Below is a list of terms and their explanations relating to the three types of filters (sand, diatamaceous earth, and cartridge) and the intricacies involved in the filtration process.

1- Anode- A component usually made of zinc or magnesium. It prevents electrolysis or galvanic action in steel filters.

2- Backwashing- The process of cleaning the filter and its elements by reversing the flow of water through the filter, and thereby flushing any accumulated debris out of the filter.

3- Bridging- A phenomenon in DE filters where the filter medium builds up between filter elements and limits flow.

4- Cartridge filter- A filter that uses replaceable paper or fabric-like cartridges as a means of filtration.

5- Diatomaceous Earth (DE)- A powder made of tiny plankton called diatoms. It serves as a filtration medium when it forms a cake like substance on the filter element.

6- DE filter- A filter that uses diatomaceous earth as the filtration medium.

7- Filter area- The filtering surface area through which water flows in the filter housing. It is usually measured in square feet.

8- Filter cycle- The operating time between cleaning and backwash routines.

9- Filter medium- The material used to filter debris from the water. Usually sand, a cartridge or diatomaceous earth.

10- Influent line- The plumbing line that leads from the pool to the filter equipment. It is also known as the suction line.

11- Multi-port valve- A valve that allows a multi-directional control of the flow of water through a filter. It combines the function of two or more single valves.

12- Pressure differential- The difference in pressure between the influent and effluent lines of a filter.

13- Pressure filter- The most common type of filter. The water is forced through the filter by a pump mounted on the influent side of the filter.

14- Pressure gauge- An instrument that measures the water pressure in influent and effluent lines. A prominent increase or decrease in water pressure could indicate either a need to cleaning, backwash, or a possible plugged line.

15- Sand filter- A filter that uses graded layers of sand as the filtration medium.

16- Septum- The part of the filter element or grid on which the filter medium is deposited or caked.

17- Turnover rate- The time required to circulate a volume of water equal to the capacity of a given pool.

18- Vacuum filter- 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.

19- Effluent line - The plumbing line leading from the filter equipment to the pool or spa.

Filter Types:
There are three basic types of filters: Diatomaceous Earth (DE), sand, and cartridge.

Diatomaceous 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 substance called DE, or diatomaceous earth. DE is a fine white powder found in large deposits in the ground. They act like filters by allowing water to filter through while leaving the microscopic impurities behind.

A filter must be properly sized to a pools 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 grids. A typical filter has eight grids that total anywhere from 24 to 72 square feet. The grids are placed into tanks that are 2 to 5 feet high and about 2 feet in diameter. Without the filter grids, DE would turn into a caked mass. When wet, this mass would make 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 the manifold. A holding wheel secures the grids to the manifold and a retaining rod screws into the base of the tank to secure 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.

Spin Filters

The spin filter is now obsolete, but still can occassionally be found on older pool systems. The grids are wheel shaped and lined up horizontally. They operate in a similar manner to the vertical grid filter, but in order to clean them, a crank is turned to spin the grids. Truthfully, it is not very effective and that is why it is now obsolete.

Sand Filters

Sand filters are anywhere from 2 to 4 feet in diameter. Older models generally are housed in metal tanks. The sand in the filter strains out impurities as the water pushes its way through the system. 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 of sand catch any 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.

Cartridge Filters

The operation of a cartridge filter is similar to a DE filter with the obvious exception of no DE. 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 any impurities. Unlike the backwashing method used by DE and sand filters, when it is time to clean the cartridges, they simply are removed and then washed and rinsed.

Makes and Models:

Selecting a good filtration system is the key to healthy, clean, and sparkling water. 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 the pool. To properly size and select the filter for your pool, you must first calculate the pool's volume and capacity. Next, compute the pools flow rate and the filter flow rate. Once you've done all that, you'll be ready to select the right filter for the system in question.

Sizing and Selection Techniques :

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, simply multiply the length by the width by the average depth.

For a circular pool, multiply 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 grid technique. Make a scale drawing of the pool on a piece of square-grid graph paper. Each square represents 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

To calculate the capacity, simply multiply the pool volume by 7.48. We use 7.48 because that is the number of gallons of water contained in a cubic foot of volume. As an example, suppose you have a rectangular pool that is 36 feet long and 18 feet wide, with an average depth of 5 feet. Plug these numbers into the volume equation and multiply: 36 x 18 x 5 = 3,240 cubic feet. Now plug the volume into the capacity equation and multiply: 3,240 x 7.48 = 24,235 gallons. Aren't you glad you paid attention during Math class in high school now.

Calculate The Flow Rate

The flow rate is the volume of water flowing past a given point during a specific period of time. It is 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. The turnover rate is the time required to circulate a body of water equal to the capacity of the pool.

The equation to find the flow rate for the 24,235 -gallon pool noted above (no matter what its shape) is: 24,235 / 8 = 3,029 gph. We used 8 because of an 8 hour turnover rate. To calculate the flow rate per minute, divide the flow rate per hour by 60. In this case, 3,029 @ 60 = 50.48. That is the rate at which you want the filter to work.

The calculations for your 24,235-gallon pool show that you require a flow rate of 50.48 gpm to filter the pool's capacity in eight hours. Therefore, your goal is to determine which model of filter will filter 50.48 gallons of water per minute which results in a complete turnover every eight hours in the pool.

Calculate The Filter Flow Rate

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, usually measured in square feet. The filter rate is the number of gallons of water that flows through one square foot of effective filter medium per minute during the operation of the circulation system.

A mathematics degree is not required, all you simply have to do is get both figures from the filter manufacturers. In our example, let's say you have a filter area of 4 square feet and a filter rate of 12.8 gpm. If you multiply 4 x 12.8 you have a filter flow rate of 51.2 gpm. This is relatively close to our desired flow rate of 50.48.

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 your needs.

Deciding On a Type of Filter

Do you have a preference in filters? All have their advantages and disadvantages. You probably already have a good idea of the type of filter you like, or a specific manufacturer. Once you do, you can perform the necessary calculations and select a filter that will do the job.

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 a manufacturer or dealer to ask their professional advice.

Make Sure To Oversize The Filter

When selecting a filter, keep in mind that as the filter removes debris from the water, the filter medium will become more and more clogged. This means after a while, the filter will require an ever greater flow to clean an equal amount of water. Therefore, select a filter that is larger than indicated by our calculations of flow requirements. This is especially true for commercial pools and for backwashing purposes.

Backwash Valves

This process is used to clean DE and the sand filters. The water is sent backwards through the filter, flushing any 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. They are piston and rotary (a.k.a. multiport).

Piston Valve: Water is directed to the filter in the normal operation. The water is then filtered through the DE or the sand and returned to the pool. When the handle of the piston is raised into the backwash position, the piston disks forces the water into the filter tank through the outlet port. This winds up creating the backward flow of water through the filter and flushing debris and dirt out of the tank and out of the valve inlet port. Once inside the valve again, the waste water gets directed to the waste port. Never change the piston position when operating the pump !! This creates too much pressure inside the pump and motor, which in turn can result in the valve O-rings leaking. The piston type backwash valve usually is located on the side of the filter tank.

Rotary Valve: The rotary backwash valve exclusively to vertical DE filters. The water direction is changed by rotating an internal rotor located below the filter tank. A rotor gasket seal or O-ring prevents 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. In order to backwash, you need to rotate the rotor 90 degrees. The 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 !!

Multiport Valve: The multiport backwash valve is used on sand filters and looks like a rotary valve when taken apart. Occassionally mounted on the side, but usually it is found mounted on top of the filter tank, this valve offers multiple choices 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.

Backwash Hoses

If the backwash discharge port is not plumbed directly into a drain or sewer line, a hose has to be attached to guide the dirty water to an appropriate place. A normal hose usually is 1 1/2 to 2 inches in diameter and made out of inexpensive, collapsable plastic. Backwash hoses are available in various lengths ranging upwards of 200 feet. A pool vacuum hose can be turned into a backwash hose by using a hose clamp.

Pressure Gauges and Air Relief Valves

Most filters are fitted with a pressure gauge, usually 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. A good way to know if your filter is in need of a cleaning would be if you start to see the pressure going beyond 10 pounds over the normal operating range (12-20 psi).

A pressure gauge spots potential operating problems in the system. If the pressure is lower than normal, it could indicate an obstruction in the water that is coming into the filter. When the pressure reads high, then the filter is dirty, which means either a sand change, cartridge needs to be cleaned, an acid wash is required, or there is some obstruction in the flow of water after the filter. When the pressure fluctuates while the pump is operating, the pool water level might be to low or possibly an obstruction at the skimmer. This shows just how important a pressure gauge can be.

Sight Glasses

They are the clear section of the pipe 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 monitor the effectiveness of the cleaning process. The sight glass helps to see the dirty water becoming clean and determine the appropriate time to stop backwashing.

Installation of Pool Filter

Installing a pool filter is simple, but it necessitates strict adherence to a few basic rules. Before you start getting your hands dirty, you should always consult your manufacturers' literature before working with any unfamiliar products. Here is a simple checklist of things you should consider before purchasing and/or installing a filter. 1) Where the unit is located, 2) How is it incorporated into the overall circulation system, 3) How it's tied into the pool's electrical circuitry are all very important in determining effective and efficient use of all your resources.

Equipment Pad

The equipment pad should be a level slab of poured concrete, brick, or concrete block. You should avoid installing a new filter on wood at all costs because it can warp or decay and compromise the position of the unit. Three things to remember: First, the filter should always be installed on a level surface to avoid vibration of the unit. Second, the filter should be located as close to the pool as possible. Lastly, the filter should have adequate drainage and allow for plenty of room for service access and maintenance.

Plumbing Issues

The plumbing should be designed with the premise of K.I.S.S. (keep it simple stupid). Plumbing installation should be with the shortest possible route and the least number of fittings to achieve optimum water flow efficiency. If convenience means installing away from the pool, increasing the pipe size between the filter and the pool will decrease the head resistance and compensate for a longer traveling distance. Inspect the plumbing so you can be prepared with the proper fittings and materials.

Electrical Hookup

Although the filter is not directly connected to the 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 be completed by a professional electrician in accordance with local and national electric codes.

Installation

When the equipment pad is ready, it is imperative to refer to the filter manufacturer's installation manual for specific instructions regarding installation. Once you've finished your homework, step one in the installation process is to place the filter on the pad. Make sure it is secure and level.

Next, connect the circulation plumbing to the filter. Every filter has two basic plumbing connections. They are known as 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. it would be beneficial to put a gate valve 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 then connected directly to the filters' multi-port valve. This is done by either hand-tighteneing any union connections, or by bonding with an adhesive such as a PVC cement. In the case of threaded pipe connections, the application of Teflon tape to the threads before connecting the pipes is strongly recommended.

Next, be sure the O-rings and O-ring groove on all valve fittings are clean and lubricated with a silicon lubricant. Install O-rings in their grooves and tighten with the appropriate union collar. Make sure to use the recommended primer before doping PVC components. Allow an appropriate drying period before pressure testing or operating the equipment.

Lastly, it is time to put the circulation system into full operation. Each types of filter require different start-up procedures. The following are general guidelines to use for your reference. Manufacturers' manuals will give you the specific help you need.

Sand Filters: The 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 to attain maximum 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. 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 filter bed.

Flocculents are often used to improve the performance of sand filters. Most filter flocculents are alum based preparations that forms a gelatinous layer on top of the sand. As an alternative to flocculents, diatomaceous earth can be used. As a general rule, 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 which coats the grids inside the filter tank. The DE is added as a pre-coat to the grids, and attaches itself on the grid-covering mesh. Common practice calls for adding two ounces of DE per square foot of filter area. There are variations of acceptable quantities of DE depending on manufacturer specifications.

The DE should be mixed with water and fed into the filter as a diluted or "milky" looking mixture. After turning on the circulation system, add the solution to the skimmer at a steady rate as possible to permit an even coating of the filter. DE can also be introduced to the filter by using a pre-coat pot, solution feeder, or erosion feeder that is specifically designed for pre-coating.

Cartridge Filter: Insert the filter cartridge as per its instructions and start up the circulation system. Also, you can use a flocculating agent for cartridge filters if desired. 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 always remind us to open the air release valve when starting the filter because air pressure in a filter can be very dangerous.

Safety First

Safety should always be a primary concern in filter replacement and repair. This is particularly important with units outfitted with pressure-clamp assemblies. Under certain conditions, parts can fly apart due to the tremendous force generated. In some cases, flying parts from a "blown" filter are often the source of causing property damage and/or bodily injuries. Improper application of the clamp assembly may result in a poor seal. The uneven seal might slowly force the tank out of round over time and create serious problems in any future servicing. In an extreme case, it can increase the chance of blowout of the filter. Whenever any repairs are done on a filter or related components, make sure to cut off all the pool's electrical circuits at the source!

Basic Diagnostics and Troubleshooting

A pool filter's water-cleansing function is pretty straightforward. But, small problems can become big servicing nightmares if left festering without dealing with it. When a filtration system goes a wry, the water quality can deteriorate quickly. Poor filtration leads to increased chlorine demand on the pool and can cost you a lot more money in chemicals.

The following outlines many basic filter problems, the root causes, and suggests solutions to these issues. For the most part, these discussions span across all three filter types (diatomaceous earth, sand, and cartridge). Make sure to consult your manufacturers' manuals for specific recommendations and operating guidelines.

When checking an operating filter's performance, make sure the needle of the pressure gauge 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 lead to the filter body cracking and/or failure of the clamping device on the filter tank.

Warning Sign: Reduced Flow of Water Through the Filter

As dirt accumulates on the filter media, the water flow becomes restricted and pressure within the tank begins to rise. When the pressure rises to the desired level specified by the manufacturer, it's usually time for a routine backwashing of a sand or DE filter, or a simple cleaning of cartridge filter elements.

Operating pressure ranges for filters vary widely. For example, A typical range for high-rate sand filters may be 10 to 15 pounds psi at the beginning of the filter cycle, and upwards to 25 to 30 psi when backwashing is required.

Some filter systems 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 the two readings reaches a specified level, it is time for backwashing.

Gradual pressure rises are normal during the course of a filter cycle. When the pressure begins to rise more rapidly than normal, it is time to take a close look at the elements of the filtration system.

Warning Sign : Short Cycle Between Backwashes

Short filter cycles are indicative of an excessive flow rate through the filter. Usually, it means that the filter may be undersized or that the pump may be too powerful for the system. Install a properly sized system. In some other instances, a short filter cycle indicates an unusual increase in the burden on the filter media. This can be caused by excessive dirt, debris, body oil, lotions, hair, or algae.

Warning Sign : Inadequate Filtering Action

In a sand filter, channels may have formed in the sand and gravel bed. This may be allowing water to pass through unfiltered. Look for evidence of channeling or tunneling and recharge the filter if necessary. Also, if the unit has not been backwashed consistently, mud balls may have formed on the surface of the sand bed, thereby severely limiting filtering action. In an extreme case, the sand may have calcified and will no longer filter out dirt. Look for evidence of mud balls or calcification. After backwashing if problem persists, remove the old sand and recharge the filter as necessary. Filter sand should normally last approximately four to five years.

In a DE filter, poor filtration often results from solidification of the DE. If you observe hardening of the DE, 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 feeder, the unit may not be feeding enough or to much DE into the filter. This can lead to inadequate or overcoating of the septa. Backwashing should be performed frequently enough and for adequate time periods in order for the media to be cleaned sufficiently.

It 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. To address this problem, 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 needed.

Warning Sign : Low Flow Rates in the System

Getting a low reading on a flowmeter and a high reading on the pressure gauge means something is restricting the flow. Most likely it is a blockage in the piping. In some cases, it is under sizing of the entire piping system. As a general rule, the maximum flow rate through a 1-1/2-inch PVC pipe is 70 gallons per minute. In 2-inch plumbing, it is approximately 110 gpm. A drop in the return flow could mean a clogged pump strainer basket or skimmer basket. So, make sure to clean the baskets. An ounce of prevention can save you a lot of money. If both flow and pressure readings are low, the pump may be undersized. Realistically, you may have a plugged pump impeller or lint trap. Pump or motor trouble is usually directly due to filtration problems.

Warning Sign : Sand or DE Entering the Pool

In cases when sand or DE cause a clouding water effect, check 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, the solution to this problem lies inside the tank.

With sand filters, broken laterals are a common culprit here. Replacement is the only solution.

In a DE filter, torn or worn out septa will allow DE to flow into the pool.

Warning Sign : Air Pressure Build-Up

Air present in the filter tank can compromise filtering action. In sand filters, it's a prime suspect in channeling. In DE filters, it may disrupt the filter cake. Air pressure build-up in a filter is dangerous. If can lead to hairline cracks or leaks in plumbing connections on the suction side of the pump. A low water level in the pool is another indicator of air in the system. Air may be entering through the skimmer. It is important to release any air present in the filter tank. The presence of air inhibits good filtration and can increase the danger of the filter tank suddenly cracking by rapidly increasing pressure within the tank. Air is easily released by opening the pressure release valve and allowing it to escape. When a steady stream of water comes out of the valve, you have released all of the trapped air.

D.E. Filters Troubleshooting

When working on a diatomaceous earth filter, here are some finer points to keep in mind to minimize the trials and tribulations involved in tearing down a typical D.E. unit, cleaning its grids, and recharging it in order to keep a pool's water sparkling clean.

Diatomaceous earth filters perform the same water cleaning function as sand and cartridge filters. By this I mean, they do their job with great effectiveness so long as too much dirt and debris haven't built up to clog the system. However at cleaning time, differences among these filter types become readily apparent.

A DE filter needs to be taken apart, cleaned, and recharged at least once a year. Its counterpart, the cartridge filter, only requires a simple hosing off, soaking, or routine replacement of cartridge elements. For the most part, a sand filter requires only periodic backwashing. No matter how much it helps in your overall pool-maintenance, cleaning a DE filter is a messy and unenvyable task, but a necessary evil.

To clean a DE filter, release the pressure from the filter tank. Make sure the pump is off and before taking the unit apart, 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 proceed. Then mark the lid, unscrew the clamp ring, and remove it from the tank. Mark 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 it comes time to reassemble the filter.

Remove the top of the tank and pull out the grids. Using leverage is okay, but be sure not to bend or comprimise the tank in the process. Carefully remove the tank's lid. Pull the grid assembly from the tank, making certain you don'tbreak any of the manifold fittings or cut the grid fabric on any sharp edges. 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. accordingly.
Inspect the manifold and grids. To check the manifold and grids for suspected damage, carefully remove wing nuts with a pair of pliers. Make sure not to strip the threads. Inspect the grids for any small rips or holes.

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. 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 with soap and water in cases where grease and lubricants were used. Put the band ring back and make 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 and realign it with the greased pencil marks. Put the ring clamp back on the tank and make sure it is seated properly completely around the tank.
Tighten the bolt on the clamp assembly. Use an open-end wrench if necessary, occasionally tapping the band ring to make certain it is seated properly. Follow the manufacturer's recommendation with respect to how tight a fit you need.
Recharge the D.E. Restart the pump and keep 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 until it dissolves. When the mixture is "milky" enough, pour it slowly into skimmer with the pump running. 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.

Cartridge Filter Maintenance

Servicing cartridge filters is simple. All there is to do is simply removing the cartridge elements, soaking them, hosing them off and putting them back in place. In fact, your only options with cartridge filters are either cleaning or replacement. 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.

Because thorough cleaning typically requires overnight soaking, you also need to consider what to do without the equipment in the meantime. Most people leave the system off overnight, and some replace the elements. The choice is of course, yours. As always, consult manufacturer literature for specific maintenance procedures and take care to release air pressure from the system when restarting the circulation system.

First, remove the lid. Do so 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. Next, remove the cartridges. 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.
After removing all the cartridges, you will need to rinse off the cartridges. Make sure to rinse off the cartridges by using a high-pressure nozzle. Then inspect the cartridges for any visible damage such as large tears or holes that would compromise filtration. If no visible damage exists, the cartridges should return to their original white or light gray color when properly cleaned. Then 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 for any signs of wear or at the first sign of deterioration. Clean the ring clamp and lip of the lid if necessary. Replace the lid by firmly applying manual pressure to the seat of the lid. Leaning on the lid may help, but make sure 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 Troubleshooting

A sand filter cleans a pool gradually by removing dirt, debris and particulates as water passes through a deep bed of sharp sand. 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 approximately four to five years without needing fresh sand.

The basics of sand filtration are also different from rival filter varieties. A high-rate sand filter cleans water through a process known as depth filtration. This means that dirt penetrates the sand bed and is captured in the tiny spaces between grains of sand. The depth-filtration principle works just fine unless 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.

How do you know when it's time to backwash?

One obvious clue is cloudy water. When the pool gets murky, a dirty filter is the prime suspect. Another far better clue, however, can be found with the filter's pressure gauge or gauges. If the system has both inlet and outlet pressure gauges, you will note only minor pressure differentials, a few psi, when the filter media is clean. As the sand bed begins to load up with dirt, that differential will begin to become more pronounced. 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 approximately 8-10 psi from initial post-backwash readings. It is ideal here to mark the pressure gauge with a grease pencil right after a good backwashing. Some people feel the necessity to maintain a record of the running pressure on a route sheet as you monitor filter cycles. A filter cycle can be affected by many different factors. These range from heavy bather load and algae, to wind-blown dirt and debris. Closely monitoring your pool, and efficiently backwashing, can save you money in the long run on wear and tear of your equipment.

Routing the Flow

Backwashing is a simple matter of reversing the flow through the filter by diverting the outlet water to waste.

The procedure is very easy to learn. First, turn off the pump to avoid damage to any plumbing or valves. Then, turn the control valve to the backwash position and restart the system. Once the filter has been backwashed for the desired period of time, shut the system down and reset the valves. Don't fire up the system right away as 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. Typically, a flow rate of 15-20 gpm per square foot of filter area, most manufacturers recommend to backwash for 2-3 minutes. As always, it's a good idea to cnsult manufacturer service manuals for specific backwashing procedures.

The Inner Workings of the Sand Filter

A typical sand filter in filtration mode will have a flat surface of the sand bed which indicates proper pump and filter sizing and 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 the filter. 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. There is 6-7 inches of "free space" 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. 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.

DE Filters

Backwashing a DE filter will result in some dirt and some DE being 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, you'll 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 gotten bombarded with debris due to high winds, dirt or mud, and algae. As you start to vacuum it, you'll quickly learn 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 properly.

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 encounter suction problems because the filter is clogged. Backwash, add some fresh DE, finish cleaning the pool, and then do a breakdown and clean the filter.

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 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 !!! Instead, 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.

Here is how to break down and clean a DE filter. The vertical grid tank DE filter type is explained here. This is a common in the field and if you can do these, you can do them all.

1)Turn off the pump and switch off the circuit breaker. 2) Open the tank drain and let the water run out. 3) 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. 4) Remove the retainer's wing nut and remove the retainer. Now gently remove the grids (elements). 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 or patiently excavate the dirt and DE until you can free the grids. 5)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. 6) Reach in the tank and remove the manifold from the rim of the rotary valve. 7) 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. 8) Inspect the manifold for chips or cracks. DE and dirt will go through such openings and back into your pool. Cracks can be glued. 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. 9) 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 severely 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 holding wheel. 10) 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 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. 11) 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. 12) 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. 13) 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. 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. 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, make a mixture of water and 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

Sand filters use specific size and quality of sand. 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 filters need regular backwashing. 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 very simple.

1) Turn off the pump. Rotate the valve to Backwash. Roll out your backwash hose or make sure the waste drain is open. 2) 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 Rinse. 3) 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 is poor. 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 from constant use of pool chemicals over a period of time can lead to calcification and clumping. 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 the solution.

1) 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. 2) 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 easily. 3) 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 free space. 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 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 coarse and rough. Smooth sand does not catch and trap dirt as efficiently, and it slowly erodes to a smaller size. This allows it to clog laterals and pass into the pool. 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.

Cartridge Filters

1) Turn off the pump. Remove the retaining band and lift the filter tank or lid from the base. Remove the cartridge. 2) 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. 3) Reassemble the filter and resume normal circulation.

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.

Backwash Valves

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. Tear down the valve in the following manner:

1) 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 theO-rings. 2) 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. 3) 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 filtration position.

To tear down this type of valve, use the following procedure:

1) Cut the plumbing to isolate the filter and take the unit apart. 2) 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. 3) 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. 4) 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. 5) 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. 6) 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, 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. 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 Teflon 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 Teflon 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 weld.