> > The very first steam engines had a piston that was several FEET in
 >  
 > > And they worked at '0' PSI steam pressure.
 >  
 > "0" can be measured. If you have "0" PSIG, then you don't have 
 > steam. Now pressure measured in inches of water column, (in.W.C.) is 
Wayne,
 You missed the first part of my story. Those early steam engines did, in 
fact, work at '0' steam pressure. The purpose of the steam was to displace 
the air. Water was then sprayed into the cylinder to condense the steam, 
causing a vacuum, so that the atmospheric pressure on the other side would 
cause the piston to stroke.
Yes, it might have had a measurable pressure in inches of water column, but 
the effective pressure was essentially '0'.
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