VAPOR PRESSURE
Knowledge of vapor pressure is extremely important when selecting pumps and their mechanical seals. Vapor pressure is the pressure absolute at which a liquid, at a given temperature, starts to boil or flash to a gas.
Absolute pressure (psia) = Gauge pressure (psig) + Atmospheric pressure.
Let’s compare boiling water at sea level in Rhode Island to boiling water at an elevation of 14,110 feet on top of Pikes Peak in Colorado. Water boils at a lower temperature at altitude because the atmospheric pressure is lower.
Water and water containing dissolved air will boil at different temperatures. This is because one is a liquid and the other is a solution.A solution is a liquid with dissolved air or other gases. Solutions have a higher vapor pressure than their parent liquid and boil at a lower temperature. While vapor pressure curves are readily available for liquids, they are not for solutions. Obtaining the correct vapor pressure for a solution often requires actual laboratory testing.
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