The Basics of
Swimming Pool Filters
Swimming pools and spa are subject to constant
contamination from foreign matter brought in by swimmers, wind and
articles used in and around the pool. Filtration is the mechanical
process of removing this insoluble matter from swimming pool and spa
water. Water clarity is important for appearance, hygiene and
safety. Filters are universal in pool systems, linked to the
circulation system along with the motors and pumps.
As water pumps through the circulation system
of a pool or spa, impurities are strained by a filter. The filter
itself has no moving parts and is made of simple components.
In the glossary that follows, we begin our
discussion of the three basic types of filters - sand, diatomaceous
earth and cartridge by providing definitions for many of the terms
you'll encounter as we present a series of filter articles.
A guide to basic DE, sand and cartridge filter
usually made of zinc or magnesium, that pre-vents electrolysis
or galvanic action in steel filters.
||The process of
cleaning the filter medium and elements by reversing the flow
of water through the filter - and thereby flushing accumulated
debris out of the filter.
||A phenomenon in
DE filters in which the filter medium builds up between filter
elements, limiting flow.
||A filter that
uses replaceable paper or fabric-like cartridges as the
||A powder made of
fossilized skeletons of tiny plankton, called diatoms, that
serves as a filtration medium when it forms a cake on the
||A filter that
uses diatomaceous earth as the filtration medium.
line leading from the filter equipment to the pool or spa.
surface area through which water flows in the filter housing;
measured in square feet.
time between cleaning and backwash routines.
used to filter debris from the water - usually sand, a
cartridge or diatomaceous earth.
line that leads from the pool or spa to the filter equipment.
Also known as the suction line.
||A valve that
permits the multi-directional control of the flow of water
through a filter; it combines the function of two or more
in pressure between the influent and effluent lines of a
||The most common
type of filter; the water is forced through the filter by a
pump mounted on the influent side of the filter.
that measures the water pressure in influent and effluent
lines. An increase or decrease in water pressure indicates
either cleaning or backwashing operations or a plugged line.
||A filter that
uses graded layers of sand as the filtration medium.
||The part of the
filter element or grid on which the filter medium, usually DE,
is deposited or caked.
required to circulate a volume of water equal to the capacity
of a given pool or spa.
||A filter through
which water is pulled by a pump positioned on the effluent
side of the filter. Most vacuum filters use DE as the medium
There are three basic types of filters:
Diatomaceous Earth (DE), sand, and cartridge.
Earth (DE) Filters
This filter consists of a tank with a series
of fabric covered grids, also called filter elements. The fabric is
coated with a filtration substance media called DE, or diatomaceous
earth. DE is the fine ,white powder found in large deposits in the
ground. They act like filters by allowing water to filter through
while leaving the impurities behind. They are able to filter out
A filter must be properly sized to a pool or a
spa's circulation system. This size is determined by square footage
of surface area of the filter media, which equals to the total
square footage of the girds. A typical filter has eight girds that
total 24 to 72 square feet. The girds are placed into tanks that are
2 to 5 feet high and about 2 feet in diameter. Without the filter
girds, DE would turn into caked mass, when wet, making it impossible
for water to flow through.
There are two basic types of DE filters: the
vertical grid and the spin type.
Vertical Grid Filters
The grids in this type of filter are assembled
vertically on a manifold. A holding wheel secures the grids to the
manifold and retaining rod screws into the base of the tank to
secure the assembly. Water enters the tank at the bottom and flows
up and around the outside of the grids. It then flows down the stem
of each grid, into the hollow manifold, and out of the filter.
The spin filter is obsolete but still can be
found on older pool systems. The girds are wheel shaped and lined up
horizontally like a box of donuts. They operate in a similar manner
to the vertical grid filter, but to clean them, a crank is turned to
spin the grids. Although this is supposed to clean the grids, it is
not very effective.
Sand filters are 2 to 4 feet in diameter and
look like large balls. Older models generally are housed in metal
tanks. The sand in the filter strains out impurities as the water
pushes its way through. The water enters the top or side of the
filter through a multiport or piston backwash valve and sprays over
the sand. The sharp edges of the grains catch the impurities. The
water is pushed through the laterals and bottom manifold where it is
then directed out of the filter. The individual drains of the drain
manifold are called laterals. A drain pipe is located in the bottom
of the tank for emptying out the water when necessary.
The operation of a cartridge filter is similar
to that of a DE filter except there is no DE involved. Water flows
into the tank which houses one or more cylindrical cartridges of
fine, pleated mesh material. The tight mesh of the fabric strains
out impurities. Unlike the backwashing method used by DE and sand
filters, when it is time to clean the cartridges they simply are
removed and washed.
Selecting a good filtration system is the key
to healthy, clean and sparkling water in the pool or a spa. A filter
fits into the equipment sequence after the pump - so whether you're
replacing an old filter or installing a filter on a newly built
pool, you'll need to match the filter to the pump and the size of
To properly size and select the filter for a
pool or spa, you must first calculate the pool's volume and
capacity. Next, compute the pool/spa flow rate and the filter flow
rate. Once you've done all that, and have taken some other factors
into account, you'll be ready to select the right filter for the
system in question.
and Selection Techniques
Filter systems are required to meet Health
Codes for turnover rates and filtering capabilities in gallons per
square foot of filter area. For this certain criteria are to be
- Calculate The Volume
The first step in finding the correct
filter model is to figure out how much water has to be filtered.
Here are some simple formulas and techniques to use when
calculating the volume of a swimming pool:
For a rectangular pool, multiply the
length by the width by the average depth. For a circular pool,
multiply the radius by the radius by 3.14 (pi) by the average
depth. Oval pools are actually rectangles with semicircles on
the ends. These are not true ovals and require either combining
the formulas for circular and rectangular pools, or using the
using the grid technique.
Make a scale drawing of the pool on a
piece of square-grid graph paper, with each square representing
one square foot or any standard unit.
Then simply count up the number of
squares, not missing those partially filled squares making
complete ones, and that will give you a close estimate of the
pool's area in square feet. Multiply the area by the approximate
average depth of the pool gives you, the volume in cubic feet.
- Calculate The Capacity
Compute the capacity or the number of
gallons of water that the pool will hold. To calculate the
capacity, simply multiply the pool volume by 7.48 (the number of
gallons of water contained in a cubic foot of volume).
As an example, suppose you have a
rectangular pool that is 40 feet long and 20 feet wide, with an
average depth of 5 feet. Plug these numbers into the volume
equation and multiply: 40 x 20 x 5 = 4,000 cubic feet. Now plug
the volume into the capacity equation and multiply: 4,000 x 7.48
= 29,920 gallons. Simple.
- Calculate The Flow Rate
The flow rate is the volume of water
flowing past a given point during a specific period of time,
measured in gallons per minute (gpm) or gallons per hour (gph).
To calculate the flow rate, divide the capacity of the pool by
the turnover rate, which is the time required to circulate a
body of water equal to the capacity of the pool.
Let's say you want to set up the pool to
have an eight-hour turnover rate. Your success in achieving that
will depend to a large extent on which filter you eventually
install. Therefore, you must first determine the desired flow
rate - one that will facilitate the turnover you're seeking.
The equation to find the flow rate for the
29,920-gallon pool noted above (no matter what its shape) is:
29,920 -. 8 = 3,740 gph. To calculate the flow rate per minute,
divide the flow rate per hour by 60. In this case, 3,740 @ 60 =
62.3. That is the rate at which you want the filter to work.
Stating this situation another way, the
calculations for your 29,920-gallon pool show that you require a
flow rate of 62.3 gpm to filter the pool's capacity in eight
hours. Therefore, your goal is to determine which model of
filter will filter 62.3 gallons of water per minute - resulting
in a complete turnover every eight hours in the pool in
- Calculate The Filter Flow Rate
To achieve that goal, you have to find a
filter whose filter flow rate matches the desired flow rate for
the pool. The filter flow rate is defined as the amount of water
filtered over a given period of time - expressed in gallons per
To determine the filter flow rate,
multiply the filter area by the filter rate. The filter area is
the filtering surface area through which water flows in the
filter housing - measured in square feet. The filter rate is the
number of U.S. gallons of water that flows through one square
foot of effective filter medium per minute during the operation
of the circulation system.
If you didn't follow that, don't worry -
all you have to do is get both figures from the filter
manufacturers. In our example, let's say you have a filter area
of 5 square feet and a filter rate of 12.5 gpm. (These numbers
are based on a popular model of sand filter.) If you multiply 5
x 12.5 you have a filter flow rate of 62.5 gpm pretty darn close
to our desired flow rate of 62.3!
Now you'll need to consult filter
manufacturers to find a model with the necessary filter area and
filter rate. Once these numbers are provided by respective
manufacturers for various models, you can calculate the filter
flow rate to see which particular filter will match the need.
- Decide Which Type Of Filter You Prefer
What type of filter do you prefer: sand,
diatomaceous earth or cartridge? Pressure or vacuum filters?
From your poolside experience, you probably already have a good
idea of the type you like. You may even have narrowed it down to
a preferred manufacturer which will make it even easier to
perform your calculations and select a filter that will do the
The mathematical relationships between
filter area, filter rate and filter flow rate will remain the
same for any type of filter. Never hesitate to contact
manufacturers or their dealers to ask their professional advice
in this area.
- Make Sure To Oversize The Filter
When selecting the right-sized filter, it
is important to keep in mind that as the filter removes debris
from the water, the filter medium will become more and more
clogged, and the filter will require an ever greater flow to
clean an equal amount of water.
It is necessary, therefore, to select a
filter that is larger than indicated by our calculations of flow
requirements. This is especially true for commercial pools and
Using our example, you could either select
a model with a larger filter area or a model with an increased
filter rate. To allow for debris buildup and backwashing, you
might select a model with a filter area of 5 square feet and a
filter rate of 20 gpm. That gives us a filter flow rate of 100
gpm - well beyond our desired rate of 62.3 Alternatively, you
could choose a filter with 4 square feet of filter area and a
filter rate of 25 gpm per square foot.
- Limit The Filter Rate And Adjust The
In many cities and counties through-out
the country, filter rates on pools are regulated. The National
Sanitation Foundation sets maximum filter rates in order to
ensure effective filtration - since the faster the water passes
through the medium, the less effectively it is cleaned.
Filter-rate ceilings are imposed most
often for commercial facilities. You may have to compensate by
selecting a model with a larger filter area. By doing so, you
can achieve the same flow rate without exceeding the maximum
- Select The Correct Filter
Taking all the above calculations and
factors into consideration, you're now ready to select the
proper filter for a particular pool.
This process is used to clean DE and the sand
filters. The water is send backwards through the filter, flushing
the debris into a waste line or a sewer line. A backwash valve on
the filter reverses the flow of the water. There are two types of
backwash valves: the piston and the rotary (multiport is a variation
Water enters this type valve and is directed
to the filter in the normal operation. The water is then filtered
through the DE or the sand and return to the pool. When the handle
of the piston is raised into the backwash position, the piston disks
force the water into the filter tank through the outlet port. Thus
the backward flow of water through the filter, flushes debris and
dirt out of the tank and out of the valve inlet port. Once inside
the valve again, the waste water is directed to the waste port.
Never change the piston position when
operating the pump. This puts too much pressure in the pump, motor,
and the valve O-rings and may result in leaks. The piston type
backwash valve usually is located on the side of the filter tank.
The rotary backwash valve is used exclusively
on vertical DE filters. The water direction is changed by rotating
an internal rotor located below the filter tank. A rotor gasket seal
or O-rings prevent the water from leaking. A retainer ring holds the
valve body to the underside of the tank with bolts that pass through
the bottom of the tank.
To backwash, rotate the rotor 90 degrees.
Water enters through the middle and up the inside of the grids. The
DE and dirt is washed off the grids as the water flows from inside
the grids to the outside. The water is then flushed back through the
rotor and directed to the opening marked "backwash". Do
not rotate the rotor while the pump is running for leaks may occur.
The multiport backwash valve is used on sand
filters and looks like a rotary valve when taken apart. Sometimes
mounted on the side but usually mounted on top of the filter tank,
this valve offers more than one choice for water flow direction.
After the pump backwashes, clean water rinses out the pipes before
returning to normal circulation. This prevents debris from returning
to the pool after a backwash has been done.
Regardless of the valve used, if the backwash
discharge port is not plumbed directly to a drain or sewer line, a
hose has to be attached to direct the dirty water onto the lawn or
into the street (if permissible). The normal hose usually is 1 1/2
to 2 inches in diameter and made out of inexpensive, collapsible
plastic. Backwash hoses are available in various lengths up to 200
feet. The pool vacuum hose can be turned into backwash hose by using
a hose clamp.
Gauges and Air Relief Valves
Most filters are fitted with a pressure gauge,
mounted on top of the filter. Sometimes the gauge is mounted on the
multiport valve. These gauges read 0 to 60 psi and are useful in
several ways. When the pressure goes beyond 10 pound over the normal
operating pressure it is time to clean the filter.
The pressure gauges spot the operating
problems in the system. If the pressure is lower than normal, it
indicates that there is obstruction in the water that is coming into
the filter; and when the pressure reads high ,then the filter is
dirty or there is some obstruction in the flow of water after the
filter. When the pressure fluctuates while the pump is operating ,
the pool or the spa might be low in water or have some obstruction
at the skimmer. This shows that pressure gauge is an important
instrument on the filter.
For commercial pools or spa ,some codes
require a pressure gauge be mounted on the incoming pipe and on the
outgoing pipe to compare the difference. The health department
inspector checks the cleanliness of the filter system by comparing
the two pressure readings. Normally the differential should be 2 to
An air relief valve is mounted on the T
fitting along with the pressure gauge. When a system first starts
up, or when it has lost its prime, there is lots of air in the
filter. An air relief valve allows air to escape from the filter,
when its plug is loosened. Thus air relief valve is important if the
filter is to work to its full filter square footage.
Sight Glasses are the clear section of the
pipe, that are normally installed on the backwash line coming out of
the backwash valve. They can be installed anywhere in a line of pipe
where you want to see the effectiveness of cleaning action. When
installed on the backwash line and when the water is going directly
into the drain, the sight glass helps to see the dirty water
becoming clean and time to stop the backwash.
Repair and Maintenance of filters consists of
installation, plumbing, cleaning and troubleshooting.
of Pool and Spa Filters
Installing a pool filter is a fairly
straightforward process, but it always requires care and the
faithful following of a few basic rules. The text below covers those
basics, but before you start cutting PVC and lubricating O-rings,
remember that this is a generic guide and that you should always
consult manufacturers' literature before working with any unfamiliar
Beyond that, once you survey the situation by inspecting the
equipment pad, the plumbing design and the electrical system, you
should be ready to go.
Sizing up the task at hand
When it comes to filters, some of the most
fundamental considerations can make the biggest differences. Where
the unit is located, how neatly it is incorporated into the overall
circulation system and how it's tied into the pool's electrical
circuitry are all very important.
Equipment pad: The equipment pad should
be a flat, level slab of poured concrete, brick or concrete block.
Never install a new filter on wood, because it can warp or decay
beneath the filter's footings and compromise the position of the
unit. Three things to watch: First, filters should always be
installed on a level surface; if things aren't square, the unit may
vibrate or operate to less than its optimum ability. Second, filters
should be located as close to the pool as possible. Third, the
filter should have adequate drainage and should be positioned to
provide plenty of room for service access and maintenance.
Plumbing: The plumbing should be
designed and installed with the shortest lines and the least number
of fittings needed to achieve optimum water flow efficiency in the
circulation system. If the filter is most conveniently installed
away from the pool, however, increasing the pipe size between the
filter and the pool will decrease the head resistance and compensate
for a longer run. Inspect the plumbing so you can be prepared with
the proper fittings and materials.
Electrical hookup: Although the filter
is not directly connected to electrical power, the pump motor runs
on electricity, which means that the filter must be grounded and
bonded by a professional electrician. In addition, the electrical
wiring and hookup of the motor must have been completed by a
professional electrician in accordance with local and national
Down and dirty
Now that the pad is ready for the new filter,
it is especially important to refer to the filter manufacturer's
installation manual for specific instructions regarding the
particular make and model of the filter you're installing. Once
you've finished your reading, the first step in the installation is
to place the filter on the pad. You might consider bolting the unit
to the pad, although relatively few filters are mounted in this
Next, connect the circulation plumbing to the
filter. Every filter has two basic plumbing connections - the
influent and the effluent lines. The influent line supplies water to
the filter; the effluent line provides an outlet for water after it
passes through the filter. A gate valve should be installed on both
the influent and effluent lines. This will permit you to close the
lines when it is necessary to service, remove or replace the filter.
The plumbing lines are connected directly to
the filter's multi-port valve either by hand-tightened union
connections or, if appropriate, by bonding with an adhesive, such as
a PVC cement. For threaded pipe connections, the application of
PTFE tape to the threads before connecting the pipes is often
Be sure the O-rings on all valve fittings are
clean and that each O-ring and O-ring groove is lubricated with
silicon lubricant. Install O-rings in their grooves and tighten with
the appropriate union collar. Before applying any adhesive, be sure
all connecting points are clean and dry - and use the recommended
primer before doping PVC components.
Allow an appropriate drying period before
pressure testing or operating the equipment - and take into account
the fact that temperature and humidity may affect the drying time of
Once the filter is installed on the pad, all
of the plumbing connections are set and the unit is properly
grounded, it is time to put the circulation system into full
operation. The three main types of filter - sand, DE and cartridge -
require different start-up procedures. As above, the following are
general guidelines for your reference; manufacturers' manuals will
give you the specific help you need.
Sand filters: Most sand filters in use
today are high-rate models in which water typically passes through a
number of layers of sand and gravel that have been carefully placed
in the filter tank.
The size of the sand particles used as the
filter medium is very important for optimum efficiency. If the sand
granules are too big, filtering efficiency is decreased; if the sand
particles are too small, the filter will clog up quickly.
Check the specifications provided by the
filter manufacturer, then fill the tank with layers of coarse,
medium, and fine gravel followed by the silica sand layer on top as
directed. The silica sand commonly used as the top layer has a
diameter between 0.35 and 0.45 millimeters with a typical uniformity
coefficient of 1.4. Also, plan to leave a space between the sand bed
and the overdrain. This space is known as freeboard, and most
manufacturers suggest it should amount to half the depth of the
While most sand filters use several layers of
material to clean the water, some models use only one or two
Flocculents are often used to improve the
performance of sand filters. Most filter flocculents are alum based
preparations that form a gelatinous layer on the top of the sand. As
an alternative, diatomaceous earth can be used: Add one-half cup of
DE for each three square feet of filter area after the unit has been
filled with sand.
DE filters: These units filter water by
passing it through a layer of diatomaceous earth that coats grids
inside the filter tank. The DE is added as a precoat to the grids,
attaching itself on the grid-covering mesh known as the septa.
Common practice calls for adding two ounces of DE per square foot of
filter area, with a typical variation of a half-cup either way
depending on manufacturer specifications.
The DE should be mixed with water and fed into
the filter as a "slurry," or suspended mixture. After
turning on the circulation system, add the slurry via the skimmer at
as steady a rate as possible to permit even coating of the filter
septa. Ideally, the DE will form a uniform "cake" between
1/16 and 1/8 of an inch thick.
DE can also be introduced to the filter by
using a precoat pot, solution feeder or erosion feeder that is
specifically designed for precoating.
Cartridge filter: Setup of cartridge
filters is simple: Insert the filter cartridge per instructions and
fire up the circulation system. You can also use a flocculating
agent for cartridge filters.
With all types of filters, open the unit's air
release valve and turn on the pump. When a steady stream of water
shoots out, close the valve. Manufacturers urge technicians and
homeowners always to remember to open the air release valve when
starting the filter, because air pressure in a filter can be very
Although we're covering it last here, safety
should be a primary consideration in filter replacement and repair -
particularly with units outfitted with pressure-clamp assemblies,
which, under certain conditions, can fly apart with tremendous
force. In fact, flying parts from a "blown" filter are
often the source of severe property damage and, unfortunately, the
cause of severe, sometimes fatal, injuries.
Filter manufacturers often recommend
tightening the clamp to specs using a torque wrench. Extra care in
placing the assembly around the tank and tightening is critical,
they say, with some recommending partial tightening of the clamp and
then tapping the assembly into place around the perimeter of the
Improper application of the clamp assembly may
result in a poor seal that could cause the filter to blow.
Alternatively, the uneven seal might slowly force the tank out of
round over time and create serious problems in future servicing -
and further increase the chance of blowout.
A final safety tip: Whenever
any repairs are done on a filter or related components, cut off all
the pool's electrical circuits at the source!
Diagnostics and Troubleshooting
A pool filter's water-cleansing function is
pretty straightforward, but small problems can become big service
hassles if you let them get out of hand. Here's a handy trouble
When a filtration system goes awry, the
quality of the water can deteriorate quickly Poor filtration leads
to increased chlorine demand and chemical costs.
The following outlines basic filter problems,
defines probable causes and suggests solutions. For the most part,
these discussions cut across all filter types - diatomaceous earth,
sand and cartridge. Please note that these guidelines are for
general information only; you should always consult manufacturer
literature for specific recommendations and operating guidelines for
each filter model.
Before you start, note this general rule: When
checking an operating filter's performance, tap the face or casing
of the pressure gauge firmly to make sure the needle is not
sticking. A gauge that fails to indicate a rise in pressure not only
compromises your ability to monitor filter cycles, it can also be
quite dangerous: Excessive pressure can result in cracking of the
filter body or failure of the clamping device on the filter tank.
Symptom: Reduced flow of water through the
As dirt accumulates on the filter media, water
flow is restricted - and pressure within the tank rises. When the
pressure rises to a level specified by the manufacturer, it's
usually time for routine backwashing of a sand or DE filter, or
simple cleaning of cartridge filter elements.
The ranges of operating pressures for filters
vary widely, depending on type. A typical range for high-rate sand
filters, for example, may be 10 to 15 pounds per square inch at the
beginning of the filter cycle (that is, the period between routine
backwashings or cleanings) on up to 25 to 30 psi when backwashing is
Conveniently, some filter systems - mainly
large high-rate sand or diatomaceous earth filters on large
commercial installations - have pressure gauges installed on both
the influent and effluent lines. As the media becomes clogged with
dirt, the influent pressure will become higher than the effluent
reading. When the differential between readings reaches a specified
level, it is time for backwashing.
Gradual pressure rises are normal in the
course of the filter cycle, if the rise in pressure is relatively
consistent, then normal backwashing or cleaning routines will
suffice. If pressure begins to rise more rapidly than normal,
however, it is time to take a close look at the elements of the
Symptom: Short cycle between backwashes.
Most often, short filter cycles indicate
excessive flow rate through the filter. This indicates in turn that
the filter may be undersized or that the pump may be too powerful
for the system. Install a properly sized system.
In other cases, short filter cycles indicate
an unusual increase in the burden on the filter media caused by
excessive dirt, debris, body oil, lotions, hair or algae. Very high
bather loads, lead to overworked filters.
Now for more specialized problems:
With sand filters - and DE filters to a lesser
extent - you can get into trouble when soda ash or coagulants are
fed into the skimmer too fast. In these circumstances, the chemicals
do not have sufficient opportunity to dissolve and, instead of
passing through the bed in solution, clog the media and raise the
pressure. It is best to introduce these agents more slowly or
dissolve them before introducing them to the skimmer.
Note: Alum should never be
used with a DE filter: It will only solidify the filter cake.
In addition, clogging of the septa in a DE
filter - whether by rust, calcium build-up or soda ash - may
increase the pressure and compromise effective filtration. If you
suspect this problem, clean the filter elements and check for
clogging of the fine nylon mesh covering the septa. Treating the
septa to a light acid wash and hosing with a strong stream of water
will usually relieve the problem.
Symptom: Inadequate filtering action.
All of the troubleshooting tips in this
category refer to specific filter types.
In a sand filter, if the media has been
charged improperly or in adequate quantities, channels may have
formed in the sand and gravel bed, and may be allowing water to pass
through unfiltered. Look for evidence of channeling or tunneling and
recharge the filter if necessary.
Also in a sand filter, if the unit has not
been backwashed consistently, mud balls may have formed on the
surface of the sand bed, thereby limiting filtering action. Or, in
extreme cases, the sand may have calcified and will no longer filter
out dirt. Look for mud balls or evidence of calcification; backwash
or remove the old sand and recharge the filter as necessary. Filter
sand should normally last four to five years.
Moving to DE units, poor filtration often
results from coagulation or solidification of the DE. If you observe
hardening of the DE cake, remove and clean the elements as per the
manufacturer's instructions and recharge the filter with fresh DE.
If DE is fed to the unit by a slurry feeder,
the unit may not be feeding enough DE into the filter to adequately
coat the septa. Conversely, an inconsistent filter cake may result
from feeding DE too quickly into a skimmer when recharging the
system. The trick here is to observe DE introduction rates and
adjust them as needed.
More can go wrong in coating a DE filter: If
you have an over-rated DE filter or an under-rated pump, for
instance, there may be inadequate pressure within the filter to
properly coat the septa. Here, you need to check the manufacturer's
specs and replace equipment as needed.
Backwashing should be performed frequently
enough and for adequate periods when it is performed, for media to
be cleaned sufficiently.
It also pays to watch out for inadequate or
plugged backwash lines that might not be allowing sufficient flow
out of the filter during backwashing. If a portion of the backwash
discharge is retained in the tank because of inadequate flow, the
backwash line will clog over time with caked media. To address this
possibility, check the lines for clogs and clear as necessary.
Last but not least, a specific tip for
cartridge filters: Poor filtration without a rise in pressure may
indicate torn or worn out cartridges that are simply allowing water
to pass through without filtering. Replace these cartridges as
Symptom: Low flow rates in the system.
A flowmeter is a handy diagnostic tool in
evaluating filter performance. If you get a low reading with a
flowmeter but a high reading on the pressure gauge, something is
restricting the flow - most likely a blockage in the piping, or,
possibly, under sizing of the entire piping system.
As a rule of thumb, the maximum flow rate
through a 1-1/2-inch PVC pipe is 70 gallons per minute. Through
2-inch plumbing, it should be 110 gpm. These figures are based on a
standard hydraulic specification of an eight feet-per-second maximum
A drop in the return flow may be traced to a
clogged pump strainer basket or skimmer basket. The remedy here is
simple: Clean the baskets.
If both flow and pressure readings are low,
the pump may be undersized - or you may have a plugged pump impeller
or lint trap. It is important to note that pump or motor trouble can
lead directly to filtration problems.
Symptom: Sand or DE entering the pool.
The first suspect with sand- or DE clouded
water is the backwash valve. If it is left in an intermediate
position, media can flow back into the pool. If this obvious answer
doesn't suffice, you'll need to look for solutions inside the tank.
With sand filters, broken laterals are a
common culprit here - and replacement is the only solution.
In a DE filter, torn or worn out septa will
let DE flow into the pool.
Symptom: Air pressure build-up.
Air present in the filter tank may allow some
of the filter media to be forced into the pool and can otherwise
compromise filtering action. In sand filters, it's a prime suspect
in channeling; in DE units, it may disrupt the filter cake.
Air pressure build-up in a filter is
dangerous. If you have a problem with air in the tank, check for any
hairline cracks or leaks in plumbing connections on the suction side
of the pump. A low water level in the pool is another suspect: Air
may enter through the skimmer.
It is always important to release any air
present in the filter tank. Not only will the presence of air
inhibit good filtration, it can also increase the danger of the
filter tank suddenly cracking by rapidly increasing pressure within
Air is easily released by opening the pressure
release valve and allowing the air to escape. When a steady stream
of water comes out of the valve, then you have released all of the
If you are unable to perform immediate repairs
on a sand or diatomaceous earth filter equipped with a multiport
valve, the following tip may come in handy:
Manual feeding of chlorine or other sanitizers
will maintain clean water for seven to 10 days, depending upon
bather load and other such factors. Experts suggest you turn the
multiport valve to the "recirculate" position, which will
keep the skimmers working as well as the automatic chlorinator, if
the pool is equipped with one. The water clarity may suffer a bit,
but with sufficient sanitizer, it should not turn cloudy or green.
The nylon mesh on the septa can be repaired,
depending on how large a hole or tear is present. Also check the
points where the mesh is sewn to the frame of the grid: Even slight
unraveling or separation will allow DE to enter the pool.
D.E. Filters Troubleshooting
When it's time to work on a diatomaceous earth
filter, here's a guide to minimize the toil involved in tearing down
a typical D.E. unit, cleaning its grids and then recharging it to
keep a pool's water sparkling clean.
Diatomaceous earth filters perform the same
water cleaning function as sand and cartridge filters, doing their
job with great effectiveness so long as too much dirt and debris
haven't built up to clog the system. At cleaning time, however,
differences among these filter types become amply apparent.
Unlike a cartridge filter, which requires
simple hosing off, soaking or routine replacement of cartridge
elements, or a sand filter, which for the most part requires only
periodic backwashing, a D.E. filter needs to be taken apart, cleaned
and recharged at least once each year. And it's a dirty job, no
matter how much it helps ease the overall pool-maintenance task.
- Release the pressure from the filter tank.
- Before taking the unit apart - and with the pump turned off -
open the filter's air-release valve. Wait a few moments as air
is drawn in and water flows out of the tank: When the hissing
stops, you can get to work.
- Mark the lid, unscrew the, clamp ring and
remove it from the tank. - After marking the tank on the top and
the bottom with a grease pencil, unscrew and remove the clamp
ring. The marks will help you align the two sections when
reassembling the filter
- Remove the top of the tank and pull out the
grids. - Using leverage if necessary - but being sure not to
bend or otherwise distort the tank in the process - carefully
remove the tank's lid. Now pull the grid assembly from the tank,
making certain you don't break any of the manifold fittings or
cut the grid fabric on any sharp edges in the vicinity. Note:
Lifting the grids may require a good bit of muscle, so be sure
to exercise care to avoid back injury.
- Hose off the grids. - Using a pressure
nozzle, make sure all of the old D.E. is thoroughly cleaned from
the grid fabric. Dispose of the spent D.E. in accordance with
local health department standards.
- Inspect the manifold and grids. - If it
becomes necessary to check the manifold and grids for suspected
damage, carefully remove wing nuts with a pair of pliers, taking
precautions not to strip the threads. Inspect the grids for
small rips or holes. Note: you can temporarily patch most grids
with PVC pipe adhesive.
- Clean the filter tank. - Release the tank's
bottom drain and let the remaining water run out. Hose as much
of the loose D.E. and debris out as possible. Note: A pair of
channel locks or pipe wrench can help with sticky bottom drain.
- Inspect the inside of the band / ring. -
Use a screwdriver to free the band ring from the tank and
inspect it for wear. Clean it thoroughly with water or, if
grease or other lubricants have been used previously, clean it
with soap and water. Put the band ring back, making sure that it
is seated evenly and securely in place.
- Inspect the 0 ring. - Check the ring for
wear and replace it if necessary.
- Put the grid assembly back in place. -
Return cleaned grids and their assembly to the tank, making
certain all grids are properly aligned and that the pipe
fittings are securely in place as needed.
- Place the lid back on the tank. - Return
the lid to the tank, realigning it with the grease pencil marks.
Put the ring clamp back on the tank, making sure it is seated
properly all the way around the tank.
- Tighten the bolt on the clamp assembly. -
Using an open-end wrench if necessary, tighten the bolt on the
clamp assembly, occasionally tapping the band ring to make
certain it is seating itself properly. Follow the manufacturer's
recommendation with respect to how tight a fit you need.
- Recharge the D.E. - Restart the pump,
keeping the air-release valve open until a steady flow of water
emerges. Place an appropriate quantity of D.E. in a bucket, then
add water to make a slurry. Note: Make the slurry thin
enough so that it can be poured slowly into the skimmer and pour
it only with the pump on. As an option, scoop cups full of dry
D.E. into the skimmer, allowing it to mix with the water and
circulate into the filter.
- Watch the pressure gauge. - After adding
the D.E. to the skimmer, mark the pressure reading down on the
tank with a grease pencil. At subsequent stops, you will be able
to tell at a glance how much the pressure in the tank has
increased. Now all you have to do is hose down the area and head
to your next assignment.
Cartridge filter maintenance
The basic design of cartridge filters makes
them easy to service. Here's a step-by-step guide to getting the job
Servicing cartridge filters is simple. All
there is to it is simply removing the cartridge elements, soaking
them, hosing them off and putting them back in place. In fact, if
there is any burden placed on service routines by cartridge filters,
it's because cleaning or replacement are the only options for
Unlike sand or diatomaceous earth filters,
cartridge filters cannot be cleaned by backwashing. This difference
makes it important to stay on top of your filter maintenance
routines with cartridge units.
As with all types of filter media, you can
determine the need for service with cartridges by watching the
pressure rise. When it is 8 to 10 psi above the baseline it is time
to service the filters.
Because thorough cleaning typically requires
overnight soaking, you also need to consider what to do without the
equipment in the meantime. You can either leave the system off, or
you can replace the elements, if you are a technician, at each
cleaning and rotate elements from the filter tank to the soaking
bucket. As always, consult manufacturer literature for specific
maintenance procedures and take care to release air pressure from
the system when restarting the circulation system.
- Remove the lid - With the pump turned off
and the pressure-release valve open, unscrew or otherwise loosen
the clamp fitting and remove the tank's ring-clamp assembly. To
remove the lid or the upper half of the tank, apply leverage to
the lip of the lid and carefully remove it, making sure not to
force the lid out of round.
- Remove the cartridges. - You can either
remove the cartridges one at a time or all at once. To remove
the cartridges one by one, unscrew the wing nuts and lift the
cartridges out. If you need to pull the entire
cartridge/manifold assembly, consult the manufacturer's
literature, typically, this method is used only if you suspect a
leaking manifold and are removing the assembly for inspection.
- Soak the cartridges. - Place the cartridges
in a special cartridge-soaking solution or a solution of water
and trisodium phosphate (TSP). Use approximately three cups of
TSP in a 32-gallon drum or a water tight plastic trash barrel.
- Rinse off the cartridges. - After soaking
the elements for 1 to 3 days, rinse them off using high-pressure
- Inspect the cartridges. - Check the
cartridges for damage such as large tears or holes that would
compromise filtration. The cartridges should return to their
original white or light gray color when properly cleaned.
- Replace the cartridges. - Return the
cartridges to their assembly, making sure they are carefully
seated on the manifold fittings. Reapply the wing nut or
fastening device. If you are returning the entire assembly to
the tank, it may be more convenient to assemble the unit outside
the tank. Follow manufacturer directions and make sure the
manifold is properly connected to internal fittings.
- Inspect the 0 ring and ringclamp assembly.
- Inspect the 0 ring for wear - and replace it at the first sign
of deterioration. Clean the ring clamp and lip of the lid if
- Replace the lid - Firmly seat the lid by
applying manual pressure. Leaning on the lid may help, but take
care not to warp the tank or the lid as you press down.
Carefully replace the clamp ring making sure that it is properly
placed. Tighten the assembly to manufacturer specifications.
As with all filter systems, before you start
the pump, make sure the air-release valve is open and wait for
emergence of a stream of water.
Sand filters maintenance and
Sand filters clean pools gradually, removing
dirt, debris and particulates as water passes through a deep bed of
sharp sand. With the kind of proper charging and maintenance
described in this article, these filters will deliver years of
Backwashing is the regular service for
high-rate sand filters. Unlike diatomaceous earth or cartridge
filters - which must be opened for periodic cleaning and replacement
of media - a sand filter can go almost indefinitely without needing
The basic physics of sand filtration are also
different from rival filter varieties: High-rate sand filters clean
water via a process known as depth filtration, meaning that dirt
penetrates the sand bed and is captured in the tiny spaces between
grains of sand. By contrast, dirt and particulates are captured on
the surface of the media in both cartridge and DE filters.
The depth-filtration principle works just fine
- unless, that is, the sand filter is not backwashed often enough.
Without backwashing, dirt particles begin to accumulate on the
surface of the sand bed and will result in short cycles, channeling,
and poor overall filtration.
Conversely, if you backwash too often, you
will also compromise filtration: When the sand bed is totally clean,
some of the smaller particles of dirt will pass through unfiltered.
As the bed begins to accumulate dirt, the filter begins to catch
those smaller particles. In other words, getting ahead of yourself
by cleaning the media too often will prevent a sand filter from
doing its job.
When to Backwash
How do you know when it's time to backwash?
One obvious cue is cloudy water: When the pool
gets murky, a dirty filter is the prime suspect. Another, far better
cue, however, can be found with the filter's pressure gauge or
If the system has both inlet and outlet
pressure gauges, you will note only minor pressure differentials
-perhaps 3 psi - when the filter media is clean. As the sand bed
begins to load up with dirt, that differential will begin to
increase. In most high-rate sand filters, it's time to backwash when
the pressure differential reaches 18-20 psi.
If the system has an inlet pressure gauge
only, you should backwash when the pressure increases by 8-10 psi
from initial post-backwash readings. The best idea here is to mark
the pressure gauge with a grease pencil right after a good
backwashing - or to maintain a record of the running pressure on a
route sheet as you monitor filter cycles.
These filter cycles can be affected by many
different factors, ranging from heavy bather load and algae to
wind-blown dirt and debris. In addition, a sand filter on a newly
plastered pool will clog quickly with plaster dust, which often
precipitates out of new plaster during start-up procedures.
This fine plaster particulate can easily clog
a sand bed and greatly reduce the length of initial cycles. In fact,
when first starting a sand filter on a fresh pool, it may be
necessary to perform an extended backwash of two to three times the
normal duration to rid the sand bed of the bothersome dust.
Routing the flow
Backwashing is a simple matter of reversing
the flow through the filter by sending water up through the
underdrain or laterals and diverting the outlet water to waste.
The procedure is simple: Turn off the pump to
avoid damage to plumbing or valving, then turn the control valve to
the backwash position and restart the system. Once the filter has
been backwashed for the desired time, shut the system down and reset
the valves. Don't fire up the system right away: The sand bed needs
time to settle back down into place.
When you restart the pump, a small burst of
cloudy water may enter the pool. This is typically caused by a
residue of backwash effluent present in the sand bed as a result of
inadequate backwash time. Some valve arrangements dodge this problem
by sending a small initial burst of water to waste before returning
filter effluent to the pool.
Given a typical flow rate of 15-20 gpm per
square foot of filter area, most manufacturers recommend backwashing
for 2-3 minutes. As always, it's a good idea to consult manufacturer
service manuals for specific backwashing procedures.
Putting Sand to Bed
The beauty of a sand filter is that the sand
itself acts as a permanent medium: Once it's charged you will rarely
- if ever - need to replace it. The keys to that longevity are
steady backwashing routines, as described elsewhere in this article,
and getting the system off to a good start with proper charging.
Here are the basic steps:
- First, obtain sand of the proper size. Most
sand filters use filter sand, which is typically .45-.55
millimeters in diameter. It is also commonly referred to as
"pool grade #20 silica sand." Note: some filters also
use gravel in the filter bed. Consult manufacturer literature
for proper gravel specifications.
- Next, to keep sand out of the circulation
system, cover vertically exposed plumbing or standpipes with
some type of protective cap. On some models, you also will need
to position the lateral assembly in the tank before adding the
sand to ensure that internal plumbing seats properly when the
valve at the top of the filter dome is reassembled.
- Just before adding the sand, some
manufacturers recommend filling the bottom of the tank with a
few inches of water to act as a cushion for the sand as it is
poured into the tank. This will help prevent damage to the
- Pour the sand gently through the top of the
filter tank. Although different models require varying amounts
of sand, a good rule of thumb is to leave 10-12 inches of
freeboard - that is, the space between the top of the sand bed
and bottom of the diffuser assembly. Adequate freeboard will
prevent sand loss during backwashing. Conversely, if the sand
bed is too shallow, the filter will work but will load with dirt
quickly and require frequent backwashing. Service and
installation manuals offer various tips to help you charge the
filter. Some, for instance, recommend holding down the vertical
standpipe to make sure it isn't dislodged as the sand is being
- Remove the protective caps and replace the
top valve or dome on the top of the filter tank. Some assemblies
are threaded into the top of the tank, while others are held in
place by a clamp assembly. All assemblies use O-rings to create
a good seal, with manufacturers typically recommending use of an
appropriate O-ring lubricant to ensure a good seal.
During the backwashing cycle, the sand bed in
a high-rate filter will actually rise up several inches in the tank
as the water scrubs dirt from the sand.
This is what happens inside the sand filter:
- This is a typical sand filter in the
filtration mode or cycle. The flat surface of the sand bed
indicates proper pump and filter sizing, which provides maximum
filter efficiency without channeling.
- As the backwash cycle begins, the sand bed
rises evenly in the tank as a result of proper flow rate through
- Within 2-3 seconds, the sand bed becomes
semi-fluid. At this point, dirt and other solids break free from
the media and are being discharged to waste.
- Within 5-10 seconds, the sand bed is now
totally fluid. Note the 6-7 inches of "freeboard"
between the top of the sand and the bottom of the diffuser. If
the pump and filter are properly sized, the sand will not rise
too high in the tank.
- Now in the "rinse" mode, the sand
bed is beginning to re-settle.
- The filter has now returned to the normal
filtration mode. A critical factor in this simple operation is
remembering to shut the pump down before changing the filter's
valves from one mode to another. Forgetting to turn off the flow
could result in damage to the valve and/or the filter.
Cleaning and Media Replacement
Keeping the filter clean is the simplest way
to ensure the other components work up to their specifications and
you end up with a clean pool. Let's review the process for cleaning
each type of filter.
Backwashing a DE filter as a regular practice
will backwash some dirt and some DE are flushed from the filter. The
remainder drops off the grids and falls to the bottom of the filter
in clumps. The manufacturers say that after backwashing 70 percent
of the DE has been removed, so you need to replace that amount. If
you add too little, the filter grids will quickly clog with dirt and
the pressure will build right back up, even stopping the flow of
water completely. If you add too much, you will get the same effect
by jamming the tank with DE.
Backwashing cannot remove oils from the grids,
which get there from body oil, oil in leaves, and suntan lotions.
Backwashing a DE filter is useful when the
pool has been trashed by winds, mudslides, algae, or other heavy
debris. You start to vacuum it and quickly the filter can't hold any
more dirt. To save a lot of time you backwash, add a little fresh
DE, and get on with the job. You repeat this process until the big
mess is cleaned up, then you break down the filter and clean it
The other time you might backwash is when
you're vacuuming a normally dirty pool, but the filter hasn't been
cleaned in awhile and is just about full of dirt. You're getting no
suction because the filter is clogged. Backwash, add some fresh DE,
finish cleaning the pool, and then do a breakdown and clean the
When the water is going inside the grid and
flowing outward, any debris in the water from the pool will clog the
inside of the grids (or laterals on sand filters), rendering them
useless. On a new pool startup where a lot of plaster dust or gunite
debris might be in the water, don't backwash. if you must, open the
strainer pot and turn on the pump. Flood the pot with water from a
hose and backwash as needed that way. Obviously, never vacuum a pool
with the filter on backwash because the dirt and debris you vacuum
will flow directly inside the grids (or laterals).
This get you to break down (or tear down) and
cleaning of a DE filter. The Purex/Hydrotech style of vertical grid
tank DE filter type is explained here. They are common in the field
and if you can do these, you can do them all.
- Turn off the pump and switch off the
- Open the tank drain and let the water run
out. Remove the lid of the filter. On some filters, it is as
easy as removing the clamping ring and applying light pressure
under the lid with a screwdriver. Some filters make such a tight
seal with the O-ring and lid and as the water is drained out, it
sucks the lid on even tighter.
- Remove the retainer's wing nut and remove
the retainer. Now gently remove the grids (elements). One design
flaw of many grids lies in the fact that they are made like
small aircraft wings-large, curving units-but they are set into
the manifold on stubby little nipples. Applying a reasonable
amount of force on the rather large wing part of the grid won't
hurt it, but the resulting torque on the flimsy nipple will snap
it right off. Therefore, to remove the grids, wiggle them gently
from side to side as you pull them straight up and out. Be
prepared to hose out the tank while the grids are still in place
(if the drain hole isn't also clogged with DE) or patiently
excavate the dirt and DE until you can free the grids.
- Remove the retaining rod by unscrewing it
from the base of the rotary valve. Sometimes it is corroded in
place, so have pliers handy to grip the rod and unscrew it. A
word of caution-the rod might be corroded enough that if you
force it with your pliers, it snaps off at the bottom, leaving
the threaded end in the rotary valve.
- Reach in the tank and remove the manifold
from the rim of the rotary valve.
- Hose out the inside of the tank, the
manifold, and the holding wheel. Hose off the grids and scrub
them lightly to loosen the grime. If the grids are still dirty,
soak them in a garbage can of water, trisodium phosphate (1 cup
per 5 gallons of water), and muriatic acid (1 cup per 5
gallons). After 30 minutes, try scrubbing them clean again.
Don't use soap.
- Inspect the manifold for chips or cracks.
DE and dirt will go through such openings and back into your
pool. Cracks can be glued. If chunks of plastic are missing, buy
a new manifold. Particularly inspect the joint between the top
and bottom halves of the manifold. These two parts are glued
together, tend to separate. Replace the manifold as you took it
out. Reinstall the center rod.
- Carefully inspect the grids before putting
them back inside. Look for worn or torn fabric, cracked necks on
the nipples, or grids where the plastic frame has collapsed
inside the fabric. Replace any several damaged grids. When you
reinstall the grids, notice that inside each hole in the
manifold is a small nipple and on the outside of each grid
nipple is a small notch. By lining up the nipple and notch as
you reinsert each grid, the grids will go back as intended. Now
lay the retainer over the tops of the grids and spin it around
until it finds its place holding down and separating the grids.
Screw on the wing nut and washer that holds down the retainer
- Get the lid back making sure the 0 ring on
the tank is free of gouges and has not stretched. If it is
loose, soak it for 15 minutes in ice water and it might shrink
back to a good fit. If not, replace it. Apply tile soap as a
lubricant to make it slide on easier (or silicone lube if you
can afford it) to the inside of the lid around the edge that
will meet the O-ring. Don't use Vaseline or petroleum-based
lubricants because these will corrode the O-ring material.
- Now close the tank drain, turn the backwash
valve to normal filtration, and turn on the pump. Let the tank
fill with water. Turn off the pump and turn the valve to
backwash. The water will drain out, sucking the lid down. Don't
be afraid to help it along by getting on top of the lid. Your
weight will finish the job.
- Replace the clamping ring, return the valve
to normal filtration, and start the pump/motor. Open the air
relief valve and purge the air until water spurts out the valve.
- Never run a DE filter without DE, even for
a short time. Dirt will clog the bare grids. Remember, it's not
the grids, but the DE that does the actual filtering. The label
on the filter will tell you how much DE to add, or refer to the
table on the bag of DE. It tells you how many pounds of DE to
add per square foot of filter area.
DE is added to the system through the skimmer.
Do not dump it in all at once. It will form in clumps at the first
restricted area, like a plumbing of elbow or the inlet of the filter
tank, or even crystallized it and make it hard. Sprinkle a little
amount at a time, mixing it in the skimmer water with your hand.
This will disperse it evenly in water. If the the unit is not
assembled correctly, DE will flow back into the pool after passing
through the unit, when you start up the unit. If the water has
slight milky residue, which reduces with more flow of water then it
is normal and there is nothing wrong in it.
Most of the pool have skimmers where you can
add the DE. But if there is no skimmer than, make slurry of DE in a
bucket turn on the pump and add it to the strainer pot, followed by
clear water. This way the DE will coat the gird evenly. Cover the
strainer and reprime the pump.
Sand filters use specific size and quality of
sand (#20). If the particle size is big then the filtration of
smaller particles is not possible and if the sand size is too small
then it will clog the laterals.
Sand filter need regular backwashing that are
effective. When the tank is full of circulating water the sand is
suspended in the tank. The sand is light enough to stay floating in
the tank, but heavy enough that it does not flow out with the
backwash water. This is why the multiport valve is located on top of
sand filters, so as the backwash flows from the bottom toward the
top the dirt flows up and out while the sand stays put. So
backwashing is an effective way of cleaning a sand filter. Most
rotary valves have the steps printed right on them, and they are
- Turn off the pump. Rotate the valve to
Backwash. Roll out your backwash hose or make sure the waste
drain is open.
- Turn on the pump and watch the outgoing
water through the sight glass. it will appear clean, then dirty,
then very dirty, then it will slowly clear. When it is
reasonably clear, turn off the pump and rotate the valve to
- Turn the pump back on and run the rinse
cycle for about 30 seconds to clear any dirt from the plumbing.
Turn off the pump, rotate the valve back to Filter, and restart
the pump for normal filtration.
When the filter gauge reads 10 psi more than
when the filter is clean, it is usually time to backwash. A better
clue is when dirt is returning to the pool or when vacuuming suction
When backwashing, be sure there is enough
water in the pool to supply the volume that will end up down the
drain. It is usually a good idea to add water to the pool or spa
each time you backwash.
Sand under pressure and with the constant use
of pool chemicals or dissolving pool plaster will calcify, clump,
and become rock-like over time. Passages are created through or
around these clumps, but less and less water is actually filtering
through the sand and more is passing around it. This is called
channeling. To correct or avoid this problem, regular teardown is
- Turn off the pump. Disconnect the multiport
valve plumbing by backing off the threaded union collars. Some
valves are threaded into the body of the tank, others are bolted
on. Remove the valve.
- Some sand filters have a large basket just
inside the tank. Remove this and clean it out. The sand is now
exposed. Push a garden hose into the tank and flush the sand. As
noted previously, it will float and suspend in the water. Bust
up the clumps. As the water fills the tank, it will overflow,
flushing out dirt and debris. Be careful not to hit the laterals
on the bottom of the tank because they are fragile and break
- When the sand is completely free and
suspended in the water, not clumped, turn off the water and
replace the basket, multiport valve, and plumbing. Backwash
briefly to remove any dirt that was dislodged by this process
but not yet flushed out.
This teardown process also allows you to check
to see if the regular backwashing has flushed out too much sand. You
might need to add some fresh sand. Most sand filters need to be
filled about two-thirds with sand and have one-third freeboard.
Backwash after adding any new sand to remove dust and impurities
from the new sand.
If channeling is a problem because of hard
water or pool chemistry which speeds up calcification of the sand,
introduce aluminum sulfate (alum) through the skimmer just like you
would add DE to help prevent this problem. Use the amounts
recommended on the bag.
Every few years you need to replace the sand
completely because erosion from years of water passing over each
grain makes them round instead of faceted and rough. Smooth sand
does not catch and trap dirt as efficiently and it slowly erodes to
a smaller size than the original #20 silica, allowing it to clog
laterals and pass into the pool. Some manufacturers suggest adding a
few inches of gravel over the laterals first. This keeps the sand
separated from the laterals so the sand cannot clog them. To replace
sand, or add sand to a new installation:
- Open the filter as described previously.
Remove the old sand by scooping it out.
- Fill the bottom third of the tank with
water to cushion the impact of the sand on the laterals.
- Slowly pour the sand into the filter, being
careful of the laterals. Fill sand to about two-thirds of the
tank. Reassemble the filter parts and backwash to remove dust
and impurities from the new sand, then filter as normal.
Cleaning a cartridge filter is perhaps easiest
- Turn off the pump. Remove the retaining
band and lift the filter tank or lid from the base. Remove the
- Light debris can simply be hosed off, but
examine inside the pleats of the cartridge. Dirt and oil have a
way of accumulating between these pleats. Never acid wash a
cartridge. Acid alone can cause organic material to harden in
the web of the fabric, effectively making it impervious to
water. Soak the cartridge in a garbage can of water with
trisodium phosphate (1 cup per 5 gallons) and muriatic acid (1
cup per 5 gallons) for an hour. Remove the cartridge and scrub
it clean in fresh water. Don't use soap.
- Reassemble the filter and resume normal
Replace cartridges when they won't come clean,
when the webbing of the fabric appears shiny and closed, or when the
fabric has begun to deteriorate or tear.
Filters, do not have many repair or
maintenance problems beyond cleaning as discussed. But however, the
complaint is related to leaks of various kinds.
Backwash valves leak in two ways: internally
and externally. Internally, O-rings deteriorate and allow water and
DE or dirt to pass into areas not intended.
Piston backwash valves: The valve has
piston discs equipped with O-rings. As these wear out, water or dirt
bypasses the intended direction. Similarly, the O-rings on the
shaft, just under the handle, wear out from regular repeated use. If
you suspect the disc O-rings or see water leaking from the top of
the shaft, tear down the valve as follows:
- Turn off the pump. Remove the screws on top
of the valve cap. Pull the handle up as if you were going to
backwash, but keep pulling straight up to remove the entire
piston assembly. Replace the O-rings on each disc. They pull off
like rubber bands and the new ones go on the same way. Apply
silicone lube to the O-rings.
- Remove the handle from the piston stem. It
is held in place by setscrews or allen-head screws. This also
allows you to slide the cap off the stem. Inside the cap, you
will find two small O-rings. Pull these out with the tip of a
screwdriver and replace them. Apply silicone lube.
- Clean the stem and disc assembly and flush
out the inside of the valve body. Grit or sand can create leaks
or cause your new O-rings to wear out sooner than necessary.
Reassemble the unit the same way you took it apart.
Rotary or multiport backwash valves:
Rotary and multiport valves are similar in construction, A rotary
valve is normally mounted under a vertical grid DE filter. As with
piston-type units, these leak either externally or within the
chambers of the unit itself. If water appears under the filter, use
a flashlight to inspect underneath as carefully as possible. If you
can see or feel a leak where the plumbing enters the valve openings,
you can repair that without disassembling the entire filter. If the
leak appears to be at the joint of the valve and filter tank, or if
the problem is DE and dirt bypassing the normal flow and getting
back into the pool, you will need to tear down the filter and valve.
Another typical symptom of an internal leak is
drips coming from the backwash outlet even though the valve is
turned completely to the normal filtration position. It employs a
rotor seal that can compress or wear out. When the body gasket wears
out and water bypasses the normal flow, some leakage gets to the
backwash side and appears as a leak under the filter. If the
backwash outlet is plumbed directly into a waste or sewer drain,
this leak might not be visible.
Sometimes the problem is not in the pool or
spa itself, but in some hidden area within the system plumbing. Such
a hidden problem can also cause the system to lose prime overnight
when the pump is off. The leak drains the water from the filter
tank, then siphons the water out of the pump.
On start-up the next day, the pump has no
prime. If the pump runs dry for several hours, overheats, loosens or
melts the plumbing fittings, you will attribute the loss of prime to
the damaged plumbing. You repair the plumbing and the same problem
occurs the next day.
Have a sight glass on the backwash outflow
line so you can see any leaks and/or have a shutoff gate valve on
that line that stays closed when the valve is in the normal
To tear down this type of valve, use the
- Cut the plumbing to isolate the filter and
take the unit apart as described previously.
- Reach inside the bottom of the filter and
remove the bolts that hold the compression ring with a nut
driver. This ring holds the valve in place as well, so the valve
will now fall away from the filter tank.
- You now have the valve body with the rotor
inside. Remove the handle on the underside of the valve by
removing the bolt assembly that holds it on the rotor shaft and
slide it off the shaft. Pull the rotor out of the body. Bronze
rotors are very hard to remove and you might have to take the
valve to a pump rebuilding shop.
- Pull the old rotor seal gasket from the
rotor with needle-nose pliers. Clean the rotor and inside the
valve body. Put a new gasket on the rotor, being careful not to
over-stretch the new gasket.
- Lube the gasket with silicone lube and
replace it in the valve body. On bronze rotors, each port has an
O-ring instead of one body gasket seal as you will find on the
plastic versions. Before reassembling the filter, replace the
O-ring that sits between the tank and valve and the O-ring that
seals the shaft as it passes through the valve body to the
handle. Also replace the O-ring on the neck of the rotor. The
grid manifold sits on this neck and the O-ring seals that joint,
so to prevent dirt from bypassing the correct direction of flow,
and lube all O-rings with silicone lube.
- Reassemble the valve and tank the way you
took it apart. Be sure the tank itself is clean and that the
opening in the bottom shows no rust or cracks. If it does, you
should clean it thoroughly and have the cracks welded. Replumb
and restart the filter as described previously.
Lids and gauge assemblies
Lids on filters leak in two places: the O-ring
that seals them to the tank and/or the pressure gauge air relief
valve assembly. The lid O-ring can sometimes be removed, cleaned,
turned over (or inside out), and reused. Try the cleanup/turnover
method and if you still have leaks, then replace it.
Some filters will crack on the rim of either
the lid or the tank where the O-ring is seated. Obviously, the
problem in this case is not a bad O-ring, but a bad lid or tank.
Inspect these stress areas carefully for hairline cracks that might
be the source of the leak.
Air relief valves sometimes leak if they
become dirty or they simply wear out. Some are fitted with an
external spring that applies tension to create the seal, and when
the spring goes, so does the watertight seal. Others have a small
O-ring on the tip of the part that actually screws in to create the
seal. Unscrew this type of valve all the way. The screw part will
come out to reveal the O-ring on the tip that makes the seal, and
you can easily replace that. Air relief valves themselves simply
screw out of the T assembly. Apply PTFE tape or pipe dope to the
new one and screw it back in place.
The pressure gauge also threads into the T
assembly. If you have a leak there, unscrew the gauge, apply PTFE
tape or pipe dope to the threads and screw it back into place. If
the gauge doesn't register or seems to register low, take it out and
clean out the hole in the bottom of the gauge. Dirt or DE can clog
this small hole, preventing water from getting into the gauge.
Remember, when removing an air relief valve or
pressure gauge, you must secure the T with pliers or a wrench while
removing the component. The T assembly can easily snap off the
filter lid or come loose if you fail to hold it securely when
removing or replacing a valve or gauge.
The T assembly itself can come loose and
create a leak where the close nipple passes through the hole in the
lid. In this case you must remove the lid and tighten the nut from
the underside of the lid. Some makes of filters have a nipple welded
to the lid, so you won't have this problem unless you crack the
Dirt passing back into pool
There are many ways dirt or DE gets through
the filter and back into the pool. And the methods to make repairs.
just as a summary, check the following:
- Damaged grids, laterals, or cartridges
- Backwash valves with bad gaskets or O-rings
- Broken manifolds or retainers.
So when you feel a backwash valve getting hard
to turn, do a teardown and lubrication before the leaks occur.
Examine grids, laterals, cartridges, and manifolds carefully each
time you break down a filter for cleaning, and always take your time
when reassembling. Sloppy reassembly after cleaning is the cause of
more leaks than anything else in filters.
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