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The Hydraulic Size of a filter media is the size it would have if all the grains were of one uniform size. The material would then have the same hydraulic loss as the sample. The hydraulic size is the averaged area used in the Carman/Kozeny equation in the determination of the hydraulic gradient through a filter bed.

The example below uses the results from the specification page

Calculation of the Hydraulic Size
Sieve mm Retained % Retained/Sieve
2.50 3.10 1.24
2.00 20.40 10.20
1.70 29.60 17.41
1.40 30.10 21.50
1.18 13.80 11.69
1.00 [tray] 3.00 3.00
Totals 100.00 65.04
1 Divide the percentage retained by the sieve size
2 Total the calculated numbers 65.04
3 Divide the result by 100 0.65
4 Take the reciprocal 1.54
5 Add 10% 1.69
Result The Hydraulic Size of the sample is 1.69mm