filters backwashed with water only

Most of the time, these filters are loaded with a single filtering layer of sand or of anthracite. The maximum head loss reached at the end of a cycle can vary from 0.2 to 2 bar, mainly depending on the thickness of the filter layer and on filtration rate.

Backashing relies exclusively on return water whose velocity has to be adjusted to the material’s granulometry and to the water’s viscosity and, therefore, its temperature. In general, velocity is between 15 and 50 m/h or even more at high temperature.

The velocity of wash water alone has the objective of classifying the media. This velocity corresponds to an expansion of between 15 and 30% depending on the type and the granulometry of the media.

Washing velocity is controlled by measuring the flow, the temperature, the % of expansion (level of the media during washing – level of the media at a resting state)* 100/Total height of the media at resting state). Measures are carried out in relation to floor level which is level 0.

possible configurations :

The Hydrazur filter constructed of coated steel, for high filtration rates; this system is available in a twin column version (figure 6) :

• layer depth = 0.6 m;
• 1.4 to 3 m diameters;
• main utilisation: swimming pool water.

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