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. We’ll cover all that and more in this basic filter installation guide.

Safety first

Safety must be a primary consideration every step of the way. It is particularly crucial for units outfitted with pressure-clamp assemblies, which can fly apart with tremendous force under certain conditions. In fact, flying parts from a “blown” filter often are the source of property damage and the cause of severe, sometimes fatal, injuries.

Clamp assembly: One of the best ways to avoid such mayhem, experts say, is to get the clamp assembly and O-ring seated properly on the tank before pressure testing or starting the circulation system. Filter makers often recommend tightening the clamp to specifications using a torque wrench.

Extra care in placing the assembly around the tank and tightening it is critical. Some manufacturers recommend partially tightening the clamp and then, with a rubber mallet or hammer handle, tapping the assembly into place around the perimeter of the tank.

Improper application of the clamp assembly may result in a poor seal that could cause the filter to separate. Alternatively, the uneven seal might slowly force some tanks out of round over time and create serious problems in future servicing — and further increase the chance of blowout. (Safety tip: Always stand away from the filter while it is filling.) Most filters now have a spring assembly, which aids techs in knowing when the clamp is properly tightened. Open the air bleed valve and let the air out after the pump is turned on to test that the filter is assembled properly. When water emerges from the bleed valve, close the valve.

Electricity: Whenever any repairs are done on a filter or related components, shut off all the pool’s electrical circuits at the source. And, if necessary, pull the circuit breakers.


Next, it’s time to get down to the hands-on part of filter installation.

Equipment pad: There are several ways to go here. Prefabricated slabs are popular in some quarters nowadays. But if you go the traditional route, be sure the equipment pad is 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: (1) Filters should always be installed on a level surface; if things aren’t square, the unit may vibrate or not operate at its optimum. (2) Filters should be located as close to the pool as possible. (3) The filter should have adequate drainage and, in the best of all worlds, 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 when you arrive. Extra trips to the distributor to pick up unanticipated supplies can drive your job costs way up.

Electrical hookup: Although the filter is not directly connected to electrical power, the pump motor runs on electricity, which means the filter must be grounded, if metal. Also, the electrical wiring and hookup of the motor must have been completed by a licensed professional in accordance with local and national electric codes.


Now that the pad is ready for the new filter, it’s particularly important to refer to the filter manufacturer’s installation manual for instruction regarding the specific make and model of the filter you’re installing.

Filter placement: Once you’ve read the manufacturer’s manual, place the filter on the pad. Consider bolting the unit to the pad, although it’s not necessary.

Filter connection: Connect the filter to the plumbing. Every filter has two basic plumbing connections: the influent and 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 of the filter if it is located below the surface of the pool. Some techs opt for a ball valve or diverter valve instead. Standard practice calls for installing a flap check valve (a union flap check valve is preferred) between the pump and filter on all pools with equipment positioned above the pool water. This will permit you to close the lines when it’s necessary to service, remove or replace the filter.

The plumbing lines are connected directly to the filter’s multiport valve (some models have a push-pull valve) either by hand-tightened union connections or, if appropriate, by bonding with an adhesive such as a PVC cement. It is recommended that Teflon tape or other types of approved sealants be applied to the threads before connecting the pipes.

Be sure the O-rings on all valve fittings are clean, and that each O-ring and O-ring groove is lubricated with silicone lubricant or a nonaggressive/nonpetroleum-based 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. Use the recommended primer before applying PVC pipe joint cement.

Allow an appropriate drying period before pressure testing or operating the equipment. Take into account the fact that temperature and humidity may affect the drying time of some adhesives.


Once the filter is installed on the pad, all of the plumbing connections are set and the unit is properly grounded, it’s time to put the circulation system into full operation. The three main types of filters require different start-up procedures. The following are general guidelines; manufacturers’ manuals will give you the specific help you need.

Sand filters: Most sand filters in use today are high-rate models that use No. 20 silica sand. In other models, water typically passes through a number of layers of sand and gravel that have been carefully placed in the tank. Check the specs provided by the filter maker before adding any materials.

The size of the sand particles used as the filter medium is key for optimum efficiency. If the sand granules are too big, filtering efficiency is decreased. Conversely, if the sand particles are too small, the filter will clog up quickly and the sand may pass through the laterals, ending up in the pool.

If you do use the layering method, 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 filter bed.

Flocculants often are used to improve the performance of sand filters. Most filter “flocs” are alum-based and form a gelatinous layer on the top of the sand. As an alternative, diatomaceous earth can be used: Add ½ cup of DE for each 3 square feet of filter area after the unit has been filled with sand. Experts note that the DE could wind up back in the pool, so it’s best not to add it after backwashing.

DE filters: These units filter the water by passing it through a layer of diatomaceous earth, which 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 2 ounces of DE per square foot of filter area, with a typical variation of a ½ cup either way, depending on the unit’s specs.

The DE often is 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 a rate as steady as possible to permit even coating of the septa. Ideally, the DE will form a uniform “cake” between 1⁄16- and

1⁄8-inch thick.

DE also can be introduced to the filter by using either a precoat pot, a solution feeder or an erosion feeder that is specifically designed for precoating.

Cartridge filters: Setup of cartridge filters is simple. Just insert the filter cartridge per instructions and turn on the circulation system. You can use a flocculating agent for these filters — however, it may require more frequent cleaning of the cartridges.


The final step in this process — regardless of filter type — is to open the filtration unit’s air release valve and turn on the pump. When a steady stream of water shoots out, close the valve. The system is now working.

Be advised that, in many cases, this step has been rendered unnecessary. Most modern filters have an automatic air relief built into them to prevent any damage on start-up. If that’s the kind of unit you’re working with, your job is even easier.

A final note: If you’re starting up a filter on a new or replastered pool, be sure that the plaster dust is removed or it can cause damage to the elements.