John & Susan Merrell
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Scio, OR 97374
503-551-7219 (cell)
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Air Flow

The Air Flow method of fiber analysis was, and for certain fibres still is, the mainstay of routine diameter measurement of fiber. It is relatively is quick, simple, inexpensive and accurate on most types of wool. It is perhaps the first braodly used laboratory based testing regiment for wool.

The basic principle of the Airflow method the applicationof a constant air pressure to a fixed mass of wool in a standard volume chamber and to measure the resulting flow of air through the sample. The surface area of the fibrers creates a resistance to the flow of air, and this flow can be accurately measured on an Airflow meter.

Finer wool causes greater resistance to the flow of air than coarse wool. Using international accepted IH (Inter-laboratory Harmonization) wool tops of known diameter it is possible to calibrate the Airflow meter to produce surprisingly accurate results, with a couple of exceptions:

  • Medullated Wools, due to the fact that their hollow inner core decreases their density in relation to that of non-medullated fibres. A finer result is produced using the airflow method than if the fibres were measured using the LASERSCAN or Projection Microscope.
  • Lambs wool, because it may differ in density to adult wool and often contains some degree of medullation and it tends to have a fine pointed tip.

If properly administered, Air Flow testing is certified by the IWTO. The Air Flow method is, however, limited in the data it provides and far too cumbersome to be of use to the individual breeder. 

Proper calibration of the testing instruments require specially obtained tops  available from a single certified supplier, and the testing regimen requires tightly controlled environmental variables, to include temperature and humidity. 

It is primarily of use wool buyers interested in the quality of scoured bales.

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