Fuel Tanks

[Engineer]

Originally posted by: Evadman

Originally posted by: Jahee
No i was just wondering where they put it mostly... and whether it was a vent or a valve or what.

Like I said, there is a vent right under the cap. There can also be a rollover valve that prevents fuel leakage in a rollover.

We make the rollover valves also. Have to leak test them just like anything else.

As for the vent under the cap, I know that the cap is rated for 10 psi and will actually release pressure at that level (that's why we test them at extremely low pressures). I do not know if it will let in air pressure if the pressure is low enough or if it matters. Gasoline will vaporize easily and fill any vacuum void left. Just to throw a kicker in, we also have the fuel gauge level sensors and they are "OPEN ELECTRIC" in the tank. I don't think that I would want AIR getting to open electric fuel level sensors!

 

[Jahee]

Originally posted by: Engineer

Originally posted by: Jahee

Originally posted by: Engineer

Originally posted by: Evadman
Fuel tanks are made of thin sheet metal. Thin sheet metal is porus to air, but not to long hydrocarbons. The long chain hydrocarbons (20+ atoms) get stuck when trying to exit through the crystaline structure of the sheet. Most molecules in the air are made up of 2 or 3 atoms, so they can migrate though the crystaline structure. That is why you need to be careful when you are filling your tank, sometimes you can put gas int he tank faster than the air can get out through the walls. Then you end up spraying fuel out the end of the filler neck. Same reason you are not supposed to leave your car running; new cars hae a fuel return to the tank, so you will be filling fuel from the nozzle and from the fuel return which can build up pressure and push the fuel nozzle out of the car leading to a fire hazzard.

Our gas tanks are made from 7 layer plastic blow molding. No metal. The inner layer has to be virgin plastic (new). The outer 6 layers can be recycled.

Thats interesting, how come 7 layers?

To be honest, I don't know. I would guess that it has something to do with emissions. Lev II emissions went into effect over the last few years. I'm hoping that I never see Lev III (assuming it exists) because the leak tester requirements are a pain in my butt (since I help design and program the machinery around them).

When you say emissions, do you mean of hydrocarbons out of the tank, is it that big of an issue?

 

[Engineer]

Originally posted by: Jahee

Originally posted by: Engineer

Originally posted by: Jahee

Originally posted by: Engineer

Originally posted by: Evadman
Fuel tanks are made of thin sheet metal. Thin sheet metal is porus to air, but not to long hydrocarbons. The long chain hydrocarbons (20+ atoms) get stuck when trying to exit through the crystaline structure of the sheet. Most molecules in the air are made up of 2 or 3 atoms, so they can migrate though the crystaline structure. That is why you need to be careful when you are filling your tank, sometimes you can put gas int he tank faster than the air can get out through the walls. Then you end up spraying fuel out the end of the filler neck. Same reason you are not supposed to leave your car running; new cars hae a fuel return to the tank, so you will be filling fuel from the nozzle and from the fuel return which can build up pressure and push the fuel nozzle out of the car leading to a fire hazzard.

Our gas tanks are made from 7 layer plastic blow molding. No metal. The inner layer has to be virgin plastic (new). The outer 6 layers can be recycled.

Thats interesting, how come 7 layers?

To be honest, I don't know. I would guess that it has something to do with emissions. Lev II emissions went into effect over the last few years. I'm hoping that I never see Lev III (assuming it exists) because the leak tester requirements are a pain in my butt (since I help design and program the machinery around them).

When you say emissions, do you mean of hydrocarbons out of the tank, is it that big of an issue?

It's an issue with the EPA. The automakers actually take your product, place it in a special testing chamber and fill the product with gasoline. They then measure the emission of gasoline from the product. The limits are very small. So yes, it's a big issue. We spend millions on leak testers for those products.

 

[Evadman]

Originally posted by: Engineer
As for the vent under the cap, I know that the cap is rated for 10 psi and will actually release pressure at that level (that's why we test them at extremely low pressures). I do not know if it will let in air pressure if the pressure is low enough.

The gas cap is not supposed to let any air in, the charchol chanaster acts as the fuel systems vent. That way any gas fules are not releasted tot he atmosphere, they are stored in the canister and burned later. The charchol canister is that big plastic canister about the size of a coffee can in the engine compartment.

 

[Howard]

Originally posted by: Jahee

Originally posted by: Evadman
Check your sarcasm meter batteries Engineer

Haha! I was going to say, last time i checked metal does'nt have a crystalline structure

Did you ever check?

 

[Jeff7]

Originally posted by: Engineer

Soda does not evaporate like gasoline does.

Good point.
Is it volatile enough to fill a void left by consumption of the gasoline? (Hypothetically speaking, ignoring the vent.)

 

[imported_Baloo]

The filler tube has nothing to seal it - it double as a vent.