The pressure gauge on a steam condenser for a turbine indicates 26.2 in. Hg of vacuum. The barometer reading is 30.4 in. Hg. What is the absolute pressure (psia) in the condenser ?

according to my knowledge (not a lot),

The barometer reading is gauge pressure as most pressure measuring devices gives the gauge pressure .

According to the formula

Absolute pressure = gauge pressure + atmospheric pressure .

What is the atmospheric pressure according to this ? And why ? I'm not sure .

What does the 26.2 in. Hg of vacuum means ?


1 Answer 1


Two corrections:

  1. A barometer measures the atmospheric pressure, relative to a vacuum at zero pressure. Just look at the original barometer (and the source of the use of inches of Hg). A 40 inch long tube is filled with mercury and inverted into a beaker of mercury. The mercury falls until the pressure of the column of mercury equals the pressure of the atmosphere.

  2. A pressure in inches of vacuum is measuring the gauge pressure; the pressure between the interior of the tank and the outside atmosphere. The only quirk is that a lower interior pressure has a positive value. The pressure is that much below the reference atmospheric pressure. So a tank with a pressure of 20 in Hg vacuum also has a pressure of -20 in Hg gauge pressure...


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