Installing a pool filter is a fairly straightforward process, but it always requires care and the faithful following of a few basic rules.

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 products.

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 tired 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 -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 heat resistance and compensate for a longer run.

Inspect the plumbing so you can be prepared with the proper fittings and materials when you arrive. In addition to being bothersome, extra trips to the distributor to pick up unanticipated supplies can drive your job costs way up.

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. As mentioned at the outs, the basics don't vary much from brand to brand or even type to type; nevertheless, there are distinctions with each unit that must be considered.

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 fashion.

Next, connect the circulation plumbing to the filter. 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 drrluent 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 multiport valve (some models have a push-pull valve) either by hand-tightened union connections or, if appropriate, by bonding with an adhesive, suh as a PVC cement. For threaded pipe connections, the application of Teflon tape to the threads before connecting the pipes is often recommended.

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. 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 some adhesives.

A Jump on Clean Water

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; manufacuturers' 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 filter bed.

While most sand filters use several layers of material to clean what water, some models use only one or two filtering layers. Again, watch those manufacturers specs!

Flocculents are often used to improve the performance of sand filters. Most filter "flocs" 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 3 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, 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 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 of erosion feeder that is specifically designed for precoating.

Cartridge Filters:
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. The system is now hard at work!

Manufacturer 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 dangerous.

Safety First

Although it's covered here last, 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.

According to experienced service techs, one of the key steps in avoiding such mayhem is getting the clamp assembly and O-ring seated properly on the take before pressure testing or starting the circulation system. Filter manufacturers often recommend tightening of the clamp and then taping the assembly into place around the perimeter of the tank.

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 taping 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 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!