Water Filtration Technical Data

Design Factors

Hourly flow rate

The normal rule of thumb is to calculate one eigth of the volume of the pool that is deeper than 1.5 m and to calculate one sixth of the volume of the pool that is shallower than 1.5 m. Add these two numbers together an increase the answer by 30% to allow for the flow back pressure / constriction provided by the filter.

For example in a 10 x 5 x 1 m deep pool with a 6 m long 1.8 metre average depth hopper the hourly flow rate should be:s

[( 6 x 5 x 1.8 )/ 8 + ( 4 x 5 x 1)/6]1.3 = 13 cubic metres per hour

Speed of Filtration

Sand Filters

In the sand filters the maximum filtration speed is normally assumed to be 50 m/h or 50 m³ per hour for every square metre of filter surface area. Sand filters are normally circular and of 0.5, 0 .6, 0 .75 or 0 .9 m in diameter

So the required filter area is = the hourly flow rate / 50

So with a flow rate of 13 cubic metres per hour the required filter area is 13 / 50 = 0.26 m2.

The sand filter area is 3.14 x dia x dia / 4 and so the filter size required is 570 mm or a 0.6 m sand filter.

Speed of Filtration in Other Filter Types

Filter Type
Allowable Filtration Speed


2 m3 per m2 cartridge area
Diatomaceous Earth 5 m3 per m2 filter area
Anthracite 30 m3 per m2 filter area

Particle Size Capability of Filtration Types

Filter type
Particle size allowed through filter
Sand 20 to 40 microns
Cartridge 10 to 25 microns
Diatomaceous Earth 3 to 5 microns


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