Skeleton Man wrote:

> Hi all,
>
> I've always wondered why those air duster cans use R134 or simmilar
> refrigerants, etc instead of some other chemical or simply air ? (or even
> CO2)
>
> What also puzzles me is why it's illegal to vent R134 into the atmosphere
> from your air conditioner, but you can buy sprays cans full of it at any
> electronics store ?
>
> Anyone have any theories here ?
>
> Chris

Air duster cans containing just plain air are available ... but don't buy
them: they quickly run out of pressure because the contents is just
compressed gas. Some gasses (like R134 and "Freon") liquify at reasonably
low pressure, so a can of R134 is mostly liquid that gradually returns
to gaseous state as it is allowed to escape. Result: a can of R134 gives
much more gas than a same-size can of air (which doesn't liquify at can
pressure), and the nozzle pressure remains constant until the last bit of
liquid in the can boils off.

CO2 liquifies at about 800psi. It would do the job if supplied in a
vessel capable of withstanding that pressure. The small CO2 cartridges
used to pressurize seltzer bottles or air guns might serve ... but
would be awkward to use with an 800psi gas stream. A regulator would
solve that problem, but at unacceptable cost.

Propane liquifies at reasonable pressure and is used as a propellant
in aerosol cans ... but you wouldn't want to use it anywhere there is the
possibility of ignition.

Bryce