Fuel Tank Venting

Pat

Supporter
With the new fuel cell installation, I'm converting to a non-vented filler cap. So I would appreciate any suggestions as to the ideal fuel tank venting system. I've seen several different approaches:
-Lines from the tank/cell to the carb air cleaner. (What happens if you ever backfire through the carb?)
- A breather line from the tank to the rear of the car exiting below the frame (seems like it would ingest water/dirt driving in foul weather).
-Some cars at local events have a rather elegant looking aluminum bottle with an air filter on it but I'm not too keen on the firewall mountings I saw. Seems to me you need to vent outside of the body of the car.
-I've looked at a carbon canister such as a production car but those require a vacuum system to purge them which is a little more complex than my engineering skills.

Any suggestions?
 
Pat.
I thought long and hard about the problems you mention. You mention a fuel cell. Is or are they still in the the regular location on the sides of the car?? or have you put it in a different location? If still on the sides then this information will be of some help, or at least to get your thought processes working. I also have non vented filler caps. I vented both tanks to the front of the car and exited at the location of the filler tubes using a marine type vent mounted just to the rear of the main fillers. I vented both the rear and the front of the tanks and joined them into one line to the filler locations. I installed a rollover valve in each after they were joined at the front. The ones I installed have a slight amount of pressure required to actually vent in both directions. The roll over valves I used, I believe came from Demon Tweaks(sp?) and were not cheap.

P9060282.jpg


The reason you need to vent both ends of the tank is because if you park nose down on a slight hill, and you are vented only in the front, the air bubble that will form in the rear of the tank will expand with any heat and force the fuel right up the vent line. This will force the fuel out of the tank and into the front compartment. If you have a roll over valve it may not work as the tank is right side up and the weighted ball won't rise with the fuel to close the line off. The connected vent lines allow for the movement of air between the front and rear of the tanks, as well as in and out of the tanks, thus negating any rise in pressure.
You didn't mention also whether you have one or two cells. If you are using two you might want to think about how you read empty and full in the tanks. If you have a switch that changes the reading to the tank selected, you will be OK as long as you know for sure there is fuel in both tanks. Don't you just hate it when you change over and the other tank is empty?? I use one tank for the tank measurement and have a crossover line from the left tank to the right. This winter I plan to change it over to a larger line. There isn't enough flow from the left to the right while driving to notice. Drove to a car show and was going to fill up when I left. When I got back into the car several hours later, the tank was more than 3/4 full instead of nearly empty.

Bill
 
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Pat get yourself a charcoal canister from a wrecking yard and put the vent lines into it.
I would bring these from the filler necks as it is the highest place.
You have an exit hose on the canister, vent that into the induction system.
In the exit hose use a purge solenoid that operates when the ign is switched on

My canister is in the pontoon area at the rear ,you wouldn't know it was their.

Look in a workshop manual they are all the same.

Jim
 

Pat

Supporter
Thanks all. Bill, your picture is most helpful. I've ordered a small check valve similar to what you have pictured for the front.
In answer to your question, I have two new cells going in each side sponson/pontoon area of the car. They will have a small "burp" vent in the first cell access plate as well as a primary vent in the rear of the cell. All porting, including the filler neck have check valves. The cell plumbing is actually pretty easy as I have -6AN lines exiting the rear of each cell and one forward -4AN line. I'll mount a marine valve similar to what you've posted for the forward line. My issue is to find out what to do with the primary vent lines exiting the rear of the cell as I'd prefer not to route those lines all the way to the front of the cell.
Thanks Jim. I've looked at several canisters and they all seem to have a confusing array of multiple lines and ports. I'll see if I can find a manual I can decipher. The ones I've seen call for an expansion chamber plumbed to a restrictor to an evaporation chamber then to the canister and purge fan. That's a little more complexity than I'd like given the limited space.

When I look at units similar to the Toyota canister below I realize I'm not the brightest tool in the shed but my wife thinks I'm charming ;)
 

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Pat
Make sure your rear vent lines are higher than your fuel filler cap.
If you over fill that tank, or at least fill it up to the base of the cap. The fuel will syphon out of the vent line.
I have mine running up the rear bulkhead (above fuel cap level) and back down again into a charcoal canister located in the rear sill area.
It only has three ports, tank (pipe form tank), vent (overboard vent), purge (pipe to induction via a solenoid valve)

Clayton
 
Pat, one of my rear vents is pictured here. I positioned the valve on the tank beside the gauge, to I could get a hold on the internal nut to tighten.
The vent pipe comes through the horizontal panel and up the back of the 'A' frame and is terminated at about the height of the water vessel, I may put some charcoal canisters on at some point. I'll post some pix tonight. K
 

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