SAND SWIMMING POOL FILTERS

Sand filters:

The sand in a 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 its clean, start-up reading, it is time to backwash the captured dirt out of the filter.

"They Say" that a sand bed should be replaced after seven years. Gradual loss of efficiency may be hard to notice. If your 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 sand deterioration, but a properly sized filter could go over 10 years between sand changes.

Use of Biguanide chemicals, i.e., Soft Swim or Baquacil require annual cleaning of the 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 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 hot. 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".

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 DE powder or other filter media.

"How do I Backwash my Sand Filter"...When the pressure gauge is reading 8-10 lbs above the clean, starting pressure (after backwashing), it is time to backwash the 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 (aka slide valve) or a multiport valve. The multiport valve has multiple ports on the valve, usually 6 positions:

FILTER: Keep it here 99%, except when backwashing, rinsing or wasting.
RINSE:   Use this setting for 20 seconds after backwashing to rinse tank.
RECIRCULATE: Use this if the filter's broken; at least you're circulating.
BACKWASH: Use this setting to reverse the flow in the filter and send water out of the waste line. Make sure valves are open or hoses rolled out.
CLOSED: Put here to close off flow from the pool, usually to work on the equipment. Do not operate pump with valve in closed position.
WASTE/DRAIN: Another filter bypass setting, but this one sends the water out of the waste pipe (hose), instead of returning it to the pool. Used to lower pool water level or to vacuum to waste.

So, to backwash a sand filter with a multiport valve;

1. Shut off pump motor
2. Press down on valve handle, rotate valve from FILTER to BACKWASH position
3. Roll out any backwash hose or open any waste line valves
4. Open air bleeder assembly on filter, and turn pump on.
5. Watch pressure gauge for backpressure and hose for kinks. Be prepared to shut off pump quickly
6. After hose fills with water, run for 2-3 minutes or until water runs clear
7. Shut off pump motor and move multiport valve handle to RINSE position Run on rinse for 15-25 seconds.
8. Shut off pump motor and move multiport valve handle to FILTER position
9. Turn pump back on and note lower pressure. Roll up backwash hose

To Backwash a sand filter with a slide valve;

1. Shut off pump motor, roll out backwash hose (if you have it)
2. Twist to unlock plunger T-handle, pull / twist plunger upwards 2-3"
3. Open air bleeder assembly on filter, and turn pump on
4. Watch pressure gauge for backpressure (+40 psi) and hose for kinks. Be prepared to shut off pump quickly
5. After hose fills with water, run for 2-3 minutes or until water runs clear
6. Shut off pump motor and push T-handle back down into locked position
7. 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, or water problems)

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.

 Sand bed replacement:    To replace filter sand, you'll first need to empty out the existing sand. One method is to spread a tarp out beneath the filter drain assembly. Then remove the entire 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.

If you have the Pac Fab Triton style dome on the top of the filter, you'll need the octagonal dome wrench to remove the filter dome. 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 Valve,  you may need to cut some pipes to remove the valve. you can reconnect them later with unions or couplings) Once these pipes are cut, the clamp band connecting the valve to the sand filter is removed, and the valve pulls straight up and off. Plug or tape or cover the standpipe so you don't spill sand in it. Then you can use a shop vac 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, not to knock or break the filter laterals at the bottom of the tank. They can be brittle when they get older, and it may be wise to replace laterals at the time you replace the filter sand. 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 multiport 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 it 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 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.

Add the recommended amount of sand only; more is not better! If you don't know this info, contact your dealer or manufacturer. Most tanks are filled only about 2/3 of the way full, to leave enough "freeboard" space on top. When full, lube o-rings and reassemble filter top. Make sure 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.

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.

Leaking 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. 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.

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. Leaks can also occur at the bulkhead unions where the valve attaches to the side of the filter, or around the threads on a top-mounted multiport. The drain plug can leak if not secured tightly or properly sealed.

Leaking valve repair. Usually a one hour job, plus internal valve components; gaskets or springs.

Filter replacement? Well, they don't last forever. But almost. A new filter may be in order if your current filter is outdated (15-20 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.