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An Overview of Air Permeability Testing

What is Air permeability ?

Air permeability is an important factor in the performance of such textile materials as gas filter, fabrics for air bags, clothing, mosquito netting, parachutes, sails, tent age, and vaccum cleaners.  It can also be used to provide an indication of the breathability of weather-resistant and rainproof fabrics.



Construction factors and finishing techniques can have an effect upon air permeability by causing a change in the length of airflow paths through a fabric.Fabrics with different surface textures on either side can have a different air permeability depending upon the direction of air flow.


Air permeability tester Test Procedure:

1、Suction pump ‘A’ draws air through the test specimen ‘S’ at 20±2oC and 65±2% R.H. The rate of flow is controlled by the by – pass valve ‘B’ and the series valve ‘C’.
2、The rate of flow is adjusted until the required pressure drop across the fabric is indicated on a draught gauge ‘D’ which is graduated from 0 to 25 head of water.
3、‘E’ is a reservoir which smoothens out any disturbance due to varying velocities of the streams of air drawn through the various paths by the pump.
4、When the required pressure drop, which is normally 1 cm of water, is attained and the indicator of the draught gauge is steady, the rate of air flow is read off one the four Rota meters ‘R’, selected according to the permeability of the test specimen.
5、The Rota meters are calibrated, at 20oC and 760 mm of mercury to indicate air flow in cm3/sec and they cover the following ranges :
R1: 0.05-0.5
R2: 0.5-3.5
R3:   3-35
R4: 30 – 350
6、Gradually  open  ““Valve  C””  (on  the  right  side)  until  the  required  pressure  is  shown  on  the  manometer
tube.
7、The test is commenced with R4 open and the other Rota meters closed. If the flow is less than 30 cm3/sec, R3 is opened and R4 closed.
8、This procedure is repeated until the most suitable range for the fabric under test has been selected.
9、To prevent damage to the draught gauge a safety valve F is provided.
10、The test area is 5.07 cm2 and from the readings on the Rota meter either the air permeability or the resistance can be calculated.
11、The average rate of flow from five specimens is calculated .
The results can be obtained by using the following formula –

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