Tank vents and rollover valves

I would like to open a discussion on these very topics. I became interested in them as I began setting up my tanks. I am trying to setup a system of linking the tanks and using only one set of pumps. My first problem arose when I had the system that I thought would work, to find that fuel being pumped into my reserve tank(the one without the pumps), was filling faster than it was being shunted back to the primary tank, and fuel began shooting out of the vents on the front of the tank.
Well I think I have solved the problem, but it got me to thinking that I needed a system that would protect me and all the owners of GT-40s from the buildup of pressure in the tanks. Scenarios range from parking on hills to rapid deceleration, rapid acceleration, and heavy cornering. For those of you with the selector valves, how about one of them getting stuck or gumed up causing the fuel to go where you don't want it, say,, all to just one tank!!
The easy answer to this is vents in the front and rear of the tanks. The part it doesn't answer is the safety of using them and what type. One answer is to install a rollover valve which allows you to keep from spilling gas in the event of a rollover, and it allows for the free flow of air into and out of the tank. The problems with this is it allows the free flow of gas vapors out of these lines as the gas is heated(sitting in the sun) or gas is sloshed around in the tank under the scenarios outlined above, as well as when you fill the tank at your neighborhood gas station, or the stuck valve scenario. Some of the rollover valves are large and won't stop the flow of gas up the line and into the front or rear clip area in an upright car.
It was mentioned on another thread that the individual posting didn't like fuel near electrical devices or electricity. Lets look at the various vents in these cars. The front vents are usually mounted near the fuel filler caps. Well if you mount your battery in the front as mine is, the vapors will sink down into the front clip area as well as out the sides, and near the fresh air intakes on some of our cars, which leads to gas vapors entering the cabin. Not good. Vapors around the battery and other electrical appliances could lead to bad experiences.
In the rear the same thing happens except it is behind you and probably few if any vapors get into the cabin, but all do go into the rear clip area. What do we have there, but hot exhaust and electrical appliances again.
Most modern cars have rollover valves built into them now. The outflow of these lines usually goes to a Charcoal canister to absorb the fuel vapors. On most of these fuel tanks, there are one or two, fuel vapor valves as well as a vent line up the fuel filler line to help prevent air pockets from forming and not filling the tank. These valves are small valves that will stop the sloshing of the fuel up into these vent lines that lead to the antirollover valve, which leads to the charcoal cannister. Some are built together as one piece.
I don't think I have seen one GT-40 that utilizes a fuel vapor valve that prevents the sloshing up into the vent lines or a charcoal canister(could be wrong on this one). Just the rollover valves. Most of the space frame cars and probably some of the monocoques have the room for the canisters in the front besides the filler tubes where they wouldn't be seen, so that doesn't seem to be an issue except there would be little hoses running all around the car, or lots of little canisters stashed all about the car.
So other than from an environmental issue of fuel vapors to the atmosphere, why don't we use the vapor valves and the carbon canisters? Just because our cars may be exempt from emissions doesn't mean we shouldn't think about it.
I for one plan to use the vapor valves if nothing else than to keep the fuel from sloshing up into the vent lines(as they have once). I will also use the rollover valves. I am undecided about the canisters since mine is not on the road yet.
What are your thoughts on this topic(s). Am I just blowing hot air up your skirts over nothing or is it a concern that we should address in our builds?? Are the vapors so small they aren't a concern??What do you think??

Bill
 
Bill, I take fuel vapors seriously. I have not heard of any GT40 or similar fires or incidents due to fuel vapors (doesn't mean there weren't any). I plan on a separate
vent line and hose to a location very high and outside of the bodywork. I'll use a marine fuel tank vent fitting, (or a roll over valve) and Aeroquip push lock fitting at the tank. The vent will protrude above the bodywork slightly and will be covered by a homemade clamshell, something like a blister but opened on one end. No vapors entering the engine space while running or refueling. I could run the vent line next to the fuel fill as an alternative on the SL-C. Probably overkill, but that's what I'm doing.

For the GT40 think about how you could vent next to the fill caps and affix some kind of neoprene pad around the fill & vent to close-up the bodywork preventing decending vapors from entering the front clip. Something to think about...
 

Trevor Booth

Lifetime Supporter
Supporter
The probability of fuel vapours collecting in the front and rear areas to be an explosive mixture is virtually nil. The mixture would be too weak.

I ran vent line in steel tube from rear of tank to filler, see attached photo.

A sealed screw in cap fits into the ULP restrictor and prevents fuel sloshing up the filler neck in case of a frontal impact, the cast aluminium cap is just for effect and is not sealed when closed and latched. And it works as I tried it out !!

You could run the vent line to a carbon cannister (activated charcoal) which is then in turn connected to the inlet manifold so collecting fuel vapours.
 

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Trevor,
I notice that you have a piece of weather seal on the leading edge of the sil in front of the filler cap. Does it run the full length of the sil? If so, that would serve two functions. One to keep water out of the front clip, and two to keep any fuel spill or heavy vapors that might collect there and force them to the side and away from the clip. that is something that I am considering also.
What was the speed at the time of impact on the front clip? Do you think that was enough for the fuel to slosh up the filler tube? The reason I ask is some of the tanks are built with plates internally that form a vertical slit that slows down the movement of the gas and would absorb a lot of the force of the gas moving under impact. Instead of having 10 or so gallons moving at one time to the front, you would have a few hundred cc moving to the next chamber and so on to the next chamber leaving a gallon or two to exert pressure on the filler neck.
I have a tight seal screw on filler cap under the LeMans flip up unit. So no slosh would go up the tube. Air pressure would prevent it. If I put a fuel vapor valve in the vent line, it should stop any slosh. The rollover valve in my front vent line would close under the force of the rapidly moving gas if the vapor valve failed. At least I think it would as I plan to use a small 3/16 size unit rather than an 8 AN that I have seen for sale. The weight of the ball in the valve would be a lot less.
Does the vent from the back of your tank, that goes to the filler have any sort of devise that would prohibit flow of gas up from the rear of the tank if you were parked facing up the hill? Do you have a vent from the front of the tank to relieve any pressure that would build up under this scenario?
I am just trying to see if all the bases are covered.

Bill
 
Bill, Complex subject ! As far as positioning the main tank vents, take a glass fish tank ( bear with me on this one ) half fill it with water, then move it longitudinally in both directions and watch the results. Considering that you always want the main vent in air rather than liquid, and that the liquid will move either forward or backwards ( braking/acceleration ) the the obvious place is as high as possible in the centre of the tank, which will always be in air. A secondary vent in the filler neck to prevent blow back when filling should only be open to atmosphere when the tank is being filled i.e. the opening to the vent should be below the sealed filler cap. Care must be taken in the overall fuel deivery system, and particularly in relation to the control of fuel in the tanks. Whether you decide on a completly atmospheric pressure in the tanks, or a negative or a positive pressure, is down to the individual design, but considering that fuel is potentially the most dangerous thing in the car ( after the driver of course ) it must be treated with respect. If you are useing a dead head system negative pressure can be induced into the tanks, if you decide on a full by pass system, recommended for any car exceeding 400hp ) the positive pressures can build. These tank pressures will have a real affect on the fuel delivery to the engine and the settings of the pressure regulator, so think it through carefully and test everything as you go. For safety and mechanical isolation, I use electrical solenoid valves on both the tank vents and the fuel return lines, switched from the feed to the individual pump being used, this means that if the right hand tank is in use, the left hand tank is completely sealed and isolated, and also that in the event of any emergency the electrical kill switch will automatically seal the fuel sytem to the whole car. Ask if you need further info. Frank
 

Jim Rosenthal

Supporter
Tanks should be internally baffled to prevent sloshing (AKA "free surface effect"); I've been wondering about the venting question as well. I don't think it's a trivial one either; where would I get charcoal canisters to absorb the fumes of gasoline from the overflow vents?

In principle, the idea of venting the tanks to a point highest on the car is sound, I think. Also venting them outside the car. I wonder what was done in the era before fume capture and recirculation systems as cars have now? The gasoline equivalent of the road draft tube?
 

Trevor Booth

Lifetime Supporter
Supporter
Bill,
yes there is a weather strip mainly to stop water spray.

Hit a tree after breaking right rear lower wishbone, was doing about 90MPH when it let go so probably down to 50 at impact.

The tanks are foam filled with 10% in rear half and 15% in front half.

If you are parked up hill or down hill the pressure in the tank is vented by the vent tube in any event. The vent line exits a 50mm dia x 50mm high upstand at the rear of the tank. (This is screwed down to the tank as you cant get tank in ) The line (5/16 steel bundy tube) then runs on the outside of the side sponson (under the FRP skirt) and up to the filler.

The fill tube below the screw in cap is 65mm Dia and a 20 litre fuel churn can be upended to dump the fuel in-- no splash back occurs. You may need a secondary filling vent if your fill line is small diameter. at a guess anything below 40mm

A breather in the centre of the tank wont work unless you fill the car with it dead level, if the car has a nose down rake , which it should have, you will trap air in the rear half of the tank and it will not be completely full.

Each tank has a gated surge tank about 150mm long built into the tank at the rear end and the vent line is in top of the surge tank volume.

This car has done two Targa Tasmania , a very tough tarmac rally with many sharp bends , uphills down hills. It has done lots of race meetings since. It cranks out 470 FWHP and I have seen 145 MPH with a gear to go. Never a fuel problem at any stage.
The car was built for competition not road use.

I am not a fan of fancy external surge tanks and lift pumps and all the associated joints and leak potential.

You could run the vent line from the tank up the B pillar and back down to an ACC ( one for each tank) via vapour valves if you think you need them. You could place a ball type rollover valve in the vent line at the tank or you could put it on the down side where vent line runs back down the B pillar. Have a look at Highway Trucks (Tractors) side mounted tanks and you will see them.

If you are running EFI you could run the return lines to the front of the tanks to return the hot fuel then run a balance line between both tanks and draw off both tanks all the time.


You could put solenoid operated shut off valves, as Frank Suggested, connected to an inertia switch (common in a lot of US cars) and or the battery kill switch or in the pump supply circuit or even by an oil pressure switch.

The main thing is to keep it simple, a minimum amount of joints and make sure you dont get pos or neg pressure in the tanks as Frank pointed out pressure + or - can cause big problems.
 
where would I get charcoal canisters to absorb the fumes of gasoline from the overflow vents?

I'm also curious where one could get a charcoal can that they could install inline in the vent line in order to absorb any fumes.
 

Randy V

Moderator-Admin
Staff member
Admin
Lifetime Supporter
I'm also curious where one could get a charcoal can that they could install inline in the vent line in order to absorb any fumes.

Any auto wrecking yard should be able to help you out...
 
Any auto wrecking yard should be able to help you out...

I was reading more about charcoal cans, and everything i read says something like the can absorbs and then re-circulates/releases the fumes to the intake?

If I don't care about about recirculation and I plan to just vent the other side to the ground (so it goes tank -> can -> ground) am I wasting my time with a charcoal filter, or will it still dissipitate fumes that come through the vent line?
 

Chris Duncan

Supporter
This topic is interesting to me because I'm still trying to figure out how to vent my tanks.

First I tried a one way valve. That didn't work because while it allowed air in as the fuel was used it didn't relieve pressure buildup, like on a hot day.

Also tried just running small hose from the top of the tanks to the top of the engine compartment. This is no good because when the tanks are full and the car is on a slope fuel gets into the vent lines, then a little pressure pushes it up and out.

Thinking my main problem is I have no risers in the system, IOW the gas caps are right on the tops of the tanks. So there's no where to put the vent lines other than right on top of the tank.

Most of the rollover valves I've seen are steel balls operated by gravity. This doesn't work for liquid fuel that's pushed up the line by tank pressure. What I think I'm looking for is a float type check valve that closes with liquid (fuel) but allows vapor to pass both ways? Anyone know a source?

Gave a thought to carbon canisters, but they would still have to have some kind of check valve system to keep them from getting inundated with liquid fuel. Another problem with canisters is you need an airbox to distribute the canister vent, which is problematic with the typical 8 stack induction. It probably would affect cylinder balance if you had the canister vented to only one stack.
 
I was reading more about charcoal cans, and everything i read says something like the can absorbs and then re-circulates/releases the fumes to the intake?

If I don't care about about recirculation and I plan to just vent the other side to the ground (so it goes tank -> can -> ground) am I wasting my time with a charcoal filter, or will it still dissipitate fumes that come through the vent line?

The charcoal canister is an emmissions-only thing (and one of the earliest) with no performance-related benefit or detriment. It is pretty simple; the charcoal holds the fuel vapor until the engine develops vacuum to pull the vapor into the intake manifold. That's it. That's all the charcoal canister does.

If you plan on running the downstream side of the canister to atmosphere, don't bother with it. If you run the downstream side to the engine, tap into the intake manifold. Cylinder balance probably won't be an issue because the vapor is cleared rather quickly from the charcoal (unless you have other issues leading to excess vapor or even liquid entering the canister).

To address an earlier question about what was done pre-emmissions...nothing. Tanks were not sealed (or pressurized) and vapor would just come out of the filler neck. Ever see a filler cap from a muscle car or anything pre-emmissions? Just metal; no seal. And, yes, if you filled the tank too full (as in up the neck) you could drop the hammer and end up with fuel running out the back of the car (remember, the filler tubes were down behind the license plates).

Would I use a charcoal canister? No reason not to, but I would tap into the manifold instead of letting the stored vapor be released to the atmosphere.

Eric
 

Chris Duncan

Supporter
If you run the downstream side to the engine, tap into the intake manifold. Cylinder balance probably won't be an issue because the vapor is cleared rather quickly from the charcoal (unless you have other issues leading to excess vapor or even liquid entering the canister).
Eric

Agree carbon canister doesn't affect performance. But tapping into the intake is problematic with individual/separate intake runners. If you come in below the throttle plate it's going to affect the mixture on that one cylinder because it's bypass air. Not just the fact it contains fuel vapor but because it's un-metered air on just one cylinder.

thinking you could just dump into the top of one of the air horns. You're probably right that it's not that much vapor to have any prolonged affect on runability

my setup does have a small vacuum junction block fed by 3/16 lines from each T-body below the throttle plates. However this is what feeds the vac signal for the MAP sensor so guessing a (sometimes) open line connected here would throw that off.

this still doesn't address the need for a check valve. All the early canister setups didn't have one(?). The later ones may but they involve electronic control. When my tanks are full and the car is stopped on a hill (Seattle is all hills) there's fuel running up the vent lines. A canister is going to be overloaded.
 
This topic is interesting to me because I'm still trying to figure out how to vent my tanks.

First I tried a one way valve. That didn't work because while it allowed air in as the fuel was used it didn't relieve pressure buildup, like on a hot day.

Also tried just running small hose from the top of the tanks to the top of the engine compartment. This is no good because when the tanks are full and the car is on a slope fuel gets into the vent lines, then a little pressure pushes it up and out.

Thinking my main problem is I have no risers in the system, IOW the gas caps are right on the tops of the tanks. So there's no where to put the vent lines other than right on top of the tank.

Most of the rollover valves I've seen are steel balls operated by gravity. This doesn't work for liquid fuel that's pushed up the line by tank pressure. What I think I'm looking for is a float type check valve that closes with liquid (fuel) but allows vapor to pass both ways? Anyone know a source?

Gave a thought to carbon canisters, but they would still have to have some kind of check valve system to keep them from getting inundated with liquid fuel. Another problem with canisters is you need an airbox to distribute the canister vent, which is problematic with the typical 8 stack induction. It probably would affect cylinder balance if you had the canister vented to only one stack.


Hi Kalun

ever checked on the 90´s DUCATIS . They have a nice alu vent valve with a spring loaded plastic ball. So it is always closed and keeps the pressure in the tank ( motorcycle with full tank in bright sunlight), but the spring is weak enough to open as soon as you have vacuum created by your fuel pum. On my gravity feeded motorcycle i replaced this spring with a weaker one out of a ball pen. Don´t know if they would flow enough air, but the princip is great. my you can modify a stock steel ball one with a spring and or a plastic ball. There are also good ones already incoorporated in fuel hoses from the MX aftermarket supply ( if they hold fuel after a jump they will hold anything).

Acerbis_tankentlueftung-alu.jpg


TOM
 
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Chris Duncan

Supporter
So it is always closed and keeps the pressure in the tank ( motorcycle with full tank in bright sunlight),
TOM


Yes Tom, I tried a one way valve, it vents fine but it builds too much pressure. These tanks/fuel system really aren't designed to be pressurized. They are larger and more complex than a bike.

When I built them I tested at about 10 psi and the sides were already bulging because they are flat and long. Can't imagine what pressure is building on a hot day but it's got to be more than 10 psi and that's not good.
 

Chris Duncan

Supporter
What I was imagining actually exists, imagine that. It's called a discriminator valve.

Pegasus - Aluminum Discriminator Valve, 12AN Male Fittings

Poly Performance JEEP/TRUCK & BUGGY*::*Fuel Cells & Tanks*::*Fuel Safe*::*Fuel Cell Accessories*::*Discriminator Valves - JK Synergy Suspension Systems, Fox Racing Shox, Beard, CTM, Johnny Joints®, Currie Enterprises, Edelbrock, Pit Bull Tires, Ramse

It's a float type valve that vents vapor but closes with liquid fuel. This version also has a gravity rollover valve in addition to the float. A little on the expensive side but you could run just one with a T going to both tanks.

Need to find just a float valve and add one of the less expensive rollover valves.
 
Agree carbon canister doesn't affect performance. But tapping into the intake is problematic with individual/separate intake runners. If you come in below the throttle plate it's going to affect the mixture on that one cylinder because it's bypass air. Not just the fact it contains fuel vapor but because it's un-metered air on just one cylinder.

Kalun

Where does your PCV valve feed? Into the intake manifold? If this is not a central location (feeding all runners), then you'd have the same balance issue you are concerned with in feeding to one runner. If you think about it, in many production vehicles neither the PCV nor the EVAP canister (charcoal canister) feed all runners, often just one bank or the other (in a V-type engine).

Just my learned opinion, but I don't think you are going to have an issue feeding one runner. You will likely need to adjust that one carb richer than the others, but the airflow should be consitent through the canister.

For what it's worth...

Eric
 
"If you think about it, in many production vehicles neither the PCV nor the EVAP canister (charcoal canister) feed all runners, often just one bank or the other (in a V-type engine)."

Eric,
Modern FI systems have one large throttle body that feeds all the cylinders, so venting to the manifold will get the extra air/vapors to all cylinders. Kalun is right in that if you have a central vacum source for the 8 port FI it will alter the ECU settings, and I would bet that if you vented to one port and put an O2 sensor on that exhaust port it would read different from the others. Either that or the ECU would be working overtime to try and get the setting on that one port to optimum.


"A little on the expensive side but you could run just one with a T going to both tanks."

Kalun,
You couldn't do that because the valve is vented on the sides allowing air to escape around the ball. If you did this arrangement, you would have to have a small can(slightly larger than the discriminator valve) that both tanks were connected to and the discriminator valve was at the top of that can. WOW, it just hit me, if you did it that way, you could connect all 4 corners of the tanks to the can. The can would have to be mounted a bit higher than the tanks and then vented. Anyone see a problem with this??
I am wondering, if you had one valve at the rear or center, would it close if pressure were to build up in the tank forcing fuel up the line(Front vent not operative or center vent only vent line)?

Bill
 

Chris Duncan

Supporter
Eric, TWM induction runners totally separate except for small plenum to feed MAP. No PCV. Some people have built a large plenum under the manifold valley, you have to if you want to run IAC.

Bill, my understanding of the discriminator valve, it shuts off with liquid fuel coming up but allows vapors to pass both directions.

the ones you are looking at with holes on the sides are made to be mounted directly on the tank, the holes will be inside the tank. The one I was thinking of has fittings on both ends.

Poly Performance - Detail Image Viewer

here's the manufacture's site, a little less expensive, and the in-tank one could be mounted on a small catch can, so $88 and build a small catch can.

http://www.fuelsafe.com/store/parts-accessories/discriminator-valves.html

I too was thinking about a can because of this thread, just like a pint or so, it's not that much fuel that gets out and it's not for that long of a time, if it was just contained it would drain back. It's only while the tanks are full or near full, and they get drained down pretty quick:laugh:.
 
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Julian

Lifetime Supporter
I have just come across and read through this thread and have a few comments;

1. Fuel tanks are not pressure vessels and should ideally be under no more than atmospheric pressure, why would anyone be considering anything that allows pressure to build up? 10 psi in a fuel tank is a lot of pressure. If your tank has no vent to atmosphere, fuel starvation will umtimately occur or the tank will collapse. Also consider what is going to happen when you go up or down in elevation, the tank has to be able to compensate for pressure changes.
2. Vent lines, whether through a canister or not should not be connected to manifold vacuum. The vacuum from manifold combinhed with fuel usage will collapse the average tank, plus one backfire and the flame front is potentially heading back to your fuel tank. The vent should be connected to the base of the air filter, ideally via a canister.
 
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