| Filter Media |
| Specification |
| All types of
filter media are specified in a similar manner. Each has its own physical characteristics which is given on their individual pages whilst their grading and its representation is common for all kinds of filter media. |
| The grain
specification of any filter media is based upon a sieve analysis. This is produced by placing a representative sample onto a stack of test sieves of reducing aperture size. The stack is vibrated until the sample has been divided into its various sizes. A table of results is recorded from which the grading curve may be drawn. From the graph the media specification is obtained. |
| Sieve | Retained | Retained | Retained | Passing |
| mm | grams | % | accum. % | accum. % |
| 2.50 | 3.50 | 2.80 | 2.80 | 97.20 |
| 2.00 | 31.50 | 25.40 | 28.20 | 71.80 |
| 1.60 | 47.20 | 38.10 | 66.30 | 33.70 |
| 1.40 | 23.10 | 18.60 | 84.90 | 15.10 |
| 1.18 | 14.80 | 11.90 | 96.80 | 3.20 |
| 1.00 | 3.70 | 3.00 | 99.80 | 0.20 |
| Tray | 0.20 | 0.30 | 100.00 | 0.00 |
| 124.00 | 100.00 |
The results are plotted on to a graph from which the media's
specification can be obtained. Three types of graphical representation
may be used which are discussed on the Graph page.
| Specification | Example | Comments | |
| Top Size | d95 | 2.50 mm | max 5% over size |
| Bottom Size | d5 | 1.18 mm | max 5% under size |
| Effective Size | d10 | 1.31 mm | 10% passing |
| Uniformity Coefficient | 1.43 | d60/d10 | |
| Hydraulic Size | 1.71 mm | see Hydraulic Page | |
| Minimum Size | d1 | 1.06 mm | 1% passing |
| Over Size | 2.80 % | maximum 5% | |
| Under Size | 3.20 % | maximum 5% | |
| Size Ratio | 2.12 | d95/d5 | |
| d60 | 1.87 mm | for U.C. calculation |