear silicon but does not stick like silicon), around each cap seal and in the Spring it just pulls off...no mess and guaranteed no water in the tank.
 
As soon as I see a dribble going in the bottle I know I am "full"
these things should never have been designed to allow that to happen.
It can become quite an expensive trip to the fuel dock if your caught accidentally dumping fuel in the water.
And what ever system the EPA finally allows for use should be made as idiot proof as possible.
I think putting the vent loop up high into an interior bottle has some merit. And truthfully, filling up is somewhat stressful to me as I am always wondering if fuel is about to pour out the vent.
I have also wondered about sending the exterior vent back to the fuel fill as it is done on cars and somehow retrofitting a charcoal cannister. I think the cannister might need to be larger? considering the fuel tanks size on boats compared to cars.

Does anyone have a link to info on a boat evaporative and diurnal fuel emission system control?

I have a fairly large long interior space directly above my twin saddle 150 gallon monel tanks made by SeaFair.
I could design a bottle with a 5/8 inch inlet on the bottom and a 5/8 outlet on the top which runs to the exterior vent. The bottle could be as tall and wide as 1 foot and I think would assure no fuel ever spilled out the vent. On fueling, as the tank approached full, that exit level in the added on bottle would be about 16 inch above the tank vent outlet and I think any overflowing fuel would be seen at the fill spout only.
I also wonder if in long ago days, people used to know their tank was full when fuel poured out the exterior vent.
 
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Yes, year ago no one really cared about a squirt of gas out the vent....could make it "disappear" with a squirt of dishwashing soap on the floating gas.....(really didn't disappear..just wasn't so obvious). We, as boaters, well most of us, became very concerned about pollution as time passed and now a squirt of gas on the water is not only frowned upon by the 'authorities' but also by fellow boaters. Any kind of pollution in the 1000 Islands is frowned upon and many of us have been known to jump all over a guy/gal who disposes of their cigarette in the water .....

As well, boats are forbidden to take on gas in our marina, (again 1000 Islands), because of not only the concern for a fire but also on the off chance of a spill. Caught fueling, no matter how big/small the boat is, will cost one $25,000.00.

I think the " no spill" bottle is a great idea. I carry a few Jerry Cans on board and any gas that 'squirts' into the bottle goes in the can and I use the collected gas for my Honda 2000 when running the generator on shore.
 
Imagine your boat fuel tank develops a leak.
The leak is fairly big
The bilge pump activates and pumps out the fuel into the water.
Boater has to declare bankruptcy since he cant pay the fines and or the lawyer and I think the law says he can be jailed.
 
Where do they fill up then?
Are you saying in the marina adding fuel from a can to your tank is a $25000 fine?
You must be talking about a fuel spill.

Yes, that is exactly what I am saying. This law came into effect just over three years ago when a boater was transferring fuel from a "can'" to his boat and there was an explosion and fire. He suffered 30% body covered with 3rd degree burns and this happened about 1/2 mile from the marina. There is NO FUELING of any kind in the marina.

About two years ago we had a sailboat that was leaking a very little bit of fuel into the water in the marina. He was towed out of the marina and could not return until the vessel was fixed.

Our marina does not sell gas. Gas must be purchased at a "gas dock" owned and operated by a private individual and is located about a mile east of the marina.

In my case I have about 6 twenty gallon Jerry cans onboard. I go down town and buy the fuel, (close to a dollar less a gallon than the fuel dock), transport it to my boat and then when I leave the marina I fill my boat out at one of the islands. I have not bought gas "on the water" for over three years now.
 
Applying a vacuum to a marine fuel tank is a very bad idea and can cause grave damage to both you and your boat.
for example:
One inch of hg vacuum equals .491 PSI, that would be exerted on every sq" of tank surface.
applying a 2" hg vacuum to a typical 48" x 24" x 12" tank exerts a force of over 1000
pounds on just the top surface of the tank. if you have a very large tank, it would not be structurally capable of withstanding the pressure.
48 x 24 = 1152 sq". (.491 x2) =1131.26

Secondly, the fuel pump would have to overcome this vacuum and may not be able to supply sufficient fuel at high RPM
Most auto evap systems have vacuum limits of .5 in hg and safety valves to prevent tank collapse.

Joe
 
I recall all cars tank caps have a pressure and a vacuum relief built in.
Neat idea. If pressure rises too high it vents, if pressure drops too low it lets air in.
when not needed to vent it is a closed system and most likely the seal is on for much of the day and the cap only has too open on extreme temp changes.
This would be a naturally easy retrofit on a tank vent line on a boat.

Mostly I have seen when opening my car gas tank a neutral pressure. BUT, sometimes If i open it real fast I get a tiny pressure poof off it.

On my boat vent line clamshell on the hull, I tend to stuff a paper towel wad into it to help keep the air exchange down. If refueling or running I need to remember to remove it.
 
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