Fuel evaporation rate and vented tanks?

"My gasser has a sealed cap on the Moon tank and I plug the vent hose because the alky will evaporate in a couple days if I don't."


He doesn't say whether he hose-clamps his vent plug or not, but it sounds like he's just corking it to me.

I would think the sides of the gas tank would bulge before the pressure blew a hose-clamped rubber hose off, due to the differences in the pounds per square inch of the two. The sides of the tank have a lot more square inches than the sides of the rubber hose do. It would be like trying to raise the handle on a hydraulic jack by pushing down on the big cylinder. Although it can be done, it takes a lot of weight/pressure, because of the size differences of the two cylinders.

 

Take a can of paint thinner in a garage, it pops at different times during the day because expansion and contraction.
Tanks only need venting because of the fuel pump sucking them down.
NOT because of expansion.
Modern thinking should be counterintuitive, they made all these improvements to take the brain out of the driver seat and hook it directly to the engine.

 

Modern tanks have a one way valve to let air in on suction and keep vapors in on pressure. That's a simple one to solve and some caps do that also. Some high altitude OEM applications have a tank pressure control valve that prevents canister purge if the vehicle is not running.

Charcoal canisters are a filter on the vapor out line. Relieves pressure but retains the gas smell.
Just like any filter they are subject to wear out or become saturated. When was the last time anybody serviced a charcoal vapor canister? With a sealed air cleaner , there is also a hose that collects fuel bowl evaporation vapors into the canister. Most canisters have the vacuum operated valves attached. Thermostatic control valves control them and its a very simple system.
But its clutter on a hot rod engine.

 

Who's playing with this one?

 

I don't see this as particularly off topic. It is a real problem that many of us experience with this old Hot Rods and if it helps cure some problems it should be fair game. If it becomes all about emissions or being "Green" and is one step away from a freakin Prius, then it will probably, and rightly so, be closed down.
As for what i was talking about with an early type system, I was not advocating that it would help much with the evaporation, just that it gets rid of the raw gas smell.

That's rather personal isn't it

 

I still think that if you are getting rid of the raw gas smell, then you're also getting rid of the evaporation problem. Since what's evaporating is raw gas...if you don't smell anything, then probably nothing is evaporating.

 

OK.. since at least one mod has read this thread and it has not been closed down I assume it is alright.. However.. I am going on record as to questioning the "Hambability" (is that a word).

I have done a bit of research and discovered that we may be able to do what we are looking for without it being too intrusive and fairly easy.

I don't have much time today but I will make an update later this week with what I have discovered so far. If anyone else has ideas, I would suggest posting them and maybe we can all work together to come up with a HAMB friendly solution to the evaporation issue.

 

This is taken from Doug roe's "Rochester Carburetors" book.

Evaporative control system. ECS

This system reduces fuel vapor emissions that would otherwise vent to the atmosphere from the gasoline tank and carburetor bowl. The ECS is one emission control device that actually aids vehicle efficiency. Anytime raw fuel can be burned instead of polluting the air, economy and ecology are served. "



Our traditional cars don't run on traditional fuel , that's just a fact. Today's fuels evaporate faster and modern fuel systems are designed to work with this problem. No sane person would tolerate the waste and smell ( associated headaches, nausea, risk of health problems due to prolonged exposure of gasoline fumes) in a DD with a open, broken, malfunctioning EVAP system.

Letting it evaporate is the same as dumping it on the ground, wipe it up with a rag and then tossing the rag in the car.

 

Thank you. That is the answer I've been searching for.

 

This isn't a thread for you then is it.
No real need for your opinion here or to continue reading either.
Hit "unsubscribe" and find a thread that suites you and your concerns better. Perhaps one where your input would be helpful. Seems like you have lots to choose from.

 

You feel the comment that oldschool66 made is not relevant to this discussion. I don't see where your post helps anyone either.

 

Neither is yours.
Dave

 

previous 3 posts

you grumpy old men are funny!

 

I resemble that remark!!!!!!!

 

Seriously, I DO feel this topic applies to the HAMB. It has been pointed out already while this site is about traditional Rods and Customs but we cannot ever go back and get “traditional” gasoline to run in them anymore. Maybe we ought to be happy that the govt and fuel companies have not changed the recipe enough to not allow them to still be driven at all without suffering damage…

That being said, I really feel the fuel evaporation from the tanks can be improved. Time and testing will tell whether it is worth the cost and effort needed. At about $4.00 a gallon in the US right now, I guess that will be a personal decision we will all have to make. Personally, I plan on making an attempt at it but probably won’t be able to do any real world testing until next spring since the summer is just about gone now. Maybe someone in the desert southwest (Squirrel?) can get a system up and running sooner.

I have had some discussions with some folks that actually are responsible for these types of systems on modern OT cars. They answered some basic questions I had and taught me a few things that I didn’t know or was mis-informed about. Some of the take a ways I got from them were:

Obviously, the tank has to be sealed. Eliminating the vented cap and installing a modern sealed cap is pretty straight forward.

Old charcoal canisters are not very efficient. Just like anything else, manufacturers have learned from and improved their designs. In other words, don’t go to the junkyard and get an old ‘70s canister and expect great results. The newer the better. However, there are many different designs out there and I am looking into what design may be best for our type of application. Also, many are sensitive as to how they can be mounted in the vehicle (i.e. this end up). More to come on this.

Liquid fuel in a canister is a very big no-no. Modern fuel tanks have evap domes built into them that baffle liquid fuel from getting into the vent line. This might be one of the biggest hurdles in some traditional hot rod applications. There are liquid shut off check valves out there (haven’t looked for any yet) that can allow vapor to escape from the tank but not liquid. This may be the easy answer….

Canister sizing is kind of important. Very important in a modern vehicle due to the leak diagnosis part of the modern car requirements but still important to “us” because the canister is basically where the expansion takes place (i.e. cold fuel getting hot in a sealed gas can and expanding it). The canister has to be big enough to handle worst case pressure differential.

You still need to be able to allow fresh air into the tank to keep the tank from collapsing as you burn liquid fuel from the tank. This may or may not go hand in hand with whatever canister you decide to use.

Carbureted traditional engines can probably use a “key up” purge solenoid and never have any noticeable change in drivability (i.e. richer on engine start up when the canister is full of vapors). You need to purge the fuel vapors out of the canister or it will get saturated and stop working. One vacuum hose to the engine should not be a big deal to many traditional hot rods and customs.

As for the gas evaporation from the carb, I don’t see an easy solution to that. Personally, I can deal with losing a carb full of gas every once in a while if I can save everything in the tank. I don’t see any real way to stop that without creating an ugly mess under the hood. My hidden pump I already have rigged up seems to handle that issue fine.

I have just scratched the surface and plan on doing more research before I try to build my own system.

Currently, I am looking into some of the possible canisters, tank caps, purge solenoids, ect… to try to make a functioning system with reasonable cost and compatible parts. I can’t afford to damage a tank by expanding it or collapsing it so I want to make sure the system will work before I make it permanent. Fortunately, I just so happen to have a second fuel tank for my Olds that is damaged but does not leak. I plan on using it for my experiments and testing before trying it for real on the car. I’ll update later when I think I have a recipe of parts that are reasonably priced, readily available and seem to have a shot at fitting on a Traditional Hot Rod or Custom.

If we have any HAMB members that are industry experts, I know I would welcome their feedback on this subject. I do not claim to be an expert but feel I have a basic understanding of what I expect to happen when I hook this up. I am willing to spend some time and effort to try to make this work. I feel likely this evaporation issue will not go away and possibly get worse as the years roll on.

Comments and corrections are welcome.

 

I cheated. I only read the first and last pages here. But it answers what I was thinking too. My 55 Chevy has been sitting for some time in the garage. Son filled the new 16 1/2 gallon tank this spring and ran the 305 engine a few times. Car sat maybe a few months. Out of gas.
Added some that I had for the mower. I use nothing but the best cheap regular with corn juice in it. Drove about 5 miles and filled the tank. Drove another 5 miles to town then home. That's around 15 miles total. Worked on the engine a few times. Went out just before leaving for month vacation in July. Engine started right up. Ran few minutes and out of gas! WTF.
My kid does not live at home and is broke. He runs out all the time with his car. i didn't say, but figured he'd been taking the gas. Finally asked him and he swears he didn't. Evaporation? There is no puddle or spots under the car.
I have a 39 Ford with gas in it from late 70's. Probably would still start the SBC engine.
Not only are we paying more for crappy gas which lowers the MPG, we are losing much of it if we don't drive. But I could be wrong. I was once before.


Sent via homecomputer by a retard.

 

The stories are getting wild now 16 gallons in a month.

 

And yours

 

I've always been like this, I have just gotten better at it over the years.

 

keep the idea flowing, I would love to see where you go with this.

 

<TABLE border=0 cellSpacing=0 cellPadding=6 width="100%"><TBODY><TR><TD style="BORDER-BOTTOM: 1px inset; BORDER-LEFT: 1px inset; BORDER-TOP: 1px inset; BORDER-RIGHT: 1px inset" class=alt2>Originally Posted by 1964countrysedan
previous 3 posts

you grumpy old men are funny!
</TD></TR></TBODY></TABLE>I've always been like this, I have just gotten better at it over the years. There are so many more things to make us this way today. And we've had lots of practice.

 

Started looking at gas caps on my own OT stuff. Discovered that some of the sealed gas caps have a one way check valve built into them to allow fresh air in. That takes care of allowing fresh air into the tank without letting any out.

I am now thinking that I don't really need the charcoal canister at all. Just need a pressure relief valve that vents the tank to atmosphere if the pressure gets too high. Probably would be sealed most of the time anyway but would be able to vent excess tank pressure in case it happened to occur. Once the pressure relieved enough, it would seal back up. Just now need to determine what the pressure threshhold is for an old carb style tank using rubber hoses and hose clamps and find a check valve with that pressure setting.

I am now thinking I could do all of this right on the filler neck. Heck.. it would not be anything anyone would ever even notice. Hmmm.. It could be very simple.

 

BB,
I wondered about using a pair of small low press. checkvalves, one out, the other one in to allow pressure to drive either direction of venting?

 

I would classify that as a gas leak.

 

Takes 0.5 psi of vapor to make canister work.
Prior to 72 most caps vented to atmosphere @ 2 psi or less.
After 72 the pressures go up and tanks, straps, built accordingly.
Most all caps hold pressure and vent vacuum

 

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one thing to keep in mind as we think about this is the fuel feed line.

I think any pressure built up in the tank would be relieved by delivering fuel to the carb. It might be a vicious cycle allowing the carb to evaporate, and replentishing it.

Hmmm, maybe a fuel line valve/anti-theft arangement?

 

It sounds like you might really be onto something here! If it works out, take photos and post it during a tech week.

 

I don't know whether it's the case with all newer cars, but I have seen several that have both an inlet check valve AND a pressure relief valve. The pressure relief is set above the relief valve in the line to the canister and is there just for a safety back-up to prevent overpressure.

 

This is exactly what we need. Just adapt the cap and top of the neck to the existing neck. Any idea what year and model has something like this? Anyone willing to look at all their OT stuff and see if they have one already?

If we find one, we can probably zero in on a year or two and then start looking at different models that same year and find something easily adaptable to a variety of hot rod neck sizes.. I would say it needs to be for sure prior to 2001. Maybe even prior to 1996. Not sure if I can get to the boneyard to look around this weekend before they close..

 

My tank is quite a bit lower than the carb. Not sure how much pressure it would take to push through the mechanical fuel pump and up into the carb. I am guessing several PSI but we may be able to test that. Good thinking though...