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Sand
filters
The sand in a sand filter (#20 silica
sand; 45 - 55 mm) is specially graded to
trap particles in the 20 - 100 micron
range. As a sand filter collects dirt,
its efficiency increases, trapping more
dirt. When your pressure gauge shows a
reading 8 - 10 lbs. over its clean,
start-up reading, it is time to backwash
the captured dirt out of the filter.
"They Say" that a sand bed should be
replaced after seven years. Gradual loss
of efficiency may be hard to notice. If
your filter requires frequent
backwashing, every week or two, the sand
bed may be "mudballed", or it may be "channeled". It may also "calcify"
with calcium deposits. Other water balance problems may also contribute to sand
deterioration, but a properly sized filter could go over 10 years between sand changes.
Use of
Biguanide chemicals, i.e., Soft Swim or
Baquacil require annual cleaning of the sand to prevent it from "gumming up".
High amounts of bather oils can gum up a sand bed. And just the years of a pump forcing
water over the grains wears away the sharp edges of the sand. Such sand becomes more
circular, and traps dirt less efficiently.
Remember that for sparkling water, we need the trio
of sanitation, filtration and circulation. If one of these areas is lacking, the
water won't look so hot. So, if you've kept very good chemical maintenance and your
circulation is good, you may have a filter problem. Is the filter sized properly? Many
filters of the 70's - 80's were grossly undersized, the trend now in pool filtration is
"Go Big Early".
Adding a
small amount of aluminum sulfate or "alum", through the skimmer will form a
gelatinous layer on top of the sand bed, useful in cleaning up an undesirable water
condition. You can also add a small amount of DE powder or
other filter media.
"How do I Backwash my Sand Filter"
When the pressure gauge is reading 8 - 10
lbs above the clean, starting pressure
(after backwashing), it is time to
backwash the filter. This process
involves turning a valve so that the
water will flow through the filter
backwards, flushing out the dirt. Hence
the name "back-washing." Sand filters can
have either a push-pull valve (aka slide valve) or a multiport valve. The multiport valve has multiple ports on the valve, usually 6 positions:
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FILTER: Keep it here 99% of the time, except when backwashing, rinsing or wasting
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RINSE:
Use this
setting for 20 seconds after backwashing to rinse tank
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RECIRCULATE: Use this
if the filter's broken; at least you're circulating.
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BACKWASH: Use this
setting to reverse the flow in the filter and send water out of the waste
line. Make sure valves are open or hoses rolled out.
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CLOSED: Put here to
close off flow from the pool, usually to work on the equipment. Do not operate pump with
valve in closed position
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WASTE/DRAIN: Another
filter bypass setting, but this one sends the water out of the waste pipe (hose), instead
of returning it to the pool. Used to lower pool water level or to vacuum to waste.
So, to backwash a sand filter with a
multiport valve;
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Shut
off the pump motor.
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Press
down on valve handle, rotate valve from
FILTER to BACKWASH position.
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Roll
out any backwash hose or open any waste
line valves.
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Open air bleeder assembly on filter, and
turn pump on.
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Watch
pressure gauge for backpressure and hose
for kinks. Be prepared to shut off pump
quickly.
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After
hose fills with water, run for 2 - 3
minutes or until water runs clear.
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Shut
off pump motor and move multiport valve
handle from BACKWASH to RINSE position.
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Run on rinse
for 15 - 25 seconds.
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Shut
off pump motor and move multiport valve
handle from RINSE to FILTER position.
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Turn
pump back on and note lower pressure.
Roll up backwash hose.
To Backwash a sand filter with a slide
valve;
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Shut off pump motor, roll out backwash
hose (if you have it).
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Twist to unlock plunger T-handle, pull/
twist plunger upwards 2 - 3".
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Open air bleeder assembly on filter, and
turn pump on.
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Watch pressure gauge for
backpressure (+ 40 psi) and hose for
kinks. Be prepared to shut off pump
quickly.
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After hose fills with water, run for
2 - 3 minutes or until water runs
clear.
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Shut off pump motor and push T-handle
back down into locked position.
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Turn pump back on and note lower
pressure. Roll up backwash hose.
A properly sized sand filter should, in most cases,
be able to operate continuously for a period of 4 weeks between backwashings. A
"Filter Run" of less than 4 weeks may indicate sand problems (or sizing
problems).
Sand in the pool?
Bad news. If it hasn't blown in, or been carried in on the feet of swimmers, it's
likely coming from the filter. A broken
lateral or
standpipe may be the cause. You'll need
to empty the tank, locate and make the repair, refill with fresh sand and test.
Sand bed replacement
To replace filter sand, you'll first
need to empty out the existing sand. One
method is to spread a tarp out beneath
the filter drain assembly. Then remove
the entire assembly, turn on the pump,
and step back! The water pumping through
the filter will remove most of the sand
out of the drain hole. Another method is to
remove the drain plug only and allow the
filter to drain for several hours or
days. Then, remove the top dome or multiport valve.
If you have the Triton style dome on the
top of the filter, you'll need the
octagonal dome wrench to remove the
dome. Once the dome is removed, gently
twist the baffle/pipe out......
(continued........)
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