Clean, Dry Air: Pressure Media for Calibration Equipment Manufacturing

Calibration equipment manufacturers implement significant measures to ensure the media used during production is clean, dry and free of particulate and liquid contaminants. Calibration equipment users should take their own measures to ensure the media used in the instruments is also free of contaminants.

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For example, all Mensor pneumatic controller data sheets specify the acceptable pressure medium as “Dry, clean air or nitrogen (ISO 8573-1:2010 class 5.5.4 or better).” Air that is used in any Mensor pneumatic instrument should meet or exceed the requirements of ISO 8573-1:2010 class 5.5.4, which specifies purity classes of compressed air with respect to particulates, water and oil.

The class 5.5.4 specifies the following levels for clean, dry air. The suffix "5.5.4" relates to the following levels of purity:

  • "5" - Solid particulate in the size range from 1-5 microns must be less than or equal to 100,000 particles per cubic meter.
  • "5" - The water vapor dew point must be less than or equal to 7 °C.
  • "4" - The total oil (vapor/liquid) must be less than 5 milligrams per cubic meter.

The following is an explanation of how the Mensor facility achieves this to ensure optimal performance and cleanliness inside the products delivered for sensitive applications in critical industries.

The Mensor compressor supplies air at approximately 145 psi. It has a built-in aftercooler that removes some of the moisture.

The air is then fed through a particulate filter that removes particulates down to 1 micron/0.1 ppm oil. Next, the air goes through a coalescing filter with a rating of 0.01 micron/0.01 ppm oil removal. From there, the air goes through a refrigerated dryer that lowers the dew point to 37 °F.

At this point, the air is divided between the 140 psi supply for production to meet manufacturing requirements, and the supply for the nitrogen generator.

Before entering the nitrogen generator, the air is fed through a carbon tower to lower any oil vapor content (VOC C6-C16, as defined by ISO 16000-6) to 0.003 mg/m3 or less. Between the carbon tower and the nitrogen generator, the air goes through another particulate filter with a rating of 1 micron. After exiting the nitrogen generator, the purity level is 98.9-99.0% nitrogen. This nitrogen is then sent through an additional particulate filter with a rating of 1 micron before being sent to the high pressure compressor.

The high pressure compressor raises the nitrogen pressure to ~3000 psi. As the nitrogen leaves the high pressure compressor, it goes through an oil/water separator. Finally, the nitrogen goes through an activated charcoal filter that reduces the oil droplet and vapor level to less than 5 mg/m3 before it is sent to the production area.

All these procedures are in place to ensure the pressure media used while building and testing a Mensor instrument does not cause any ill effects or contamination. That being said, in order to ensure the medium used in a Mensor instrument after shipment does not cause damage, precautions to reduce contamination in your supply of both air and nitrogen should be taken.Find out how safety, cost and application factor in to which gas media should  be used for pneumatic pressure calibrations.

Typically, most users choose nitrogen with Mensor products and this can be purchased in one of three ways:

  • Nitrogen dewars
  • Nitrogen cylinders
  • Nitrogen gas generators

Your nitrogen supplier or equipment manufacturer will specify the levels of purity for the nitrogen delivered, and will typically have very low particulate, moisture and oil levels compared to the requirements for compressed air. The supplied nitrogen should be safe as a medium in any calibration or measurement instrument. However, delivery to the point of use can also introduce contaminants. Filtration to reduce particulate contamination (1 micron recommended) and precautions to eliminate the introduction of any oil or water should be considered.

Clean, dry air and nitrogen are both suitable for use in Mensor instruments, but contamination levels should be within the limits given by the ISO standard. Typically, air is used for lower pressures and nitrogen for higher pressures. The equipment and procedures used to deliver air and nitrogen to every aspect of the manufacturing process is in place to deliver contaminate-free products. Using the same quality of pressure media will ensure long and productive utilization of your pressure calibration and measurement equipment.

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