Hi-Rate Filters holding capacity the same as conventional

Hi-Rate Filters for Swimming Pools

The Hi-Rate Filter is a comparatively new type of filter principle, which has now been applied to swimming pools in Australia.

In appearance the Hi-Rate Filter resembles the conventional pressure sand filter. However, it operates on a completely different set of principles in its retention of solids. Flocculation of alum is not used on these filters. The incoming water is directed towards the surface of the sand so as not to cause turbulence, or disturbance of the media, passes down through the sand at high flow rates. The solids, which are in the pool water, do not remain at the surface of the media of the Hi-Rate Filter, as in the case in the conventional sand filters. They are washed down progressive into the media.

The choice and grading of the media is of the greatest importance. The sand grains have to be exactly the same size; in other words, the uniformity co-efficient must be less than 1.6. When observing the high rate filter it is seen that the solids move down into the media at a steady rate. The rate at which they travel is dependent on the quantity of the solids in the water rather than the rate of flow or the length of the filter cycle. Each volume of sand can retain a given quantity of collected solids and this is the true limit of the capacity of the filter. Comparatively, the flow rate on the Hi-Rate Filters is at least five times larger than for the conventional filter. Even though the Hi-Rate Filter only has 1/5 th the area, its dirt holding capacity is as great as the sand filter as it uses considerable depth of media compared to the shallow surface layer of conventional type. Having forced the solids deeply into the media, the backwashing efficiency must be excellent in order to discharge the collected solids. This depends on a perfectly designed and balanced internal hydraulic system. These units operate at rates of up to 16 gallons/sq.ft./min. and backwash at the same rate. An air release device is necessary on top of these filters.