Need to vent, my gas tank

Chuck Moreland · 07-28-2003, 11:28 PM

'73 project car. I need to vent the gas tank.

The factory vapor recovery system has been sacrificed on the alter of weight reduction.

I need a vent that will not allow fuel to escape when sloshing about or even in a rollover.

I have a hose fitting on the tank and another at the filler neck, either could be used.

Suggestions?

Tyson Schmidt · 07-28-2003, 11:37 PM

You'll have to connect the two, or fill-ups could get interesting! Then you need to T off of them and run it to an expansion tank that vents to the outside of the car.

Put a one-way check valve on the hose coming from the T that goes to the expansion tank that will allow air to be drawn into the fuel tank, but won't let fuel spill out.

I kept the factory set-up on my car, and even bought a brand new charcoal cannister from the Dealer. It doesn't weigh much, is environmentally consciuos, and avoids venting issues, spillage issues, and fuel vapor odor issues. O.K., so I'm a bit of a tree-hugger.

scottb · 06:04 AM

Chuck: I had to sacrifice my vapor recovery tank when I installed my auxillary a/c condenser/fan set-up. I'm in the midst of the installation. Here's what I plan to use to replace the vapor recovery tank:

It's smaller than the factory tank, but should do the job. What the picture doesn't show is the fitting hole on the end. I'll use two of the three holes, and plug the other. I've been told that the vacuum hose must be lower than the hose from the fuel tank. So, I'll mount the vapor recovery tank vertically (or nearly so), and vacuum from the fitting on the end while filling from one of the fittings on the side.

Scott

Chuck Moreland · 07-29-2003, 07:58 AM

Where can I get a check valve?

BGCarrera32 · 07-29-2003, 08:49 AM

McMaster has some mini polypro spring loaded ball check valves.
search "check valves" and then click "miniature check valves", page 2.

-BG

BGCarrera32 · 07-29-2003, 08:55 AM

Which also makes me wonder, how do they vent a fuel cell? Or don't they...

RallyJon · 07-29-2003, 08:58 AM

Fuel Smell/Expansion Tank

HarryD · 07-29-2003, 01:07 PM

Quote:

Originally posted by BGCarrera32
McMaster has some mini polypro spring loaded ball check valves.
search "check valves" and then click "miniature check valves", page 2.

-BG

Be very careful with these check valves. They can overpressure your tank. If you insist on using a device like this, remove the spring and orient it so that gravity keeps it closed.

surflvr911sc · surflvr911sc's Garage

Chuck, do you have any way to hook an evap tank up to vacuum? That would eliminate the need for any check valves and you wouldn’t need to worry about venting to the ground.

Chuck Moreland · 08-02-2003, 08:37 AM

I'm looking for some feedback here.

This is the current plan:

The check valve allows air into the tank, but nothing to escape. This should be safe in a rollover.

It appears the fuel cap can prevent overpressure in the tank. The seal is spring loaded.

I have seen products that flow in both directions, but close off due to gravity in a rollover. However I fear those products may not close off if the car rolls on its side.

Tyson,

You suggest an expansion tank. I don't understand how that would work or help. If it is vented, how does that prevent fuel spillage? If it has a check valve, why do I need a tank?

Tyson Schmidt · 08-02-2003, 12:03 PM

The expansion tank isn't really necessary if you use the check valve, but it does add that extra measure of protection. The tank gives the fuel a place settle, and the vent is at the top of the tank, so it's essentially just a back-up.

The other type of expansion tank, (the factory set-up had both) is placed in the highest place possible,(under the dash) and is there to allow the fuel vapor to accumulate and condense back into fuel droplets and run back into the tank. This essentially keeps you from getting really bad fuel mileage while your car just sits there! It helps keep the fuel in the tank. You don't really need this one either.

Chuck Moreland · 08-02-2003, 02:29 PM

So you think my drawing will work?

What about overpressure in the tank, will the spring cap relieve this safely?

Tyson Schmidt · 08-02-2003, 03:46 PM

Yes, and also if you use a stock check valve, it allows minor pressure to freely escape, but if it gets a large volume quickly, or fuel pushing against it, it shuts off.

randywebb · 03-25-2006, 11:41 AM

Reviving this thread...

Chuck did you ever implement this? If so, did you follow your diagram above and what parts did you use? And... how well does it work? Thx!

I'm asking b/c I discovered that my left fender exp. tank is trashed and it costs $70 (!)

stlrj · 03-26-2006, 05:58 AM

On all cars today, a check valve is built into the gas cap. As part of the smog check, it is removed and pressure tested to hold pressure but allow air inside to prevent a vacuum from forming inside the tank.

Joe

75Carrera · 75Carrera's Garage

For those who may still have the original stock canister; 1. Have you ever serviced the thing? 2. How much charcoal is it supposed to hold? (To fill it up would weigh a ton)