Fuel Tanks

[Jahee]

When the fuel is used in the tank, the level drops so if there is nowhere for air to enter the tank, a vacuum would be created and you'd get to a point where the fuel pump can't pump the fuel anymore.

How do manufacturers get around this? i'd guess some kind of valve or something but where would it be located?

 

[d33pt]

there's a vent that goes to your filler hole. If you look carefully you'll see it.

 

[Inspector Jihad]

i think the drop in air pressure created by the removal of the fuel is insignificant.


but i'm not really sure.

 

[Engineer]

Originally posted by: d33pt
there's a vent that goes to your filler hole. If you look carefully you'll see it.

That tube is contained under the filler cap. (My company makes filler pipes).


I'm not sure either. My company (different division) also makes gas tanks and fuel pumps. Maybe I'll try to ask someone Monday. I'm not so sure that the gas fumes wouldn't just take the place of the vacuum anyway as gasoline evaporates rather quickly in open air.

I know that diesel tanks have vent lines (with a filter on top). I have programmed machinery to assemble the filter tube.

 

[Howard]

Originally posted by: Inspector Jihad
i think the drop in air pressure created by the removal of the fuel is insignificant.


but i'm not really sure.

Depends on how much gas fills the tank when it's full. There would have to be a lot of wasted space in order for the drop in pressure to be insigificant.

Besides, if the air wasn't replaced, it would be nearly impossible to remove the gas cap.

 

[Jahee]

Originally posted by: Engineer

Originally posted by: d33pt
there's a vent that goes to your filler hole. If you look carefully you'll see it.

That tube is contained under the filler cap. (My company makes filler pipes).


I'm not sure either. My company (different division) also makes gas tanks and fuel pumps. Maybe I'll try to ask someone Monday. I'm not so sure that the gas fumes wouldn't just take the place of the vacuum anyway as gasoline evaporates rather quickly in open air.

There'd have to be alot of fumes, if this is true what about diesel engines, there arent as much fumes produced from diesel...?

 

[Engineer]

Originally posted by: Jahee

Originally posted by: Engineer

Originally posted by: d33pt
there's a vent that goes to your filler hole. If you look carefully you'll see it.

That tube is contained under the filler cap. (My company makes filler pipes).


I'm not sure either. My company (different division) also makes gas tanks and fuel pumps. Maybe I'll try to ask someone Monday. I'm not so sure that the gas fumes wouldn't just take the place of the vacuum anyway as gasoline evaporates rather quickly in open air.

There'd have to be alot of fumes, if this is true what about diesel engines, there arent as much fumes produced from diesel...?

See edit above about Diesel. There is a tube with filter to open air on those. Emissions from diesel are indeed small. Gasoline however, is very volitile and expands tremendously.


By the way, we test our gas tanks using helium while the tank is in a vacuum chamber. A helium sniffer checks the vacuum lines for helium leaking from the tank. The emissions requirements are tremendous.

 

[Jeff7]

Originally posted by: Inspector Jihad
i think the drop in air pressure created by the removal of the fuel is insignificant.


but i'm not really sure.

I'd say it's quite significant. Get a bottle of soda, turn it upside down, and start sucking soda out without letting more air in. The bottle will start to be crushed by external air pressure very quickly, and if you do it enough, you'll start to blow out blood vessels on your tongue and lips.

Fill up a container halfway with liquid, and let air in the other half. Now extract the liquid. Suddenly the pressure has been cut in half. I'd call that significant.
Example of what air pressure can do

 

[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.

 

[Engineer]

Originally posted by: Jeff7

Originally posted by: Inspector Jihad
i think the drop in air pressure created by the removal of the fuel is insignificant.


but i'm not really sure.

I'd say it's quite significant. Get a bottle of soda, turn it upside down, and start sucking soda out without letting more air in. The bottle will start to be crushed by external air pressure very quickly, and if you do it enough, you'll start to blow out blood vessels on your tongue and lips.

Fill up a container halfway with liquid, and let air in the other half. Now extract the liquid. Suddenly the pressure has been cut in half. I'd call that significant.
Example of what air pressure can do

Soda does not evaporate like gasoline does.

 

[StormRider]

I heard it operates in the same way the vagina does to prevent air from getting in when you're pumping...

 

[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.

 

[Evadman]

Check your sarcasm meter batteries Engineer

 

[Engineer]

Originally posted by: Evadman
Check your sarcasm meter batteries Engineer

oops. I didn't read the entire post...I stopped at the metal part!



Watching NC State vs NC. Hoping State kicks their butt!

 

[91TTZ]

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.

Hmmm

 

[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 and petrol isnt 20+ atoms long. haha

 

[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?

 

[Evadman]

Seriously though, there is a vent in the filler neck right under the cap. In addition, your gas tank (in newer cars) has a vacuum pulled on it to prevent polution. That is why when you get your car smog tested they take the cap off and test the cap. The pump is more than powerful enough to overcome this vacuum.

 

[91TTZ]

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

Yes it does.

http://en.wikipedia.org/wiki/Crystal

"Almost all metal exists in a polycrystalline state; amorphous or single-crystal metals must be produced synthetically, often with great difficulty."

 

[WHAMPOM]

Most probably through the vent. ?????? LOL Did you think they made a fuel tank without one?

 

[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).

 

[Jahee]

Originally posted by: WHAMPOM
Most probably through the vent. ?????? LOL Did you think they made a fuel tank without one?

No i was just wondering where they put it mostly... and whether it was a valve or vent or what.

 

[Engineer]

Originally posted by: WHAMPOM
Most probably through the vent. ?????? LOL Did you think they made a fuel tank without one?

I highly doubt that. Considering the leak test requirements on the tank and supporting fuel system (helium leak test under vacuum chamber). There would be no point to such strenuous leak testing if there were simply a vent in the tank. Hell, we are looking at blow molding the fuel pump right into the tank to reduce emissions (vs locking it in from the outside).

 

[Jahee]

Originally posted by: 91TTZ

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

Yes it does.

You know you're right actually, i dont know what im getting confused with

Just read that article to double check actually

 

[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 Engineer and I said, there is a vent right under the cap, but the vent is still sealed against the cap. The fuel pump can easily overcome the vacuum created. There can also be a rollover valve that prevents fuel leakage in a rollover.

Originally posted by: Jahee
Haha! I was going to say, last time i checked metal does'nt have a crystalline structure and petrol isnt 20+ atoms long. haha

Sure it does. I try to make my sarcasm posts as true as possible while spouting pure bullsh!t.