In Ground Pool Filters
Many pool professionals consider D.E. filtration to be the finest, because it is capable of removing smaller particles than either sand or cartridge.
Diatomaceous earth is a porous powder with microscopic openings, that, when magnified, look like tiny sponges. Clear water can pass through these openings, but particles, as small as one to three microns, are trapped during the first pass through the media.
All D.E. filters have internal elements that become coated with D.E. It is this 'filter cake' that strains dirt, dust, algae and some forms of bacteria from the water.
Similiar to sand filters, when a D.E. filter becomes dirty, it is cleaned either by backwashing, or regenerating and draining, the clogged D.E. to the 'waste' line. To restore filtration, a fresh 'charge' of D.E. is added to the filter.
Pro-Series sand filters use a special filter sand, normally .45 to .55 mm (also known as pool grade #20 silica sand), because it has sharp edges that separate particles, allowing filtration to take place. They operate on the basis of "depth" filtration where dirt is driven through the sand bed and trapped in the spaces between the sand particles. Initially, a clean sand bed removes larger particles, and then, as the bed starts to load up with debris, the filter removes finer particles. The sand can be cleaned by backwashing which involves reversing water flow through the filter to the "waste" line. Sand Filters trap debris as small as 20 to 40 microns.
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