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Home-pool filters
Filling in the sand
bed
Once the sand filter is charged, you will hardly ever (if ever) have
to
replace it because the sand is actually a permanent medium in
itself.
However, you must do your part to conduct routine backwashing
procedures in
order to preserve and maintain your sand filter. Another factor in
preserving your sand filter, is to charge it correctly when you
first use
it.
Find out the proper size sand to use in your filter. Filter sand is
usually
.45-.55 millimeters in diameter, which is considered pool grade #20
silica
sand. There are filters which use gravel instead of sand in the
filter bed.
The gravel requirements should be described in the manufacturer's
brochure.
The sand must not get into the circulation system. In order to keep
it out,
cover all vertically exposed plumbing or standpipes with protective
caps.
With some systems the lateral assembly in the tank will need to be
positioned before the sand is added. This is to make sure that the
plumbing
inside the system is situated correctly when the valve on top of the
filter
is put back together.
You may put some water at the bottom of the tank before putting sand
in the
tank. The water will cushion the sand when it is poured into the
tank which
will avoid damage to the lateral compound.
The different types of sand filters will require different amounts
of sand,
but a general rule is to leave 10 to 12 inches of "freeboard."
Freeboard is
the space from the top of the sand bed to the bottom of the diffuser
compound. By having sufficient freeboard, it will prevent sand loss
while
backwashing. The filter will load up with dirt quickly if the sand
bed is
too low, which will necessitate backwashing often. The sand should
be poured
carefully through the top of the filter tank. Some manufacturers
suggest
that you press the vertical standpipe as you add the sand to prevent
it from
being dislodged.
Take off the caps at the top of the filter tank and replace them
with the
top valve or dome. There are variations of this feature; some units
are
threaded into the top of the tank and some contain a clamp that
holds them
in position. All units contain O-rings to form an effective seal.
Most
manufacturers will recommend utilizing lubricant to guarantee an
effective
seal.
Correct pump and filter sizing is indicated by the flat surface of
the sand
bed. This provides the best filter efficiency without channeling.
The
following functions take place inside a typical sand filter:
The sand bed rises in the tank due to the correct flow rate through
the
filter, as the backwash process starts. In just a couple of seconds
the sand
bed will become semi-fluid, as the dirt and other solids are being
discharged to waste as they break free form the media. It only takes
about
five to 10 seconds for the sand bed to become fluid. Between the top
of the
sand and bottom of the diffuser, there is six to seven inches of
"freeboard" (the space from the top of the sand bed to the bottom of the
diffuser
compound). The sand won't rise too high provided that the pump and
filter
are sized correctly. The sand bed will begin to settle in the rinse
cycle.
After that, the filter will return to its normal form. It is
imperative that
you shut down the pump before changing the filter's valves from one
position
to another. The valve and filter itself could be damaged if you
forget to
turn off the flow.
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