On Sat, 16 Jul 2011 11:07:33 -0700, harry wrote:

That seems very low. Â*My facts may be wrong but I think 30ft of water
creates 1 atmosphere of pressure, which is about 14 lbs/sq.in.
So the cast iron boiler on the ground floor of my house Â*is under
about 15 ft of head from the loft cold tank, which equates to around 7
lbs/sq. in.
What have I got wrong?

Guy Gorton- Hide quoted text -

- Show quoted text -

No that is correct. They had huge pistons and very long strokes.
Early steam engines actually ran on vacuum.

Except, of course, for Trevithick, and anyone else utilising his patent
(all early locomotive builders, for example..). Trevithick engines ran
on "strong steam" - 35psi plus, often didn't use condensers, derived
all power from the force (and a little bit of expansion) of the steam
and generally had small pistons (8.25" diameter in the Pen-y-Darren
machine - one of the few things we know for sure about its design).
Cylinders were still very long in early Trevithicks (4'6" in the
Pen-y-Darren machine) though some of this would have been to cope
with condensation in the cylinder (no drain cocks in those days).

--
From the Model M of Andy Breen, speaking only for himself