How Dewpoint is Affected by Pressure

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How Dewpoint is Affected by Pressure
Dewpoint is a measurement of water vapor concentration. Water vapor, or more simply “moisture”, can be a major contaminant in process gases ranging from compressed air, to purified cylinder gases, to hydrocarbon gases, to natural gas, and many others. Moisture content can affect the gases’ quality and the detrimental effects of poor-quality process gases can manifest in various ways including:

  • Corrosion of equipment and piping systems
  • Damage to manufacturing equipment
  • Micro-organism growth
  • Effect on manufactured product quality

It is extremely important to realize that dewpoint is a function of pressure. In other words, depending on the pressure of the system being measured, the sample gas can have an infinite number of dewpoints, all dependent on the pressure of the system. The reason for this dependency on pressure is that dewpoint is an absolute indication (i.e. measurement) of water vapor pressure. Water vapor pressure is one of potentially many partial pressures that makeup a gas mixture. Each component of a gas mixture exerts its own partial pressure. The sum of all the component partial pressures equals the total pressure of the system. This last statement is essentially Dalton’s Law of partial pressures. Therefore, if the pressure of a system is altered, the partial pressure of all the components in the gas mixture will all change by the same ratio.....more.....


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Edgetech Instruments
Edgetech Instruments, Inc. is a global leader in the design and manufacture of chilled mirror dew/frost point hygrometers and other moisture and oxygen measurement devices. The company manufactures absolute and relative humidity hygrometers as well as oxygen concentration analyzers. In 2015 Edgetech Instruments achieved ISO 9001 registration certification and in 2016 the company became ISO/IEC 17025 accredited. Edgetech hygrometers are made and supported in the USA. All calibrations and certifications are traceable to NIST.

Edgetech Instrument’s products include trace moisture analyzers and instrumentation, wireless and hand held portable hygrometers, absolute and relative humidity transmitters, aircraft hygrometers, humidity and temperature test chambers and instrumentation for engine test cells. Equipment can be purchased or rented.