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Diatomaceous earth filters

Diatomaceous earth filters have three advantages over sand filters: They are less expensive to install, they take up less space, and they are more modest in their backwashing demands.

This type of filter strains the water through diatomaceous earth, or D.E., a sedimentary rock composed of microscopic fossil skeletons of a small water animal, the diatom. The skeletons have a highly porous lattice structure of silica which makes them almost inert to any chemical action. The D.E. rock is mined and then crushed, washed, sized, and packed as a white, flourlike powder. The coarser sizes are more adaptable to swimming pool filtration; the particular grade best suited to your equipment will be recommended by the manufacturer.

The D.E. pressure filter has practically replaced the D.E. vacuum filter. These differ in most respects, except for the filtering element itself. The vacuum unit usually operates as both filter and surface skimmer. The filter pump sucks the water through the tank and the filter leaves, which are coated with diatomaceous earth. Pool water flows over a floating weir into the filter to replace the water being drawn out by the pump. A strainer assembly in front of the filter elements catches leaves and other floating debris that would clog the filter plates.

Pressure D.E. units force the water through the filter media, much as the sand units do. Each septem (plate) has a filtering surface on both sides, and by increasing the number of plates, the filtering area is greatly increased without any appreciable enlargement of the tank. Costs range from $300 to $600.

A pressure filter does need backwashing, but only 75 gallons of water are usually required. Some pressure units are sold with separation tanks; the dirty water is backwashed through these tanks and filtered through fine-mesh bags. The cleansed water can then be returned to the pool and the dirty D.E. emptied out by hand. Such a tank often is necessary in areas where sewer connections are forbidden, since D.E. will clog a dry well and prevent dissipation of the water into the soil.

Pump and motor

The combination of pump and motor draws water from the pool, forces it through the filter, and sends it back to the pool.

The size of pump and motor is determined by the amount of water to be filtered, the rate at which it is to be filtered, and most important, the pressures at which the pump must perform. Enough horsepower should be provided to guarantee maximum filtration, but too much will damage the filter or the pump.

Horsepower alone is no gauge of the performance of a pump. The amount of water a pump will produce under specific back pressures — this is called the “pump head”— is the most important criterion of the pump’s suitability.

Most filter systems come with pump and motor included as part of the package, and most pumps are self-priming centrifugal units. A regular centrifugal pump runs the danger of losing its prime, even if a small amount of air reaches the impellor. The pump must then be stopped immediately and reprimed by hand.

A hair and lint strainer is a standard feature of all self-priming units. It catches large particles of foreign matter before they enter and clog the pump impellor.

Installing the pump requires some care. It is recommended that pumps not be located more than 2 feet above pool water level or more than 35 to 40 feet away from the pool. If the filter location must be more than 40 feet away, the pump should be installed as close to the pool as possible.

Fractional horsepower motors, from ¹/2 to 1¹/2 horsepower, require single phase, 110/220 volt circuits. Although these motors can run on either voltage, it is best to use 220-volt current to prevent overloading the circuit when starting up. In many areas, local ordinances require a special circuit for electrical motors. Even though most motors are drip- proof, care should be taken that water does not rebound into the unit from the mounting platform surface, either by rain or hosing the area.

The surface skimmer

A surface skimmer is considered standard equipment by most swimming pool builders. Dirt, oils, lotions, and floating algae tend to collect on the surface of the water, and suction from the main drain outlet at the deepest point in the pool will not pull this material down. The skimmer, which draws only surface water, is installed to remove it.

The usual surface skimmer is made of aluminum, copper, brass, precast concrete, or plastic and consists of a round tank with a projecting throat on its upper side. A self-adjusting floating weir performs the skimming action. The weir regulates the amount of water that enters the skimmer. Because it adjusts itself to allow only a thin sheet of surface water to spill over it, velocity and not volume is the key to adequate skimming.

For fiberglass and vinyl pools, special skimmers with face plates and gaskets are available. Another type of skimmer, the “lily pad,” is adaptable to in- ground pools without built-in units or can be used for above-ground pools. This unit usually attaches to the vacuum fitting and may be removed easily.

The skimmer will be most effective when it is located on the down-wind side of the pool; the wind helps the recirculating pump by pushing debris to wards the skimmer opening. If the skimmer faces away from the wind, the pump may draw in one direction while the wind blows in another, so that little water passes into the skimmer opening.

Piping the system

The plumbing system is designed to circulate all the water in the pool through the filter system. Normally, water is drawn from the pool from the main outlet and surface skimmer, passes through suction piping to the filter and heater, and then returns to the pool via pressure return lines and inlets.

The main drain is a precast concrete, plastic, or brass sump, 6 to 10 inches in diameter and 6 to 8 inches deep, set in the deepest part of the pool. It serves as a collecting point for debris and draws off dirt that settles to the bottom.

Another intake can be a vacuum line for the vacuum cleaner. But in many pools the vacuum cleaner is attached through the skimmer, eliminating the need for another vacuum line.

Suction and return lines must be of adequate size if the filter system is to operate properly. Two or three return lines are recommended, positioned to keep water moving throughout the pool.

Copper pipe (with a minimum wall thickness of Type “L”) or plastic pipe (PVC SCH 40 minimum) is almost universally recommended for private swimming pools. Galvanized steel tends to rust and has a short life when buried. For economy, however, galvanized pipe and fittings can be used near the filter, where equipment is subject to regular maintenance.

Plastic pipe has become quite popular. Its low cost, complete resistance to corrosion, good flow characteristics, flexibility, and ease of installation have made it practical for all pool piping. The semi-rigid plastics are joined with special solvent welding compounds and can be formed easily without kinking. Moreover, almost all types of fittings are available for “making up” plastic pipe and joining it to threaded connections.

Some local building codes have not yet accepted plastic pipe, and others accept it only if it carries the National Sanitation Foundation Seal; check the building codes in your area.

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