On Fri, 16 Jan 2004 21:04:51 +0000 (GMT), "Dave Liquorice"
wrote:

I doubt they switch back though, which would
allow you to toggle between cylinders. As one became too cold to
vapourise the valve would switch to the other, allowing the cold one
to warm up. When the second got too cold the valve would switch back
to, the now warm, orginal cylinder. B-)

AFAIK they don't switch back.

One method (I've seen it both in books, and on a building site feeding
big heaters) is to run several tanks parallel. This reduces the amount
of vapor each tank has to produce, while the surface increases.

Thomas Prufer