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Topic Review (Newest First)
08-14-2007 07:56 PM
charcoal canister

There seems to be disconnect how the evap system works and how you think it works. I have to agree with Streetrodderbn. All the vent hose on the tank does is allows the fumes from the gas tank to flow into the charcoal canister by themselves. The vacuum that purges the canister is prevented from reaching the gas tank by a check valve. The check valve is built into the charcoal canister. When the vacuum is applied to the old style canisters the fumes from the canister are sucked into the engine along with fresh air through a filter at the bottom of the canister. Look closely at your picture and you'll see what I'm talking about. Then again, maybe I just misunderstand what you're saying.
08-14-2007 02:18 PM
streetrodderbn just a question, if you allready have a "vent tube"exiting outside the car, and still have a gas smell eminating from the tank in the car, how would adding another vent (charcol filtered or not) solve the origional problem? NEVER PUT SUCTION OF ANY KIND pcv valve or other on a fuel tank vent!!!! You are asking for catastrophy!! I would concentrate on the cap on the tank,being the malfunction,or a pinhole in the tank top.(easy to check,just empty the tank of fuel,plug the feed line, and pressurise the return line with 5lbs of compressed air) I have used the exact tank in at least 10 applications for customers, and not had a gas smell in the car! these are even smaller cars without sealed bulkheads between the trunk area.
08-14-2007 10:32 AM
Charcoal Canister

That's about as simple as it gets and will work fine for your application. You might want to add a rollover valve so if your rod ends up on it's roof gas won't be pouring out. What is the system in the picture from?
08-14-2007 07:51 AM
bentwings I'm doing some research on the evaporative systems and found almost exactly as you described. I believe you are right. No need to make a complicated system. Even if I have to clean the canister occasionally. What are streetrods for but keep you busy. I'll use the extra AN-8 for a vent to incoming air I think rather than the cap. Possibly a power brake check valve.

Thanks for the years to look for, that will be a big help. I asked how much the canister was worth at the junk yard and he said $7 so it's done deal I think.

I was on the way to the junk yard yesterday to find one but I got interrupted by a dog that needed some pets. haha It's hard being newly retired and doing nothing but waste time on that dumb streetrod as my wife says. I told her the only time I wasted was the 2 hours I spent in bed...sleeping. haha
08-14-2007 06:24 AM
Charcoal Canister

If you can find a vacuum schematic of an '85 Chevy with a carburated 350 you can see how they connected the charcoal canister. The PCM doesn't control it. For your application you could probably forget about the TVS (thermal vacuum switch). The TVS doesn't allow the system to purge until the engine's warmed up.
08-14-2007 06:09 AM
bentwings I'm the manufacture of this tank and I don't smoke.

The outside fill pipe that will eventually be installed will have a fill pipe vent to aid filling but not vented to the atmosphere. Venting will be done through the vent fitting to a canister.
08-14-2007 01:26 AM
Originally Posted by bentwings

It's not the exhaust fumes. It's gas fumes from the fuel tank mounted in the trunk area. Even though the trunk area is sealed off, when filling the tank some fumes remain in the trunk. Eventually there will be an external filler. The trunk is well vented. There is an external vent ( outside of the trunk) on the tank too, but if the car just sits on a hot day the fumes will get into the car, this is what I'm really after.

The focus of the exercise is to vent the tank so fumes don't get into the car by the venting. There is an external vent but by capturing this I hope to clean up the car.
How does the manufacturer of the fuel cell suggest venting? There is usually a vent associated with the filler pipe.

You don't smoke do you?
08-13-2007 09:11 PM
bentwings I have an AN-8 male vent fitting and a screw on cap with no vent (Chassis shop 2"). Also I have a AN-8 male return that is capped.

here is the cad jpeg. It's about 16 gallons. 20 x 15 x 14.5. 14 ga 5052-0 aluminum.
08-13-2007 03:35 PM
Charcoal Canister

You're on the right track venting the vapors to a charcoal canister. Is there already some sort of a vent in the tank, or does the system you have now rely on a vented gas cap to relieve pressure in the tank?
08-13-2007 02:44 PM
bentwings Sorry for the confusion. It's not the exhaust fumes. It's gas fumes from the fuel tank mounted in the trunk area. Even though the trunk area is sealed off, when filling the tank some fumes remain in the trunk. Eventually there will be an external filler. The trunk is well vented. There is an external vent ( outside of the trunk) on the tank too, but if the car just sits on a hot day the fumes will get into the car, this is what I'm really after.

The exhaust is out the rear past the body lip and does not leak.

The focus of the exercise is to vent the tank so fumes don't get into the car by the venting. There is an external vent but by capturing this I hope to clean up the car.
08-13-2007 12:56 PM

I have been watching this thread for a few days and the confusion it is causing me makes me want to ask;

You have a fuel system that is running so rich that fumes are drawn into the passenger compartment? If so, an EVAP (or similiar) system is not going to help much. EVAP is designed to contain fuel vapors while the car is off and then burns the excess fumes while running.

Is the engine carbureted or injected? For a EVAP to work anywheres efficiently, you will need at the least closed air cleaner(s). EVAP also vents the fuel tank and carburetor bowls.


It sounds to me that either the fuel mixture needs to be leaned out or the passenger compartment needs to be sealed more tightly (exhaust pipes run to rear bumper?). Is this a steel car or fiberglass?

Now all of this having being said, early cannisters (metal) used a replacement filter and later cannisters are plastic throw away.
08-13-2007 10:49 AM
bentwings Hey thanks for the info. I'm going to do a layout of the system and make a Solidworks drawing. I can maybe post it so that it will be more clear.

I've seen this type of system so it is not my idea but I did not really paid attention to the details. Not enough disc space in my head. haha Sometimes streetrod stuff is not exactly correct but it works well enough for the limited amount of use we give them.

My thinking is that air will be continuously drawn in through the canister as fuel is used. When the car is shut off and simply waits for me to bring it to life again, the canister gathers fumes as required. Once the motor is started and begins to use fuel, air again comes into the canister, purging it.....hopefully.

I would think any dumping of vapors into the carb air cleaner could cause idle problems. A ported vacuum might work. My system will eventually have a blower and possibly an EFI injector so A/F ratio will be monitored. I would guess that fuel vapors dumped in will be accounted for by the o2 sensors. But I surely don't need random fuel vapors dumped in at idle, it's hard enough to keep a blown motor clean at idle. Consider also that this mess will be run on E-85. ($2.05/ gal today) I can probably tolerate some varance in mixture just as an alcohol motor can.

You know it is my younger days I would just roll the window down (hand crank not power) and say "gas fumes are just part of hot rodding, like noise, live with it." Today after 55+ years of sniffing gas and all the other hotrod fumes, I really long for a little cleaner air. haha Now if it was diesel fumes, it would be a different story. haha....yeah right a Willys with "stacks" ...I really don't wish to be banned from hotroding. haha

I'm going to the junk yard....back later.
08-13-2007 10:14 AM
Charcoal Canister

The reason the canister has to be purged is that after a while it will fill with vapors and will smell of gas. It's not a big deal to install one, you just buy a canister and a canister control valve and hook it all up. I'm having a difficult time picturing the rest of your set up and how it would work properly. There is a filter on the bottom of the charcoal canisters I'm familiar with. I'm not sure what you mean by running to it's own air filter. What happens is that when the purge valve opens fresh air is drawn into the canister through the bottom through the filter. That air mixes with the fuel vapors as they go into the engine. A check valve in the vapor vent line prevents pulling a vacuum in the fuel tank. The only problem I see is that the system I'm describing is an older GM one and you may not be able to get parts for it anymore. The newer ones are controlled by electric solinoids activated by the ECM. In any case I'm no instructor and sometimes don't explain things very well. I think the first thing you have to do is have a complete understanding about how the systems work then I'm sure you can design one easily enough.
08-13-2007 06:38 AM
bentwings Do these really need to be purged? Since I'm planning to use this on the vent line of the tank, air will come in thru the canister as well as trap fumes while the car is not running. This line will just have a air cleaner of its own attached to it....lawn mower type. The other line will go to the tank. Maybe I should use 2 vents on the tank. One would be used as described, the other would be a one way such as a check valve on a power brake unit. The check valve line would provide extra flow during high fuel full throttle. Under normal cruise the air coming into the tank would come in thru the canister. If it needs a little more, the air can come in thru the check valve. All venting going out of the tank however will go thru the canister. The check valve could also be an inverted tip over valve,..ball bearing type.

This isn't an emmission application except to prevent fumes from entering the car.
08-13-2007 04:56 AM
charcoal canister

The problem there is that the PCV valve is connected to manifold vacuum which means eventually the vapors would leak out where the throttle plate is. That's never a tight seal. The other thing is that the systems are designed so the fuel vapors don't get drawn into the engine until you're cruising down the road. There are so many variables with the amount of vapors that you'd have problems maintaining a consistant idle speed and quality start up after start up.
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