Cartridge
filtration has been available for a relatively long time,
but only recently has it begun to enjoy rapid growth and acceptance.
When water passes through a cartridge filter,
dirt is screened out at the surface of the cartridge element.
When clean, the element will trap larger particles, with finer
particles being filtered out as the pores of the element become
clogged by the larger debris.
The cartridge element can be removed and cleaned by pressure washing
inside and out with a garden hose.
Sand Filters
The oldest
and most popular method of filtration is sand. Sand filters
share two things in common:
1) When in the filtration mode, water always
flows from top to bottom.
2) They all have some sort of lateral or
underdrain with slots to hold back sand while allowing clean,
filtered water to pass through.
High-rate 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 serve to separate particles, allowing filtration
to take place. They operate on the basis of "depth" filtration;
dirt is driven through the sand bed and trapped in the minute spaces
between the particles of sand. Initially, a clean sand bed will
remove larger particles, and then, as the bed starts to load up
with dirt, it will remove finer particles.
Cleaning of the media, or sand, is accomplished
through reversing the flow through the filter, to the "waste"
line. This is known as backwashing.
DE 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.
