Nitrogen and Fuel 1

[Dave21426]

I posted a question over in the auto fuel section but would like to know from the Chemical Engineers exactly what problems (if any) arise when intoducing air to gasoline vapors. The companies that make these testers have a warning against using air but I dont see the problem especially since all auto fuel system introduce air into the system for the purge feature, not to mention opening the fuel cap. Any thoughts"

http://www.vacutec.com/downloads/Ford-Rotunda_Smoke_Machines.pdf

 

[Latexman]

The problem is air and gasoline vapors can form an explosive mixture. Since the tester pressures the system and this potential explosive mixture may leak out and the tester is not built for an explosive atmosphere, it may go . . . BOOM!

Good luck,
Latexman

 

[Dave21426]

"air and gasoline vapors can form an explosive mixture"....Really? I guess that was the day I slept in my college chemistry glass. "Air" is not only in an auto fuel system but fresh air is introduced via the purge valve not to mention the fuel cap and fuel changes. I have a coleman lantern that uses gasoline. You "pump" up the system and pressurize it (air is in the tank too) and guess what, it has never exploded in 60 years.

 

[Latexman]

You just confirmed (to me anyway), why Ford's Engineers added a small PSA N2 generator to this fuel emmission leak tester.

Good luck,
Latexman

 

[Dave21426]

Ford Engineers are just on edge after the pinto incident and F-150's that blow up.

 

[Dave21426]

This company uses compressed air in their smoke systems. Guess its not a problem.

http://www.youtube.com/watch?feature=player_embedded&v=ztKF5Xz5dWk

 

[Latexman]

It's not a problem, until the leak testing produces a flammable mixture escaping via the leak and the mixture finds an ignition source. Then, it's a big problem, especially if it's you doing the testing.

There are a gazillion factors that come into play, like how volatile is the flammable liquid, the temperature of the liquid, how big is the leak, is it indoors or outdoors, which way is the wind blowing and how fast, where is the ignition source, is anyone in harms way, did they leave the tester running during break/lunch, etc., etc.

Most of the uncertainty is eliminated by using N2. The Ford tester is superior from a safety standpoint. It's probably more expensive too.

It's obvious your mind is made up, so why keep bringing it up?

Good luck,
Latexman

 

[ChEMatt]

Latexman's first response was correct considering you are in the 'chemical engineering' forum. Star for you, Latexman.

That is the main issue as far as chemical compatibility goes: air + gas vapors = explosive mixture and shop environments generally are not Class 1 Div 1 or 2 rated. I'm trying to think if getting air into another pressurized system might result in corrosion or some material compatibility issue, but nothing comes to mind. Perhaps compressing air could result in a bit of water condensation which may be undesirable, but that's a bit of a stretch considering the very low pressures these are producing.

I'd suggest calling each vendor and asking why one can use air on a fuel system pressure test, and ask the other why the do NOT use air on a fuel system pressure test.

Onwards,

Matt

 

[Dave21426]

Matt, I emailed those companies and they have not replied. Guess they dont want to be locked into that question. The emission system is (fuel system) has air and fumes all the time. When it purges it introduces AIR into the system. Any ignition source, smoker or not will create a bomb. Emission system pull a vacuum to check for leaks and then report to the ECU. I wonder how dangerous it would be to to pull a vacuum on the system and monitor it for leaks. Not sure if fumes thru a vacuum pump pose a problem. I think it would have to be a parastaltic pump. Dont have my mind made up, just want scientific answers, hence this forum.

 

[25362]

If the subject of flammable mixtures is of interest, visit thread798-33615.

 

[Latexman]

Using an inert gas is not without it's problems to consider too. Asphyxiation. The big unit says it uses a 2 minute test. That will limit, not eliminate, asphyxiation scenarios. The small unit(s) do not mention a time limit.

Good luck,
Latexman

 

[Dave21426]

That is an interesting thread. Still with the use of nitrogen you have to air somewhere in the system to create the smoke, an element to ignite the mineral oil(which to me is the actual danger). Asphyxiation in a ventilated shop environment would never happen. If you were in the car with the doors closed and opened up a welding tank of inert gas then yes.