Filtration System Types
&
Design Factors

Hourly flow rate:

The hourly flow rate depends on the amount of time specified for the circulation of the all the water in the pool.

Most domestic pools are designed for a pool water turnover period of 6 hours. Hence a 10m x 5m x 1.5m deep pool will have a required pumping rate of 10 x 5 x 1.5 /6 = 12.5 cubic metres per hour.

Commercial pools have far more stringent criteria and hence much higher pumping rates are required.

Speed of Filtration:

Sand Filters

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

The required filter area is = the hourly flow rate / 50.

This is far from ideal and Bluepools limits the flow rate to 30 metres per hour as this results in much cleaner water.

So for example, for a flow rate of 13 cubic metres per hour the required filter area is 13 / 30 = 0.43 m2.

The sand filter area is 3.14 x diameter x diameter / 4 and so the filter size required is 740 mm or a 0.75m sand filter. This would reduce to a 0.6m filter if the flow rate is increased to 50m / hour.

Speed of Filtration in Other Filter Types

Filter Type	Allowable Filtration Speed
Cartridge	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	Particle size allowed through filter
Sand	20 to 40 microns
Cartridge	10 to 25 microns
Diatomaceous Earth	3 to 5 microns

Zeolite:

Zeolite is the name of the new wonder filter material that makes pool water amazingly clear and sparkling but is very costly.

Glass Filtration Media:

Crushed, graded glass works exceptionally well and is now nearly as cheap as sand and is being used far more frequently.