(Note: Do not include handles, screw-in adapters, etc. when
measuring length.)
What are the different types of filtration for a Pool or Spa?
There is a lot of confusion about various filters, and many
different opinions. Here are a few facts to consider. The first is
that a pool can be properly maintained with any of the filter
systems available: Filter Cartridge, Sand or Diatomaceous Earth
Swimming Pool Filter Systems. Here is a brief description of each
type:
Filter Cartridge (The economic low maintenance filter).
This one is easy to understand. Water passes though a filter
material and the filter captures the debris. This is just like the
water filters used under your sink. Cartridges have much more
available area to filter than sand. Most start at 50 Sq.ft and the
majority of the cartridge filters sold are larger than 100 Sq.ft.
Cartridge Filters are designed to run at lower pressure than sand.
This puts less back-pressure on the pump and hence you get more
flow and turnover for an equivalent pump size. Generally these
filters have to be cleaned once or twice a season by simply hosing
them off, so you don't touch them as often. In terms of particle
size filtered out, cartridge is somewhere between sand and DE.
Sand (The older style filter)
Water is pushed through a bed of filter sand and removed through a
set of lateral tubes at the bottom. The filter area of a sand
filter is equal to the area of the filter itself. For example, a
24" filter will have 3.14 sqft of filter area. Only the top 1" of
sand is actually used to filter the water. The principle behind
this filter is that water is pushed through the filter sand,
somewhat like an espresso machine. Dirty water goes in the top and
clean water exits out the bottom.
As the filter sand becomes plugged with debris from the pool, the
pressure increases on the filter and the water flow drops. In order
to clean the filter, you just run it in reverse and dump the waste
water; this is referred to as "back washing" the filter. Once the
filter is back washed, you move to the rinse mode and that repacks
the sand and then back to filter. This has to be done manually
every few weeks. From a hydraulics standpoint, a backwash valve is
typically the most inefficient piece of equipment you can add to a
swimming pool system. Should the sand ever become really dirty, it
is easily and inexpensively replaced. In terms of particle size
filtered out, sand is the lease effective method - it can allow
smaller particles to pass back into the pool.
DE (Low-usage alternative)
Diatomaceous earth is mined and is the fossilized exoskeletons of
tiny diatoms. They are used to coat "grids" in the filter housing
and act as tiny sieves to remove debris. They are very small and as
such can filter out particles as small as 5 microns. Diatom filter
area are sized between sand and cartridge - around 60-70 sq ft are
most common. Once the filter pressure rises, the filter is back
washed just like a sand filter and then "recharged" with more DE
powder. Typically it is poured in a slurry into the skimmer and it
then coats the filter grids. DE filters run at higher pressures
than cartridge filters and as such can lead to some inefficiency
and flow loss.
NOTE* Spa-Daddy does not recommend the use of diatomaceous earth
(DE) with cartridge filters. DE Particles will become trapped in
the body of the media and shorten cartridge life.
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