MadSci Network: Engineering

Re: What is the relation between pounds of steam to gallons of water/min ?

Date: Fri Sep 29 12:12:11 2000
Posted By: Allan Harvey, Staff,National Institute of Standards and Technology
Area of science: Engineering
ID: 970148517.Eg

Your question does not quite make sense as worded.  So I'm going to try 
and answer what I think you might have meant.  If this does not answer 
your question, then you can resubmit with more explanation of what you are 
talking about.

A pound of steam is a certain mass; if you condense the steam you would 
get a certain number of gallons of water (still the same number of pounds, 
of course).  The relationship between the two would be given by the number 
of pounds in a gallon of water.  This varies with temperature, it is about 
8.3 pounds per gallon at room temperature.

But often the term "pounds of steam" has a different meaning, referring to 
the pressure (not really in "pounds"; this is short for "pounds per square 
inch") at which the steam was generated.  As you probably know, water 
boils at a higher temperature at higher pressure (about 100 degrees C at 
one atmosphere pressure, a pressure cooker gets hotter, water boils at a 
lower temperature at high altitude).  So if somebody says "200 pound 
steam" (or "200 psi steam") they mean steam generated by boiling water at 
that pressure (from the Steam Tables, I find that such steam would be at 
about 382 or 387 degrees Fahrenheit, depending on whether the "200 psi" 
was absolute pressure or gauge (amount above 1 atm) pressure).  The higher 
the pressure of generation, the higher the temperature and the more can be 
done with the steam industrially.  So a chemical plant might have steam 
lines running around at different pressures (perhaps labeled 500 psi 
steam, 200 psi steam, 100 psi steam, etc.) with the higher pressures being 
used when they need something hotter.   
I can't think of any connection between this concept of "pounds of steam" 
and "gallons of water per minute".

Finally, I will mention that you can find some general information on 
properties of water and steam under the "FAQs about Water and Steam" 
section of:

Allan Harvey
"Don't blame the government for what I say, or vice-versa."

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