Smoke tester

[Dave21426]

I have noticed that some emission control smoke testers warn against using a supplied air source to test for leaks within the fuel system. They are afraid that the oxygen, as low as it is in air, with ignite some how with the fuel and blow up the car. They recommend an inert gas like argon. But lets see, in a modern emission control system the ccv valve opens up to to allow AIR to enter in the system to evenetualy purge into the intake. Not to mention, isn't air composed of 78% intert nitrogen.

 

[dicer]

And then the time arrives when you want to go to a gas station and open the dreaded fuel cap and let lots of air into
the tank. Especially on all those old airplanes with recip engines, there is no saftey valve that is keeping all that air out of an aircraft fuel tank. And besides what is that funny stuff that goes spuhhhhh when you losen that gas cap at the station?
Must be argon huh???? I'm sure glad they never put a "vent" to let air in a gas tank in the old days. Yeah I'm being funny.

 

[berkshire]

dicer,
Did you ever notice the effect on the engine when a bug plugged up that "nasty" air intake?
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[Dave21426]

I wonder if you could close the purge valves and let the car pull a vacuum on the emission system then monitor it with a vacuum gauge. Seems simple and safe.

 

[patprimmer]

Compressed air is a lot more reactive than ambient air I think.

Certainly pulling a vacuum seems safer and effective.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

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[ivymike]

Hmm, I always thought that gas tanks were full of gasoline and gasoline vapor, and that even if you left the cap off there would not be a flammable mixture except on extremely cold days? Seems like pumping air into the tank would ensure the presence of a flammable mixture at least at the point of introduction?

 

[ivymike]

Separately, is the ccv valve not for crankcase ventilation? What does that have to do with the fuel system?

 

[Dave21426]

The original question pertains to the emission control system. The closed Canister Valve is part of that system along with fuel and fuel vapors. When you put a smoke tester into the CCV valve or anywhere in the emission system..... then open the FUEL tank cap, what do you think will come out?

 

[ivymike]

it sounds like you're saying that the smoke tester manufacturers would recommend that a mixture of Argon and gasoline vapors is what comes out, and you want to know why mixing air with gasoline vapors would be bad?

 

[Dave21426]

In a round about way yes. They want to use nitrogen (some manufaturers). 1st Air is 78% nitrogen 2. if you are buring mineral oil to get smoke you must need air for combustion 3. Gas and air are mixed together in an auto fuel system via the CCV all the time.

 

[ivymike]

You sure about that last part?

Soooo... air is 78% nitrogen, which means it won't sustain combustion? For some reason I thought air was a more effective oxidizer than pure nitrogen by a large margin?

 

[Dave21426]

The CCV is normally open, ie car off, it vents to air. Car started it closes and creates a vacuum in the system. When the system purges it needs to open to release the vacuum, like the vent on your gas can or pool chlorine jug.
Quick education:

http://www.autoshop101.com/forms/Hybrid13.pdf

I dont think it would create a sustainable combustion but there are alot of factors like its now under about 14 lbs of pressure from the smoker air source. Hence my question here.

 

[ivymike]

Ahhh... so by "auto" fuel system you meant "pre-2010 Prius" fuel system? That PDF was informative...but now I'm wondering where you plan to stick the pressurized air? If you put it into the outer tank to find a leak in the outer tank itself, I expect you'll force liquid fuel into the canister and it will eventually migrate to the outer tank, necessitating replacement (as per the PDF). Were you going to inflate the inner bladder with air? That sounds like a fire hazard to me.

 

[Dave21426]

Bladder, what are you talking about here. Smokers inject smoke into the emission service ports (usually under the hood of the car).

 

[ivymike]

did you read the PDF you linked to? Are the ports you're talking about not connected to lines that connect to the fuel tank?

 

[Dave21426]

Thats a generic diagram, hence where you are getting the term bladder but if you look at page 3-13 do you see where fresh air is coming in thru the tank and out thru the intake. My car has the CCV in another place. Different manufactures call it different things. Regardless, its fresh air into the tank. But another point is how would a SMOKER, smoke with an intert gas alone.

 

[Dave21426]

Ok that PDF is for a hybrid, hence the bladder. Depending on the purge conditions they may not go thru the tank, just the canister, what is your point?

 

[ivymike]

you're misreading the diagram- that's not what's happening. page 3-13 shows a leak check wherein air is drawn through the outer tank, which is not intended to contain fuel, to see if fuel vapors are detected. The main bladder of fuel does not have air drawn through it. The car does that automatically on a regular basis (on every startup?), so if a leak as started it will hopefully not have leaked much by then. Also, this is air being drawn (by vacuum) through the enclosed area, and the result would be much different if you forced compressed air into the same volume (you'd squeeze the fuel bladder, for one).

I can't cite the configuration of every car in existence off of the top of my head, but the ones I've looked at do not draw air into the tank intentionally as part of testing for leaks - the closest they do is draw a slight vacuum and monitor the recovery rate.

I thought a smoker worked by boiling mineral oil and mixing it with a cool gas to condense and disperse the resulting vapor, not by burning the oil? That process would create "oil fog" rather than "smoke" and would not rely on the presence of oxygen.

If you feed "smoke" into the intake manifold and it manages to waft into an evaporative emissions control line to reveal a leak, no problem. I would not recommend connecting those lines directly to compressed air to force air + oil fog into the evap system.

 

[Dave21426]

Forget the diagram I sent you with the bladder, its a hybrid. Regardless, if the intake purges the fumes you have to have a vent. On my car that valve is in the air cleaner and brings fresh air thru the evap system. All smokers pressurize the evap system.
read the manual I attached.
Also watch the video:

https://www.youtube.com/watch?v=zsTDUdWylFU

Notice that the smoke comes out of the fuel cap, hence its in the tank, evap port to tank.

It burns....they use a wick and a nichrome wirepatent)

http://www.google.com/patents/US730...gTrwYHYDQ&ved=0CDoQ6AEwAg#v=onepage&q&f=false

 

[ivymike]

"if the intake purges the fumes you have to have a vent"
When you're purging the cannister, you don't have to route the purge air through the fuel tank.

"It burns....they use a wick and a nichrome wire"
really? Then why do they have a paragraph at the very end of the smoke pro brochure describing how to drain excessive condensed "smoke" back into a reservoir? Read the patent you linked to. They never mention burning the fluid, but they make repeated references to vaporizing it. They also mention that one of the primary methods of operation of smoke machines is to completely submerge the heating element in the "smoke fluid." That pretty much eliminates the possibility that those ones are burning anything.

If all you hope to get out of this thread is someone's blessing to go and do what you're apparently determined to go do (blow pressurized air into a fuel system and see what happens) then just make sure your kids aren't home before you do it, and have fun! If there is some other point to all of this, I'm missing it.