Measuring the volume of air
that passes through the filter
Inflate a large plastic bag by holding it over the exhaust port of the vacuum cleaner.
Measure the circumference along the three dimensions by placing a string or tape measure loosely around the bag, as illustrated here.
Determine the volume by using the average circumference (C) and the following formula:
V = C3 Ž 6¼2 1 ft3 = 0.028 m3
Place the inflated bag over the intake port of the air sampler and vacuum cleaner, and note the length of time (in minutes) it takes to suck all the air out of the bag. Be sure that there is a tissue over the sampler cup, so that the correct conditions are reproduced. This will produce the flow rate (vol/time) following the formula:
Flow rate = volume (ft3) x 0.028 m3/ft3 x 1/n minutes x 1 min/60 s = cubic meters per second
Calculate to two significant figures only.
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