Venting a Charcoal Carbon Vapor Canister...

[jim3326]

(If I could only figure out how to attach photos...)

Become a contributor.

 

[DaveyGeez]

I've managed to add a couple photos to My Gallery, but haven't figured how to get them posted in this thread.

 

[gr8scott]

Here you go Davey.

 

[McLeod]

I'm carburated, so i don't know, but I would think having the fuel return line and the vapor line attached next to each other like that would be a problem.

The top of the tank will almost always have an air pocket.

 

[DaveyGeez]

"The top of the tank will almost always have an air pocket"
Sorry, I don't understand.
There's always air on top, unless the gas has been topped off into the fill pipe. It's possible that happened and filled my vapor line, but I checked the cap pressure a few times and never found a build up. So I can assume the vapor was flowing to the canister, until of course, fuel filled the line. I'm still blaming it on the steep, greater than 16% downhill grade.

Getting back to your statement, are you saying the return fuel is blocking vapors from flowing out? If that's happening at the vent tube wouldn't the vapors escape up the fill pipe then down to the vent tee?

Still looking for a float style check valve...unless that Coyote will work in this case.

 

[DaveyGeez]

Okay Maui, how did you do that?
I looked all over for the "BB code".

 

[DirtDonk]

URL? Really? I can't drag/drop from my files?
Guess I need help with that too

As you found, you need to either use your Gallery, or Garage features, or pay 12 bucks a year to become a contributor to post directly to a discussion from your device.
The URL it was asking for is when you use an online image hosting site elsewhere (such as SuperMotors and the like (but not that other one!)) and post up there, linking it to your discussion. Works for lots of members, but I prefer the direct route myself.

Paul

 

[DaveyGeez]

Ah-ha! Thanks Paul.

 

[DirtDonk]

Is there any way to create a "Y" fitting rather than the "T" fitting for the return line Davey?
Aim the one leg towards the tank rather than straight into the hose, getting more of the liquid back into the tank quickly.

And that's quite the tank. Looks very nicely made.
While it's out, can you check the filler neck as it enters the body of the tank to see if it's flush with the tank wall/top surface, or if it extends into the tank at all?
The extension (if present) acts to retain an air pocket at the top most level of the tank. Judging by the angle, it's possible that it still creates a slight pocket, but if it extends into the tank a little more, that leaves a larger air pocket for expansion.

Where the vent is now, it would seem that when the engine is not running there is no problem even on a large incline. But with all that fuel from the return splashing right into the vicinity of the EVAP pickup, it might just be picking up more liquid on that same incline.

Is the hole at the top of the tank for the sending unit? Any chance you could put a fitting on that part instead?
That might do the trick.

Good luck.

Paul

 

[DaveyGeez]

It might be easier for me to raise the vapor line further up from the fuel return tee.
Funny you should mention the fill pipe extending into the tank to create an expansion area. this was brought to my attention a couple years ago, and modified, but it didn't make sense then nor now. How can an air pocket be created when there's a vent tube right next door?

As for the craftsmanship, thank you, but I wish there were baffles inside. 30 gal. is a lot to be sloshing around, not helping the situation.

The tank was re-installed when I added a new sending unit and the vapor line. In any case there is no room at the top of the tank as it presses against the floor pan where the spare tire sits. The talented fabricator fulfilled my request for the biggest tank that will fit.

 

[DaveyGeez]

I sent a query to Coyote regarding their rollover valve.
It uses a steel ball and will only stop fuel flow with a rollover. Won't do anything until that ball settles into place via gravity.

 

[DirtDonk]

How can an air pocket be created when there's a vent tube right next door?

This is why it's illegal to "top off" your tanks. At least in some states.
Because the evap vent lines are never going to be large enough to allow the tank to fill the void before the fill-vent back feeds and shuts off the pump. Which is what allows the large air space up top to remain air.
Since there is no inward pressure once the pump is shut off, the air space remains and gives the fumes the chance to exit through the venting system.
But if you literally top off the tank, then the air space can be forced above it's normal capacity. The air flowing out the vent is very minimal, but the much larger filler neck vent will let the liquid displace the air.

Pre-evap vehicles still had the air space, but you could literally fill the tank right up to the gas cap without harming the system if you kept topping it off. Because there was no venting system to mess up.
The good news is that you got extra gas for your trouble, but the bad news is that if you parked it right away without driving it enough to lower the level, the next time you came out to your parked car you might have a big flowing mess of gas spilling out the filler neck.
It's actually one of the design reasons, other than pure aesthetics that even back in the fifties and sixties, and maybe before that, you had a lot of cars with recessed gas caps behind doors, license plates, tail lights and other places along with drain holes that directed spilled gas out and down to the pavement. Great for paint, but not so good for a hot stinky garage!
Trucks were usually not so lucky. They got relegated to "who would care about the paint" crowd, to the "truck owners know not to over-fill anyway" crowd, and the "why should be care about the end-user as long as it costs less" crowd, during the design process.
Look at any old car or truck with a visible gas cap out the side of the body and if the owner was a topper-offer type, you likely saw the paint damage from the filler cap to the ground. We don't see that as much anymore, but still some old cars are running around like that. My own '68 is having that problem and I'm not a topper-offer (any more that is;D)!

So any time you see someone, or you are that someone, that is clicking the pump trigger and re-clicking and re-clicking to get that last little bit of gas in the tank, what is going on is the air space is slowly being replaced by liquid.
Alternately, stopping your fill process when the gas pump shuts off the first time (when it's working properly at least) maintains the required air space.

Every vehicle, even brand new ones, can sometimes shut the pump off falsely early depending on the pump nozzle being used. Once you know your individual vehicle and it's pumping characteristics though, you can determine whether it's actually full, or needs another bit of pumping.
In the old days we were expected to just know how to top-off correctly for circumstances, or suffer the consequences. Now it's a legal thing because it's more about keeping the air clean on the one hand, and not damaging the (VERY EXPENSIVE!) EVAP system on the other.

Paul

 

[DaveyGeez]

Thinking out loud:

I've ruined a charcoal canister and separating liquid fuel from vapors in the vent line is a challenge without a separate expansion tank. Drilling a hole in the gas cap would be simple, but not ethical. Since fuel vapors are heavier than air, why not forego the canister and run the vent line directly to the air cleaner? While the car is running the vapors will be burned. While it's parked the vapors should settle back into the tank or condense in the line, ready for burning next time it's running.

I'll move the vent tee up from the return fuel line and add a high loop to the line to minimize direct fuel flow into the vent line. Condensation will have to evaporate or get blown into the carb with tank pressure buildup.

I tend to overthink, missing the simple solution and this may be one of those cases.
Thanks for working through the process with me.
Davey

 

[DirtDonk]

I've ruined a charcoal canister and separating liquid fuel from vapors in the vent line is a challenge without a separate expansion tank.

There have always been two schools of thought regarding charcoal canisters.
One is that they are dead as soon as liquid gets into the media. The second is that they are "re-chargeable" with heat.
The writeups back in the day used to involve using an oven, but seems to me the last thing you'd want in your own kitchen oven is something evaporation gasoline fumes! However there may be something to that after all.

Setting it upside down to drain out first, then setting it out upright in the sun on a hot day might be enough to do it. Or even on multiple days. Especially handy if you live in a hot climate.
After all, the top ports are all vents, right? So theoretically there is enough evaporative capacity to eliminate the liquid relatively quickly I would think.

The only question then, is does the liquid in the tank actually effect the charcoal in such a way as to render it useless even after it's dry.
I smell a YouTube search coming on...

Drilling a hole in the gas cap would be simple, but not ethical.

Good on you for thinking along those lines. I feel the same way.

Since fuel vapors are heavier than air, why not forego the canister and run the vent line directly to the air cleaner?

It sounds reasonable that the vapors are heavier than air (I think I've heard that too) but is that always true? Or is there a temperature aspect to that equation? Something else at work?
If it was always heavier than air it would not flow so easily out the top vents except during expansion. And I think it would not be so easy to smell evaporating gas from a spill nearby, or an open gas container.
Then again, perhaps in that spill/container scenario we're just dealing with the vapor being carried on the breeze.
Interesting to think about just what is going on.

While the car is running the vapors will be burned. While it's parked the vapors should settle back into the tank or condense in the line, ready for burning next time it's running.

It sounds reasonable on the surface, but something seems to be off. Maybe it would work just fine, but is simply less efficient at it than a canister? Or maybe there are too many conditions where the fumes would continue up the line to the air cleaner even with the engine stopped. In those cases it would surely stink up the place around the engine compartment (think garage) as the vapors continue to filter up and out of the housing.
I'm not really sure though. And see nothing against giving it a try.
Especially with a loop or "P-trap" arrangement in the line.

I tend to overthink, missing the simple solution and this may be one of those cases.

Yeah, maybe. But isn't it fun going through all the thought processes while over-thinking stuff? I think it is!

Paul

 

[DaveyGeez]

Under the wagon again...familiar song?
I've been wondering all along why is there a stock vent tube parallel to the fill pipe? (Check the notated photo in my Gallery.) It connects to the fill pipe just below the cap and they both enter the gas tank at basically the same place. Maybe the stock tank in a stock '56 wagon there was a good reason, but I can't reason it now.
So...I'm thinking...again, why not run the return fuel line directly into the tank vent (not a tee) and run the vapor vent line into the top of the fill pipe separating the two entirely. Is there some reason you can think of for the current parallel configuration?

(I added a notated photo of the vent/filler pipe to my Gallery showing my proposed routing.)

 

[DirtDonk]

I've been wondering all along why is there a stock vent tube parallel to the fill pipe?
It connects to the fill pipe just below the cap and they both enter the gas tank at basically the same place.
Maybe the stock tank in a stock '56 wagon there was a good reason, but I can't reason it now.
Is there some reason you can think of for the current parallel configuration?

Every tank on every vehicle I've ever seen from '64 models to 2004 (haven't looked at a 2019 with cap-less filler neck yet) has the tube we commonly call a "fill vent" and it's always been for the same thing that I know of.
I've never questioned or second guessed it to this point, so shame on me for not looking into it more, but I was always told it's what helped to smooth out the filling process, but more importantly to shut off the automatic filler nozzles at the gas station.
Never occurred to me to question the nozzle shut-off part of that equation, but then I've never had a hankerin' to modify one either.

Time for me to do some more research then I guess. But until I hear differently, I would not eliminate that tube and repurpose it as one half a return line.
A smooth and effective return line exiting directly adjacent to the fuel pump pickup is always what I was taught was the best. Not just throwing the returning fuel into the top of the tank. I don't imagine that air bubbles remain in suspension long enough to get sucked up into the fuel pickup and cause pumping trouble, nor do I imagine that it's a bad thing when the tank is almost empty either, since at that point it's not picking up fuel as efficiently anyway.
Although that's what the design of the sock filter does in fact. Any fuel that touches it gets absorbed into the material to be sucked into the pump.
But if you look at any modern return system the return fuel is in fact returned to the tank right at the pump pickup. Not some random spot near the top of the tank wherever the filler neck happens to be.

So no, until someone clarifies the function of the fill-vent I can't say it would be bad. But no, I don't think it sounds like a good idea either at this point.

But heck, Bronco tanks are such notoriously poor fillers, it would be very interesting to experiment with eliminating the normal fill vent to see if it helps!

Paul

 

[DaveyGeez]

Thanks for your thoughts Paul. You bring up a possible problem with my custom tank. In addition to not having any baffles, the fuel pickup has no sock filter. It's simply a stainless tube entering on the front side of the tank through a welded fitting, turning down and welded about 1/4" off the bottom. There's an inline filter (100 micron I think) before the inline fuel pump and another (10 micron) after the pump near the EFI. The return fuel enters no where near it.

Judging from filling a JerryCan I don't think the fuel flows from the gas station nozzle fast enough to block air/vapor flow out of the same 2" diameter fill pipe. There's never been a problem filling the tank nor has there been an obvious combustion problem resulting from bubbles in the fuel.

I might as well break another customary design rule and see what happens. Probably easier than trying to research the situation.

DaveyG

 

[jim3326]

The fill vent is meant to prevent the fuel from getting pushed back up the filler neck because of the air being displaced by the fuel being pumped in. Now there is no reason I can think of that you couldn't tee into it for the canister.

 

[DaveyGeez]

Jim, my problem was fuel running up the vent line to the canister. Guessing it was caused by the fuel return line also teed into that fill vent I've separated them by breaking the fill vent between the two. Your explanation for the function of the fill vent sounds logical. My next gas station fill-up will test it. I'm hoping the 2" fill pipe has enough room for fuel to enter and displacement air to come out without triggering the shut-off. I'll let you know.

 

[DaveyGeez]

It worked!
The stock filler pipe vent tube has been repurposed. It is no longer continuous. My EFI fuel return line uses the bottom portion to direct fuel back into the tank. The remaining upper portion, where it tees into the filler pipe just below the filler cap, vents tank vapors directly to the charcoal canister ( I don't think the charcoal is useful since it was flooded with fuel), then to the carb air cleaner. As I guessed, the 2" filler pipe is large enough to allow fuel in and air out at the same time.

Note: According to my sources, activated charcoal that has been contaminated with gasoline requires temperatures of 350° to reactivate.