MadSci Network: Engineering

Re: How is vacuum affected by atmospheric pressure in a steam condenser

Date: Tue May 23 09:16:07 2000
Posted By: Richard Bersin, Other (pls. specify below), Senior Technical Staff Member, Emergent Technologies
Area of science: Engineering
ID: 957796674.Eg

Dear Mark:
I can think of only one reason for your observations based on your 
description of the turbine operation.  The gauge which reads the pressure 
(or vacuum) in the condensor must not be an absolute gauge, but one which 
reads the pressure difference between the atmosphere outside and the 
pressure inside the condensor.

So when the atmospheric pressure goes down the gauge inside reading the 
vacuum reads less because the difference in pressure between the vacuum and 
the atmosphere has decreased.  To avoid this confusion you would have to 
make a corrction for the change in atmospheric pressure.  Since the 
atmospheric pressure gauge reads the true absolute pressure, you should 
subtract 1000 from the atmospheric pressure reading; and then subtract that 
number from the reading of the condensor gauge to get the true pressure in 
the condensor.

I hope this clarifies things for you.

R. Bersin.

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