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Pool Filters

Example of a Sand FilterSAND POOL FILTERS


The sand in a pool sand filter (#20 silica sand; 45 - 55 mm) is specially graded to trap particles in the 20 - 100 micron range. As a sand filter collects dirt, its efficiency increases, trapping more dirt. When your pressure gauge shows a reading 8 - 10 lbs. over the clean, start-up reading, it is time to backwash the captured dirt out of the filter.


Sand filters are known to be the lowest maintenance of the three types of pool filters. You may only need to open up the tank every 5 years or so. DE filters require removing the internal grid assembly at least annually to clean them well, and cartridge filters don't backwash, you remove the cartridge and hose clean every so often, depending on the cartridge filter size. Sand filters are the easiest to operate and maintain.


"They say" that the sand inside a sand filter should be replaced after seven years. Gradual loss of efficiency may be hard to notice. If your sand filter requires frequent backwashing, every week or two, the sand bed may be "mudballed", or it may be "channeled". It may also "calcify" with calcium deposits. Other water balance problems may also contribute to pool filter sand deterioration, but a properly sized sand filter could go over 10 years between sand changes.


Use of Biguanide chemicals, i.e., Soft Swim or Baquacil require annual cleaning of the filter sand to prevent it from "gumming-up". High amounts of bather oils can gum-up a sand bed. And just the years of a pump forcing water over the grains wears away the sharp edges of the sand. Such pool filter sand becomes more circular, and traps dirt less efficiently.


Remember that for sparkling water, we need the trio of sanitation, filtration and circulation. If one of these areas is lacking, the water won't look so good. So, if you've kept very good chemical maintenance and your circulation is good, you may have a filter problem. Is the filter sized properly? Many filters of the 70's - 80's were grossly undersized, the trend now in pool filtration is "Go Big Early." In ground pools should have a 3.1 sq ft sand filter or greater.


Adding a small amount of aluminum sulfate or "alum", through the skimmer will form a gelatinous layer on top of the sand bed, useful in cleaning up an undesirable water condition. You can also add a small amount of D.E. powder or other filter media.


"How and When do I Backwash my Sand Filter?"


When the pressure gauge on your sand filter is reading 8 - 10 lbs above the clean, starting pressure (after backwashing), it is time to backwash your sand filter. This process involves turning a valve so that the water will flow through the filter backwards, flushing out the dirt - Hence the name "back-washing." Sand filters can have either a push-pull valve (also known as a slide valve) or a multiport valve. The multiport valve has multi-ports on the valve, usually 6 positions. Always shut off the filter pump before turning the filter valve.

  1. FILTER: Keep it here all the time, except when backwashing, rinsing or wasting

  2. RINSE:   Use this setting for 15 seconds after backwashing to rinse the sand filter tank

  3. RECIRCULATE: Use this if your filter's broken; at least you're circulating the water

  4. BACKWASH: Use this setting to reverse the flow in the filter and send water out of the waste line. Make sure valves are open and your backwash hose is rolled out

  5. CLOSED: Put here to close off flow from the pool, usually to work on the equipment. Do not operate pump with valve in the closed position

  6. WASTE/DRAIN: Another filter bypass setting, but this setting sends the water out of the waste pipe (hose), instead of returning it to the pool. This setting is used to lower pool water level or to vacuum to waste.

So, to backwash a sand filter with a multiport valve;
  • Shut off the pump motor

  • Press down on valve handle, rotate valve from FILTER to BACKWASH position

  • Roll out any backwash hose or open any waste line valves

  • Open air bleeder assembly on top of sand filter, and turn pump on.

  • Watch pressure gauge for backpressure and hose for kinks. Be prepared to shut off pump quickly if the pressure gauge spikes or if the hose kinks up.

  • Let the pump run for 2 - 3 minutes on BACKWASH or until water runs clear
  • Shut off pump motor and move multiport valve handle to RINSE position Run on rinse for 15 seconds.

  • Shut off pump motor and move multiport valve handle to FILTER position

  • Turn pump back on and note lower pressure. Roll up backwash hose

To Backwash a sand filter with a slide valve (push-pull valve);
  • Shut off pump motor, roll out backwash hose (if you have it)

  • Twist to unlock plunger T-handle, pull / twist plunger upwards 2 - 3" (PacFab valves are reverse)

  • Open air bleeder assembly on filter, and turn pump on

  • Watch pressure gauge for backpressure (+ 30 PSI) and hose for kinks. Be prepared to shut off pump quickly

  • After hose fills with water, backwash your sand filter for 2 - 3 minutes or until water runs clear

  • Shut off pump motor and push T-handle back down into locked position

  • Turn pump back on and note lower pressure. Roll up backwash hose

A properly sized sand filter should, in most cases, be able to operate continuously for a period of 4 weeks between backwashings. A "Filter Run" of less than 4 weeks may indicate sand problems (or sizing problems). It's a good idea to mark the pressure gauge with "Clean" & "Dirty" marks, or write the numbers on the tank, i.e., 8/16 to serve as a reminder when you need to backwash your sand filter.


Filter Sand in the pool?


Bad news. If it hasn't blown in, or been carried in on the feet of swimmers, it's likely coming from the filter. A broken lateral or standpipe may be the cause. You'll need to empty the tank, locate and make the repair, refill with fresh sand and test. If you have overfilled your sand filter, it is not uncommon to experience a small amount of "blow back" after backwashing. Continued sand leakage during filtration usually indicates a lateral breakage. Don't confuse brown dust as sand particles.


In fact, it's common to experience a small amount of dust blown back into the pool after backwashing a sand filter, even with rinsing first. If you see deposits of a dusty, sand colored material on the pool floor, hit it with you pool brush, if it becomes waterborne as a "poof" of dust, then sand it is not. If you have a problem with fine dust constantly passing through your sand filter, you can vacuum this out to waste after filling the pool first. If this problem continues, you may have sand bed problems, or a sand filter that is too small for the pump.


Filter Sand bed replacement:


To replace your filter sand, you'll first need to empty out the existing sand in the tank. One method is to spread a tarp out beneath the filter drain assembly. Then remove the entire filter drain assembly, turn on the pump, and step back! The water pumping through the filter will remove most of the sand out the drain hole. Another method is to remove the drain plug only and allow the filter to drain for several hours or days. Then, remove the top dome or multiport valve from the top of the filter.


If you have the Triton style dome on the top of the filter, with a side mounted filter valve, you'll need the octagonal dome wrench to remove the dome. If you don't have a dome wrench, you can use a large strap wrench or in a pinch, a screwdriver and hammer. Once the dome is removed, gently twist the baffle/pipe out of the way so you can get a scoop to the sand.


If you have a Top Mount Multiport,  you may need to cut some pipes to remove the valve. You can reconnect them later with pvc unions or couplings and some pvc glue. Once these pipes are cut, the clamp band connecting the valve to the filter is removed, or in the case of older sand filters, several bolts are removed, and the valve pulls straight up and off. You may need to use a little effort with prying and twisting to release the valve off of the standpipe and flange. Plug or tape or cover the standpipe so you don't spill sand in it. Then you can use a shop vacuum to suck out the sand, or you can use a small cup to scoop out the sand. 


Be very careful as you scoop or suck the sand out, not to knock or break the laterals at the bottom of the tank. They can be brittle when the get older, and it may be wise to replace laterals at the time you replace the filter sand. Once all of the sand is scooped out, use a hose to wash out the sand beneath the laterals. When the tank is empty of sand, replace the drain assembly, using silicone sealant on the threads. Then add enough water to cover the laterals, so the new sand pouring in won't crack them. Again, if you have the top mounted multiport, cover the standpipe opening. If you have a side mounted filter valve, gently push the intake baffle to one side, or wrap the baffle with a small plastic bag to keep the sand from entering the pipe as you pour it in.


Pour the new filter sand in! Use only specially graded pool filter sand; #20 silica sand, 45 - 55 mm. On top mounted multiport filters, use care to keep the lateral/ hub assembly positioned in the center, and on the bottom of the tank. After each bag of sand is added, make sure it is still centered. It may be useful to have a helper hold the standpipe in place while the sand is added.


The best method is to lift the sand bag up onto the tank, and use a razor knife to cut from the bottom-belly of the bag. Keep care not to breathe in the silica dust while pouring, and on older fiberglass sand filter tanks, wear long sleeves to keep from getting "fiber-rash".


Add the recommended amount of sand only; more is not better! If you don't know this info, contact your dealer or manufacturer. We have the information on most of the sand filters we sell. Most tanks are filled only about 2/3 of the way full, to leave enough "freeboard" space on top. When full, clean and lube o-rings and reassemble filter top, making sure to use a brush to remove small sand grains. Make sure filter lid is very secure, lids that blow off can be very dangerous. It's a good idea to replace the o-ring on the filter domes, if it is distended or dry-rotted.


When the filter is started up, start up on "RINSE" setting first (if you have a multiport valve). Then backwash and rinse again. If you have a push-pull valve, backwash first. This final step will prevent putting a lot of "sand dust" into the pool after a sand change. Note your new pressure, it usually will be less than before the sand change.


Leaking sand filter?


Sand filter tanks rarely leak themselves, however leaks often occur in and around the multiport interface. A common complaint is that water is leaking out of the backwash port of the multiport (six position) valve. If your sand filter tank is leaking, or has small cracks in it, replace it immediately. There is no safe, effective means to patch a sand filter tank.


Sand filters can leak from the drain assembly. Try to determine if the leak is from the assembly that is screwed into the body of the tank, or if it is the cap or plug that is leaking. Some sand filter drain plugs have small o-rings or gaskets that need periodic replacement.

You may have a push-pull valve, or slide valve as it is sometimes called, instead of a multiport valve.  Leaks can occur through the top of the index plate, or out of the backwash line. This is a easy inspection to determine what o-rings need to be replaced on the plunger.

Leaks can also occur at the bulkhead unions where the valve attaches to the side of the filter. The bulkhead assembly itself may have loosened. This repair is usually more complicated, as you may need to access the bulkhead from both sides of the filter tank.

Leaking Multiport valve repair:


Is water leaking out of the backwash port of the multiport valve? Slight adjustments of the handle may temporarily solve this problem. A more permanent repair may necessitate replacement of the spider gasket inside of the multiport. You may also have leakage up around the middle of the handle on the valve, which external adjustments rarely fix. This usually requires replacement of a Teflon washer and sometimes the spring as well.


Filter replacement?


Well, they don't last forever. But almost. A new filter may be in order if your current filter is outdated (20-25 yrs old) and difficult to use or get parts for. If the filter tank has cracked, usually from freeze damage or possibly from closing off return valves while the pump is running, a new filter is in order. Replacement is usually fairly simple, with just a few plumbing fittings needed.


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Compare and Shop for Swimming Pool Filters

Parts and Accessories for Swimming Pool Filters

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