FILTRATION
Provided Courtesy PacFab Incorporated
FILTERS
The purpose of a filter in a pool or spa
circulation system is to remove insoluble matter such as dirt, debris, algae,
etc. from the water. Filters work by screening out the above particles. Filters
remove dirt by SIMPLE DILUTION. This means that as the filter removes the dirt
the pump returns the clean water to the pool. The clean water dilutes the dirty
pool water. Therefore, it takes time to continually dilute the water until it
becomes "clean". A filter removes dirt (organic particles); it does not purify
water chemically. Filters will operate on either the vacuum or pressure side of
the system. The primary filter used in pools and spas is the pressure type,
which is installed after the pump. On vacuum systems the filter is installed
before the pump. Pressure filter systems are available in three types: Sand,
D.E. and Cartridge.
SAND FILTERATION
The High Rate
Sand Filter is the most common type of filter used throughout the United States
and in most other countries. It is a permanent media, depth type filter. If the
water chemistry is properly maintained the sand media is often used for a 10 to
15 year period. Most residential sand filters are rated at 20 gpm per sq. ft.
while commercial sand applications will be rated at either 15 or 20 gpm per sq.
ft. This rating is approved by the National Sanitation Foundation (NSF), but is
subject to local and state codes. Flow is a critical factor in the proper
operation of any filter, in particular on the filtration and back- wash cycles.
To "properly" backwash a sand filter a minimum of 15 gpm per sq. ft. is
required. Another important factor in sand filtration is the type of sand used;
it should be of a type specified for use with swimming pool filters. The
typical sand used is a N0.20 Standard Silica, with a Uniform Coefficient not
greater than 1.75, .018" -.022" particle size. Pea gravel is another media
commonly used in conjunction with sand. The pea gravel is placed at the bottom
of the tank, covering the laterals and then sand is placed over the pea gravel.
The use of pea gravel will enhance the backwash cycle. Pea gravel should be 1/8
to 1/4" diameter in size.
OPERATION
A sand filter
works by trapping dirt in the voids between the grains of sand. As dirt builds
up the voids become smaller thereby trapping progressively smaller particles.
The finest particles in size are removed just before backwashing. Backwashing
should be done when the pressure gauge increases 8 to 10 psi above starting
pressure, flow rate will also diminish as the filter becomes dirty. During
backwash the flow is reversed, now flowing from the tank bottom (laterals) to
the top, removing the trapped particles and taking them to waste. After
backwashing, a sand filter removes particles in the 50 to 100 micron range (1
micron = 1 millionth of a meter). Since a pool is cleaned by passing the water
over and over again through the filter (simple dilution) the filter first
removes larger particles and then perhaps down to the 25 micron range. NEVER
back- wash a sand filter on a TIME basis otherwise only small dirt particles
will be left in the pool (in the 25- 50 micron size range) and they will
continually pass through the filter bed.
Follow
manufacturer's instructions when installing, initially starting up and
operating your filter.
STEPS FOR BACKWASHING SAND
FILTERS:
CAUTION: To prevent equipment damage
and possible injury, always turn off pump before changing valve
positions.
1. Stop pump.
2. Ensure that the suction
and backwash lines are open so that water is free to come from the pool and
flow out the backwash line. Set control valve position as follows:
a. If
using multiport valve, set valve to backwash position.
b. If using two
position slide valve, push handle down to backwash position and engage lock by
twisting handle.
3. Stand clear of filter and start pump.
4.
Backwash filter for approximately (2 to 5 minutes) or until backwash water is
clean.
5. Stop pump.
a. If using multiport valve, set valve to
rinse position and continue with remaining steps.
b. If using two position
slide valve, skip to Step 8.
6. Stand clear of filter and start pump.
7. Rinse filter for approximately 30 seconds.
8. Stop pump and
set valve as follows: a. If using multiport valve, set valve in filter
position. b. If using two position slide valve, raise handle to filter position
and engage valve lock by twisting handle.
9. Ensure that pool return
line is open so that water may freely flow from the pool back to the pool.
10. Open manual air bleeder. Stand clear of filter and start pump.
11. Close manual air bleeder on the closure when all the air is removed
and a steady stream of water emerges from the bleeder.
12. The filter
has now started its filtering cycle. You should ensure that water is returning
to the pool and take note of the filter pressure.
13. The filter
pressure in Step 12 above should not exceed the pressure originally observed on
the filter when it was initially started. If after backwashing, the pressure is
4 to 6 PSI above the start condition it will be necessary to chemically clean
the sand bed.
WARNING THIS FILTER OPERATES
UNDER HIGH PRESSURE!
1. You MUST turn off the complete system and open
all air bleeders BEFORE servicing any equipment or re-positioning any valves.
2. You MUST follow all instructions in the EXACT order presented in
your Operator's Manual.
3. You MUST reassemble all clamps, closures and
fasteners properly.
4. Upon start-up, with air bleeder open, you MUST
stand clear of the filter until all air is expelled and a steady stream of
water from air bleeder is obtained.
