Oklahoma Administrative Code
Title 310 - Oklahoma State Department of Health
Chapter 315 - Public Bathing Place Facility Standards
Subchapter 7 - Construction and Operation
Section 310:315-7-15 - Filters

(a) General. The filter plant shall be provided with influent and effluent pressure gauges for each tank, backwash sight glass, air relief valves, and rate-of-flow indicator, as provided in this chapter. All filters must be approved and listed by the National Sanitation Foundation. In vacuum filter installations where the circulating pump has a rating of two (2) horsepower or higher, an adjustable high vacuum automatic shutoff shall be provided to prevent damage to the pump by cavitation. A compound gauge shall be installed in the pump suction line, between the pump and hair catcher (see 310:315-7-14 for exception). The sight glass may be omitted if the backwash discharge can be clearly viewed from the backwash control valves. The filter plant shall be provided with fixed piping and valving to permit the functions of filtering to pool or backwashing to approved waste disposal with the battery as a whole or any unit operated singly. The filter plant shall be provided with means for draining all filter units and piping, so that all parts of the system may be completely drained to prevent damage from freezing. Pressure tanks should be supported by jack legs or other supports to give a free movement of air under each tank and to permit access for painting. Where dissimilar metals are used in the filters which may set up galvanic electric currents, the filter plant design must resist electrolytic corrosion. The filters shall be designed in such a manner that they may be easily disassembled with allowances made for adequate working space above and around the filter to allow the removal and replacement of any part and for other maintenance.

(b) Filters, sand, conventional low-rate. This chapter shall apply where applicable to either gravity or pressure sand filters, designed for a filtration rate not to exceed three (3) gallons per square foot per minute. Filter tanks shall be designed with a factor of safety of four (4) in relation of working pressure to ultimate strength. The filter bed shall consist of suitable grades of filter sand and supporting bed of graded gravel or other porous material which shall serve to support the filter bed and distribute both filtered and backwash water uniformly. The supporting bed shall consist of graded gravel or other material and shall support not less than twenty (20) inches of filter media. The filter media shall consist of silica sand or other durable, inert material. The filter media shall be free of clay and limestone, with effective size between 0.35 and 0.65 millimeter and uniformity coefficient not exceeding 1.75. The minimum freeboard to the draw-off point of backwash water shall be not less than twelve (12) inches above the normal level the top of the filter bed. The minimum backwash rate shall be not less than twelve (12) gallons per square foot of filter bed per minute. Where anthracite coal or other filter media are employed, the freeboard shall be adequate to prevent the media being carried off to waste when the filter bed is backwashed at a rate adequate to carry off foreign material filtered from the water. The freeboard and the rate of backwash shall be the subject of individual design, based upon specific gravity of the media. The under-drain system shall be constructed of material which is corrosion resistant and enduring and the design of the system shall be such that uniform collection of the filtered water and distribution of the backwash water is effected over the entire filter bed area. Unless other effective means are provided of distributing the water entering the unit above the filtering media, the filter shall be equipped with a baffle plate for this purpose. Each conventional sand and gravel filter unit shall be provided with an access opening of not less than a standard eleven (11) x fifteen (15) inch manhole and cover.

(c) Filters, sand, pressure high-rate. High rate pressure sand filters are acceptable provided the filter-pump combination is designed and sized to limit the filtration rate to a maximum of fifteen (15) gallons per square foot per minute. The filter media shall consist of silica sand or other durable, inert material, free from clay and limestone and with an effective size between 0.40 and 0.55 millimeters and a uniformity coefficient not exceeding 1.75. The minimum depth for filter sand shall be twenty (20) inches for rapid rate filters and twelve (12) inches for high-rate filters.

(d) Filters, diatomite. These may be of either pressure or vacuum type. The design filter rate shall not exceed two and one-half (2-1/2) gallons per minute per square foot of effective filter area. If an approved body feed is not used, the rate shall be reduced to two (2) gallons per minute per square foot of effective filter area. For pools with surface area of sixteen hundred (1600) square feet or more, an approved body feed is required. The determination of the filter area shall be made on the basis of a true and effective supported septum surface. In the case of fabric septums, the area computation will be made on the basis of measurements of the septum support in a reasonably constant plane. Area allowances shall not be granted for folds in the septum fabric or deviations in the septum surface which would easily bridge. The filter cycle of the diatomite filter shall not be less than seventy-two (72) hours of continuous operation before cleaning. This shall not apply to the initial operation of a pool, but only the operation where the pool water at least meets the conditions of water quality given in OAC 310: Chapter 320. A precoat of filter aid that evenly covers the filter elements must be used before placing the equipment into initial operation and after each cleaning. The amount of filter aid shall be selected to provide at least the same protection to the filter septum as that given by 0.1 pound of diatomaceous earth filter aid per square foot of filter area where body feed is employed, or 0.15 pound per square foot where no body feed is used. The equipment shall be so arranged that during the precoating the effluent shall be refiltered or discharged to an approved waste facility without passing into the pool until the effluent is clear of suspended matter. Slurry feeders shall include an agitator and positive feed pump. Where provided, the body feeding equipment designed for feed of filter aid to the filter influent shall have a rate capacity to feed at a reasonably constant rate within a calibrated range. The equipment will have capacity to operate at the maximum feed rate of ten (10) parts per million at the design filter rate for a period of twenty-four (24) hours without refilling. The tank containing the filter elements shall be constructed of steel, plastic, or other suitable material which will satisfactorily provide resistance to corrosion, with or without coating. Pressure filters shall be designed for a working pressure equal to the shutoff head of the pump, with a factor of safety of four (4). Vacuum filters shall be designed to withstand the pressure developed by the weight of the water contained therein and closed vacuum filters shall, in addition, be designed to withstand the crushing pressure developed under a vacuum of twenty-five (25) inches of mercury, both with a safety factor of three and one-half (3-1/2). The septa or elements which support the filter aid shall be of corrosion resistant material and shall be provided with openings the minimum dimensions of which shall not be greater than 0.005 inches, or as specified in the National Sanitation Foundation Standards for Diatomite Filters. The septa shall be constructed to be adequately resistant to rupture with the maximum differential pressure between influent and effluent of not less than the maximum pressure which can be developed by the circulating pump and of adequate strength to resist any additional stresses developed by the cleaning operation.

(e) Surface skimmer filters. Skimmer filters are acceptable on pools less than sixteen hundred (1600) square feet surface area, and on wading pools. The unit shall be designed to filter at a rate of two (2) gallons per minute per square foot and shall be equal to the design capacity of the skimmer. All requirements in 310:315-7-15 are applicable to skimmer filters.

(f) Cartridge filters. Cartridge filters are acceptable if they conform to the following criteria:

(g) Filter operating instructions. At the time of final inspection of the swimming pool construction, there shall be provided to the operator two (2) sets of filter operation instructions, for the operator and owner, which refers to valve operation by number. Each valve shall be equipped with a numbered metal, plastic, or other durable tag permanently attached by a chain or otherwise permanently secured.