The make-up of the pressure filter bed depends upon the size of the filter and configuration of the base,
there are eight options.
1.
2.
3.
4.
Filters under 1m diameter with laterals.
Filters under 1m diameter with nozzle plate.
Filters over 1m diameter with laterals.
Filters over 1m diameter with nozzle distribution plate.
Table 1: AFM® filter bed depths as a percentage for each grade
With flocculation, Pressure & RGF filters
Pressure filters, under 1m Ø with laterals
Pressure filters under 1m Ø with nozzle plate
Pressure filters over 1m Ø and RGF filters with
laterals.
Pressure filters over 1m Ø with nozzle plate & RGF
filters with nozzles or screened floor
Without flocculation, Pressure & RGF filters
Pressure filters, under 1m Ø with laterals
Pressure filters under 1m Ø with nozzle plate
Pressure filters over 1m Ø and RGF filters with
laterals.
Pressure filters over 1m Ø with nozzle plate & RGF
filters with nozzles or screened floor
Grade 0 optimised filters, pressure filters under 1m
Ø with laterals
Grade 0 optimised filters, pressure filters under 1m
Ø with nozzle plate
Grade 0 optimised filters, pressure filters over 1m
Ø with laterals
Grade 0 optimised filters, pressure filters over 1m
Ø with nozzle plate and RGF filters
Grade
3 Grade
2 Grade
1 Grade
0
0%
0%
15% 20%
20%
15% 80%
80%
70% 0%
0%
0%
0% 20% 80% 0%
0%
0%
15% 20%
20%
15% 60%
60%
50% 20%
20%
20%
0% 20% 60% 20%
0% 20% 10% 70%
0% 10% 10% 80%
10% 10% 10% 70%
0% 10% 10% 80%
Notes
Dryden Aqua Ltd
Butlerfield-Bonnyrigg,
Edinburgh EH19 3JQ Scotland
Page 13 of 44
Filters from different manufacturers will have different dimensions. With regards to filters that
have a lateral arrangement. In general for filters under 1m in diameter, you want grade 2 to fill
the space and cover the laterals to a depth of at least 50mm. If the filter is larger than 1m
diameter, then grade 3 should be used to fill the space below the laterals. The remainder of the
bed is then made up with grade 2, 1 & 0 in accordance to the percentages give above.