The Unfiltered Truth About Pool Filters

The Unfiltered Truth About Pool Filtration

The purpose of the filter is to remove foreign material from the water. These materials consist mainly of airborne dirt and leaves, organic matter introduced by bathers, and organisms such as bacteria and algae. Swimming pool filtration is a mechanical straining or entrapping process. A well-designed and properly operated filter will remove virtually all of the insoluble suspended matter in the water producing a sparkling clean condition. It must be recognized that a filter does not destroy living organisms such as algae and bacteria. This is accomplished by the use of chemicals.

The length of time the filter must be operated to produce the desired clarity will vary with several conditions, some of the most significant being:

1. Number of bathers
2. Temperature
3. Sunlight
4. Degree of chlorination (covered in Pool Chemistry Section)
5. Proper pH control (covered in Pool Chemistry Section)
6. Exposure to airborne contamination

There are several types of filters that may be used on swimming pools. The most satisfactory are described below:

CARTRIDGE AND ELEMENT FILTER

Cartridge filters consist of a removable-replaceable filter element. There are two basic types of cartridges, namely depth and surface. Dept cartridges consist of a thick layer of fiberous materials graded and blended to provide thousands of tiny crevices to trap dirt. Surface cartridges are made by pleating specially compounded paper or synthetic fabric to provide a large area of fiber surface in a relatively small volume. The fabric is made with controlled porosity to screen out dirt and other foreign matter as the water passes through. When the cartridge becomes clogged with dirt, it is removed, washed, and returned to the filter. Successive use of the cartridge leaves a residue of dirt so that after several cleanings the cartridge is discarded and replaced with a new one. Having a spare cartridge to alternate in use is advisable.

SAND FILTER

Sand filters are designed to operate at various flow rates depending on their tank and internal component configurations.  With correct distribution and flow of water, the carefully sized sand bed will trap dirt throughout its depth thus providing a fairly large dirt retention volume. Without correct flow distribution, dirt may be driven through the sand without performing its intended function. Cleaning of the sand bed is done by passing water at high velocity in reverse (up flow) through the sand. This causes a scrubbing action of the sand freeing the dirt, which is carried to waste.

DIATOMACEOUS EARTH FILTER

Due to the fineness of the diatomaceous earth particles, a high degree of filtration efficiency may be obtained with this type of filter. A precoat layer of diatomaceous earth (filter aid) is applied hydraulically upon the surfaces of the filter elements or other filtration surfaces. Due to the minute pores created by this precoat layer, very small particles are screened out as the water passes through the filter, thus producing a highly polished sparkling condition in the water. After the filter has removed its capacity of dirt from the water and the flow has reduced appreciably, the clogged filter aid is removed by one of several means and discarded to waste.

Surface cleaning is accomplished by automatic surface skimming and manual hand skimming.

FUNCTION OF SURFACE SKIMMER

The automatic surface skimmer is a device which is attached to the pump intake line and which rests on the pool surface. The continual flow of water from the surface of the pool through the skimmer removes floating debris such as oils, leaves, and other airborne materials before they settle to the bottom of the pool. A floating weir in the skimmer automatically adjusts for variations in the pool water level. The surface skimmer also serves as a convenient means of introducing filter aid for precoating a diatomaceous earth filter. NEVER ADD CHEMICALS THROUGH SKIMMER.

TYPES OF SURFACE SKIMMERS

1.      AUTOMATIC CIRCULAR TYPE SKIMMER – This design, attached to the suction line contains a floating weir that permits introduction of water from all directions, thus increasing the skimmer effectiveness. A self-contained strainer traps large particles such as leaves and twigs to prevent their entry into the pump.