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SAND
FILTERS
Sand Filter
w/side mount Backwash Valve
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This is by far the most common type
of filter we encounter in the apartment industry. These filters use sand
as a filter media. The round tank is approximately 2/3 full of a specific
size of sand that has been washed and screened. When filtering, water
enters the top of the filter and is forced through the sand bed into a
collection of lateral tubes in the bottom of the filter and back to the
pool or spa. The laterals have holes in them that are small enough to let
the water through but not the sand. As the dirt builds up in the top of
the sand bed the pressure increases. As the pressure increases the water
flow through the filter decreases.
When the pressure has increased 6 to 8 lbs. above what it runs when the
sand is clean, it is time to backwash the filter. The backwash valve
changes the direction of the water through the filter, sending it to the
laterals first and forcing it up from the bottom of the sand to the top
and then through a backwash waste line down the sewer. Most of the dirt
that has collected in the top of the sand layer is washed away down the
waste line. This usually takes a couple of minutes. An inline sight glass
on the waste line can let you see when the backwashing is complete.
Because the water is going from the inside out when backwashing NEVER
backwash and vacuum at the same time.
After backwashing, the filter pressure should return to “normal” and your
flow should increase. If your pressure is too high (normal is 10-12 lbs.)
it may be time to change out the sand. Sand collects a multitude of oily
debris that doesn’t want to backwash out and over time the sand compacts
down. Sand should be changed every 2 –3 years in a pool and every year in
a spa. It is important to remove all of the sand from a filter when
changing it. If you don’t want to do this yourself, we can give you a bid
– just call us! Going too long between sand changes will cost you more
money in chlorine and other chemicals.
A sand filter will catch particles of dirt down to about 20 microns in
size. Although quite small, an abundance of smaller particles in the water
can make it appear cloudy. Water polishes and clarifiers cause these very
small particles to bond together into big enough groups that the sand
traps them.
It is very important with all filters that the pump and filter compliment
each other. Too big of a filter on too small of a pump will not allow the
filter to backwash properly. Too much pump on too small of a filter
actually forces very small particles right through the sand. The pressure
is always too high and the internals and tank will wear out too quickly.
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Sand Filter
w/top mount Backwash Valve
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Although
these sand filters are quite a bit cheaper than side mounted backwash
valve filters we don’t recommend them for use in commercial installations.
Changing sand is more difficult and if these filters are not installed
with unions on the pipes, you must cut your pipes to get into the sand. We
don’t work on top mount valve sand filter! |
