On 16/07/2011 12:34, Clive wrote:
Very low pressures are entirely feasible considering that the steam was
only used to raise a piston which through a beam allowed what it was
working on (Man engine etc.) To drop, the steam was the condensed by
spraying in cold water and the atmospheric pressure on the other side of
the piston did the work.

Lower than you think. The beam was usually raised just by the weight of
the pump on the other end; the purpose of the steam was just to push
the air out. Then the condensation led to a partial vacuum, and the air
pressure does all the real work.

You guys really must go to Crofton Beam Engines. When they are in
steam, of course!

http://www.croftonbeamengines.org

Andy