Discussion in '1947-1954' started by Bilbo, Dec 1, 2014.
Bill, I could tell some horror stories on this subject, but, better not...
Fuel Tank Overflow Expansion Tank
Why couldn't a fella set up the fuel tank just like a radiator? You would add a vent line (inside the cab) to the gas filler neck and run it to an expansion tank (mounted beside the gas tank).
Fill the truck up with gas and place the non vented gas cap on. When the gas expands it will flow into the expansion tank (and not down the outside of the truck). When the engine is running it will then pull a vacuum and suck the gas out of the expansion tank. When the expansion tank is empty it will operate simply as a vent.
The volume of the expansion tank would be based on the capacity of the fuel tank and the maximum temperature rise for the geographic location of the truck.
Sounds logical to me... what say ye?
The roll over vent valve my own self .
My rig ? I'd prolly just add an open vent tube right close to the top of the filler neck and run it outside the cab so mud dauber wasps could screw it up and kill me .
I'd love to hear some stories Steve , i never shy away from horror stories when it comes to old vehicle safety .
Seems like the gas fumes would deter any living insect from setting up home in a gas tank vent line? But if you are concerned about something getting into it go to your local tractor supply, head for the hydraulic area (log splitter parts), and buy a sintered bronze vent fitting for the open end of the hose. I have one on my ole crate.
Google up evap and the yellow sac spider. They love to nest in evap canister vent lines which will turn on the check engine light for a restricted vent. Common enough in Mazda's to create a recall, but has been seen by multiple manufacturers. Maybe they enjoy the alcohol fumes?
Pretty good concept, Roadster. I wonder what effect having to pull negative pressure on the fuel tank will have on engine performance? I also wonder if the unvented fuel caps will work on our filler neck? (That, I can find out at my FLAPS). Looks like the recovery tank would need to be mounted as high as practical, to allow the fuel return with minimal vacuum?
My original idea was to keep the vented gas cap, and install a vent tube high enough up the filler neck that the gas pump nozzle will insert past the vent tube. Then run a steel line inside the cab, and out the floor at the back, including either a screen or sintered metal fitting on the end of the vent. Can you all see any particular problems with this plan? BTW, Roadster, since you're an engineer, would the new vent fitting in the filler neck have to be welded instead of brazed, since it's inside the cab? In industry, if a fire can cause failure of a part to increase fuel to the fire, that part cannot be made of plastic, brass, or copper. I'm not real familiar with all those rules, but when it came to solenoid valve bodies, I always had to consider that.
Without the expansion tank, the issue I see is gas running out under the truck. Depending on where the truck is sitting (like in your garage) that can be a big hazard. The more I thought of this the more I was concerned about it. That's what prompted me to dig deeper and post the expansion tank sketch.
Brass vs. Steel fittings: I don't know the answer from a DOT perspective. By the time the fire gets hot enough inside your truck to effect the soldered joint or the brass fitting, the temperatures will have far exceed the flash point for gasoline, thus bad stuff will have already happened.
Your stock fuel pump should have no problem dealing with the minimal vacuum (less than 1 psi) it takes to evacuate the fuel in the expansion tank. Keep in mind the only time it will see this vacuum is if there is gas in the expansion tank. As soon as the fuel pump starts pulling the fuel out of the tank the slight vacuum in the fuel tank will suck the gas out of the expansion tank.
Location of the expansion tank would be beside the stock tank, low enough that the fuel can gravity flow into it when the fuel expansion in the fuel tank occurs.
http://www.jm-metaljoining.com/pdfs/Silver Brazing Alloys and Fluxes.pdf
Thanks for the feedback! I'm liking your idea more now. Appreciate the perspective of someone whose analytical skills have been honed better than mine! I expect to carry through with your plan, but it will be a few weeks. I'll keep photos and updates when I get moving on it.
How big of an expansion tank?
18 gallon fuel tank, tank full of gas
50 degree F gasoline at fill (underground storage tank)
120 degree F inside cab (summer time)
The volume increase will be 0.67 gallons
That's a lot of expansion!
Assuming a 1 gallon capacity expansion tank built from 4" pipe it would need to be about 18-1/4" inside length.
Bilbo... could you take some photos of your existing filler neck inside the cab? Curious how much space you have and what the stock filler neck configuration looks like.
Looking forward to you making this become a reality.
Spiders! Gas-sniffing arachnids invade fuel lines
Thanks John1, I followed your lead and found this article. Amazing this little dudes can live in a gasoline vent line. He does look a little "buzzed" Very interesting... http://www.techhive.com/article/214...es-force-a-software-fix-for-mazda-sedans.html
Thanks for the info. I found a picture from assembly. Looks like the overflow tank will need to be mounted so that the 'air space' above the vent tube will be above the point where the overflow tube connects to the filler neck?
How about a sketch...
Looks like there is plenty of room there for some additional tubing and the expansion tank.
As for the port location on the filler neck, I am thinking this would be the ideal set-up:
But if you had a non vented filler cap that you were absolutely certain didn't leak you could merely splice into the vent line, maybe even simply put a tee in the rubber hose that's already in the vent line and that would feed the expansion tank.
Hope this makes sense.
Thanks again for the follow up. Very helpful! The existing filler neck has an internal 'tube' that extends past the point of the vent attachment, so that may help with the design. I'll have to get a measurement as to how far it actually extends down the neck.
My Question :
Why wouldn't you add the vent pipe bung to the top surface ? .
It's be raised up higher and so less likely to allow liquid fuel from getting into the vent pipe on turns .
Just wondering .
Hey Nate, the side port isn't the vent port, it's the port that goes to the expansion tank. When the gas expands it runs into the side port and the gas flows into the expansion port.
The vent port is a separate port.
I think it would be best to keep the liquid level below the filler cap, even with a non vented cap, if at all possible.
Well John ;
I have worked on many pollution controlled vehicles and they all have the port on the upper side of the pipe for the reason I mentioned ~ once the vapor separator gets soggy , you're kinda done there .
Maybe it's because I drive my oldies too fast , I know how the fuel loves to slosh up the filer pipe .
You ole canyon carving Hot Rodder
Put it on the top... I'm ok with that. But if it is too high and the filler cap doesn't seal liquid tight, fuel will be running down the side of the truck again.
Vent Pipe Bung
Just so ;
I wasn't meaning to put it against the cap , but only 1" or so below that .
I'm not sure if I'm a Hot Rodder or just a damnfool who enjoys rapid motorvation .
Ditto! I'm assuming your using a vented cap also.
Fuel Tank Venting
Well Robert ;
If you add a fill pipe vent , you wil no longer need the vented gas cap....
The systems went to closed in 1971 (IIRC) in order to try and capture the hydrocarbons that naturally evaporate from fuel tanks .
Simply duplicating the top fitment bung and running a vent hose up then down and out , should allow the use of a non vented cap and no more ruined paint .
I need to look into where a TSS is in So. Cal. as that vent hose end looks pretty dang slick to me .
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