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A small mystery(7 posts)

A small mysteryBQ
Aug 4, 2001 2:06 PM
When I pump up my tires and then release the pump lever at the valve, some air comes out, and I see what looks like smoke come out, too. Happens just about every time I put air in the tires. What am I seeing? Water vapor? Something else?

There's probably going to be a simple answer and I'm gonna feel pretty stupid...
re: A small mysterybadabill
Aug 4, 2001 2:38 PM
The inside of tubes are coated with a talcum like powder, you are probably seeing this powder blow out with the air.
re: A small mysterymackgoo
Aug 4, 2001 3:23 PM
When you rapidly expand gas you lower the temp. of the gas. That's how you make LN or LOX or any gas to a liquid form for that matter. I doubt what your seeing is comming from the tube as tube pressure should be keeping the valve shut. Maybe the residual air in the pump hose rapidly expanding through the chuck and the water vapor condensing.
Just my scientific 2 cents.
yup, it's water vaporclub
Aug 4, 2001 6:09 PM
like mr. wizard said above, the air pressure in the hose is suddenly reduced, which lowers the temperature, which raises the relative humidity, which produces visible water vapor, aka, a cloud. Should only happen with a fairly high dewpoint, you live in Houston or sumthin? I used to see the same thing in PA when I pumped my track bike tires up at Ttown, the night lights made it more visible. But I've never seen it here in dry SW Colo, where the relative humidity is usually around 10 percent.
Re: yup, it's water vaporBQ
Aug 5, 2001 2:46 PM
Columbus, OH. This time 'o year, summer goes to the 90/90's... 90 degrees and 90% humidity.
Adiabatic Expansiongrzy mnky
Aug 4, 2001 9:28 PM
Allowing the volume to expand rapidly and without adding heat results in rapid cooling and can condense the water vapor contained in air to visible moisture. It's much the same principle that makes your fridge work - only you can't see it with the door closed and the light out.
The ghost of Fausto Coppi (NM)MeDotOrg
Aug 5, 2001 9:13 AM