Recovering the Rest of the Material From the Spray Can

Worth a chuckle. I would just wrap a shop-rag around an awl and push it through...

You've see Bob's rattle can adapter haven't you?

=== Bob Engelhardt - 12/4/10

My version:

=== It has been posted several times. He used it to repressure paint cans with a propane bottle. Was in this discussion/thread for one:

"spray$20can"$20repressure/rec.crafts.metalworking/t_yer8lTjjo/yE0q-konj6kJ

Depress nozzle on can, apply rubber tipped blow gun and add compressed air. Done.

At least for WD40, oils and solvents. Air might might make paint harden in the can, so propane might have an advantage there.

You can do a similar thing with Butane lighter refill adapters. I like the lower pressure of Butane.

Could probably do the same thing with "canned air", but I've never tried it.

I have a dead can of hornet spray. Was all set to put some Butane in it...then got to thinking how it would feel when the can of poison exploded in my face.

Some things aren't worth the risk of fixing 'em. ;-)

How about using your argon? Everybody has argon around the shop.

The advantage of propane is that it's liquid and maintains a constant pressure that is its vapor pressure. Until the very end, of course. With air, or any gas, the pressure will decrease as it's used.

Bob

The disadvantage is that its pressure depends on how well it dissolves in the liquid in the can, and the relative quantities of product and propane which you can't easily determine or control.

's_law "If a non-volatile solute (zero vapor pressure, does not evaporate) is dissolved into a solvent to form an ideal solution, the vapor pressure of the final solution will be lower than that of the pure solvent."

If it doesn't dissolve the pressure may exceed 200 PSI.

-jsw

I had never thought about that. Yet, you're putting 2 liquids in a can, one could dissolve in the other. But it's moot if the original propellant was propane, which I assume it was. Moot because you're just doing what the factory did.

Bob

Well, yeah but ... the vapor pressure of CO2 at room temperature is about 900 psi, IIRC. Whereas for propane it's 100 psi, again IIRC.

That holds true with C02 as well, but pressure does fluctuate with temperature.

The vapor pressure of CO2 dissolved in soda water is much lower, as is that of acetylene dissolved in acetone. Unless you make a connecting hose with a pressure gauge and shutoff valve you don't know how much pressure the can should have, or how much you are adding.

When I did this in college I tested the pressure by denting the can with my thumb, which I can just barely do at the original factory pressure. I used a little fitting that jammed into the stem of one can and sealed with a taper in the stem of the other, and pressed them together with the butane on top.

I'm still entranced by the fact that I have air at 100psi!