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Home-pool filters
Sizing and Selection
Techniques on Swimming Pool filters
There are
certain health and safety codes in place that state that filter
systems must have certain turnover rates and filtering abilities for
gallons per square foot of filter area. Some of the following
guidelines will assist you in calculating this criteria.
First you need to calculate the volume so that you may determine how
much water must be filtered. Following are a few easy formulas and
procedures to help you calculate the volume of your swimming pool:
For a circular pool, multiply the radius by the radius by 3.14 (pi)
by the average depth; for a rectangular pool, you need to multiply
the length by the width by the average depth. Oval pools are not
accurate ovals; they are actually rectangles with semicircles.
Therefore, you need to either combine the formulas for circular and
rectangular pool or use the grid technique. For the grid technique,
make a scale drawing of the pool on square grid graph paper; each
square would represent one square foot or any standard unit of
measure. Then add up the number of squares, including those that are
partially filled. This will give you an approximate estimate of the
pool's
area in square feet. Then multiply the area by the estimated average
depth of the pool. This will provide you with the volume in cubic
feet.
In order to calculate the pool's capacity or the number of gallons
of water that will fill the pool, multiply the pool volume by 7.48
(which is the number of gallons of water in a cubic foot of volume).
If you have a rectangular pool that is 40 feet long and 20 feet
wide, with an average
depth of 5 feet, multiply 40 x 20 x 5 which equals 4,000 cubic feet.
then put the volume into the capacity equation and multiply 4,000 x
7.48 which equals 29,920 gallons.
The flow rate is the volume of water flowing past a particular point
during a certain period of time, measured in gallons per hour (gph)
or gallons per minute (gpm). In order to compute the flow rate,
divide the volume of the pool by the turnover rate, which is the
amount of time needed for the body of water to flow around the
capacity of the pool. For example, if you set up the pool to have an
8-hour turnover rate, in order to achieve that rate, it will depend
on which filter you install. For this reason you must first decide
on the desired flow rate (one that will assist the turnover of which
you are searching).
It does not matter the shape of your pool for the equation to
determine the flow rate for the 29,920 gallon pool. So 29,920 ¸ 8 =
3,740 gph. To obtain the flow rate per minute, divide the flow rate
per hour by 60. Thus, 3,740 @ 60 = 62.3 which would be the rate at
which the filter should operate.
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