(A) Filters. Every pool shall be equipped with a recirculating system capable of filtering the entire contents of the pool in 18 hours or less, when the flow is calculated at a maximum of 5 gallons per minute, per square foot of filter area.
(1) Filters shall be capable of maintaining the clarity of the water to permit the ready identification, through an 8-foot depth of water, of a disc 2 inches in diameter which is divided into 4 quadrants in alternate colors of red and white.
(2) Filter capacity shall be such that it need not be cleaned more frequently than once every 4 days under normal conditions of operation.
(3) All filters shall be equipped with influent and offluent pressure gauges to determine the pressure differential and frequency of cleaning.
(4) All filter systems shall be equipped with an air release at the high point in the system. Each filter shall be provided with a visual means of determining when the filter has been restored to original cleanliness.
(5) Operating instructions shall be posted on every filter system and all valves shall be properly designated by noncorrosive tags, indicating the purpose and method of use.
(B) Sand pressure filters. Sand filter systems shall be designed and installed to operate at a rate not to exceed 5 gallons per minute, per square foot of filter area, and to backwash at a minimum of 10 gallons per minute, per square foot of surface area.
(1) Filter tanks shall be fabricated to 1956 ASME specifications for noncode pressure vessels, with the exception that standard type dished and flanged heads may be used. Tanks shall be built for a minimum of 50 pounds working pressure and tested at 150 PSI. The filter underdrain shall have an effective distribution of at least 25% of the cross-sectional area of the tank. Tanks placed underground shall be steel plate at least 3/16 inch in thickness, with an approved noncorrosive exterior coating.
(2) Filter tanks shall be supported in a manner to prevent tipping or settling.
(C) Filter media specifications.
(1) Filter sand shall be a hard, uniformly graded, silica material with effective particle sizes, between .45 and .55 milli-meters in diameter, with uniformity coefficient of 1.45 to 1.69. There shall be no limestone or clay present.
(2) Filter sand shall be not less than 19 inches in depth with a freeboard of no less than 9 inches nor more than 12 inches.
(3) There shall be no less than 4 grades of rock, which shall be clean, noncrushed, rounded, noncalcareous material.
(4) The total depth of the rock supporting bed shall be no less than 15 inches and each grade shall be 2 inches or greater in depth. Each layer of rock shall be leveled to prevent intermixing of adjacent grades.
(5) (a) The top layer shall vary in size between l/8 inch and l/4 inch.
(b) The next layer shall vary in size between l/4 inch and l/2 inch.
(c) The next layer shall vary in size between l/2 inch and 3/8 inch.
(d) The bottom layer shall vary in size between 1 inch and 1-1/2 inches.
(D) Recirculating pumps. The recirculating pump shall have sufficient capacity to provide the rated flows of the filter system, without exceeding the head loss at which the pump will deliver these flows. The pump motor shall not be operated at an overload which exceeds the service factor. The pool pump shall be equipped on the inlet side with an approved hair and lint strainer. The basket of the strainer shall be noncorrosive and have an open screen surface of at least 4 times the cross-sectional area of the inlet pipe.
(E) Pool piping. Piping shall be sized to permit the rated flows for filtering and cleaning without exceeding the maximum head at which the pump will provide these flows. In general, the water velocity in the pool piping should not exceed 10 feet per second. Where velocity exceeds ten feet per second, summary calculations should be provided to show that rated flows are possible with the pump and piping provided. The recirculating piping and fitting shall meet the following requirements:
(1) The vacuum fittings shall be located in accessible positions below the water line.
(2) A main outlet shall be placed at the deepest point in every pool for recirculating and emptying the pool.
(3) Pool recirculation piping passing through the pool structure shall be copper tubing with a minimum wall thickness of type “L” brass, galvanized iron, or A.S.A. Standards Polyethylene plastic piping.
(4) Filtered water inlets shall be provided in sufficient quantity and shall be properly spaced to provide a maximum circulation of the main body and surface of the pool water.
(F) Diatomite-type filters.
(1) Diatomite-type filters shall be designed for operation under either pressure or vacuum. The design capacity shall not exceed 3 g.p.m. per square foot of effective filter area for pressure filters and shall not exceed 2-1/4 g.p.m. per square foot of effective filter area for vacuum filters.
(2) The determination of the filter area shall be made on a 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 allowance shall not be granted for folds in the septum fabric or deviations in the septum surface which would easily bridge.
(3) 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 factory safety of 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 25 inches of mercury, both with a factory safety of 3.5. In either type filter where the tank is fabricated from material which is corroded by water, a suitable corrosion-resistant coating shall be applied to retard the attack.
(4) The filter elements shall be fabricated of corrosion-resistant materials throughout. They shall be designed to be adequately resistant to a differential pressure between the influent and the effluent of not less than the maximum pressure which can be developed by the circulating pump, and shall be of adequate strength to resist any additional stresses developed during the cleaning operation. The filter septum, on which the filter-aid cake is deposited, shall be provided with openings the maximum dimensions of which shall be not greater than .005 inches.
(5) (a) Provision shall be made to introduce filter aid into the filter in such a way as to evenly precoat the filter septum before the filter is placed in operation.
(b) The amount of filter aid shall be selected to provide at least the same protection to the filter septum as would be provided by the use of l/10 pound of diatomite filter aid per square foot of filter area.
(c) Use of additional equipment to provide body feed to the filter influent is optional.
(d) Where provided, this equipment shall have the capacity to continuously and uniformly feed at a rate of not less than l/10 pound of filter aid per square foot of filter area per 24 hours.
(6) (a) The filter piping shall be so designed that during the precoating operation the effluent from the filter shall be recirculated or run to waste and shall not be fed into the pool until free of filter aid.
(b) An exception to this requirement may be made if the filter septum is of the construction that no perceptible quantity of filter aid is introduced into the pool when the effluent discharges therein.
(7) Where dissimilar metals are used in the construction of the filter, which may set up galvanic currents, suitable provision shall be made to resist electrolytic corrosion.
(8) Filters shall be so designed and installed that they can readily be disassembled and the filter elements removed.
(1979 Code, § 158.21) (Ord. 1531, passed 6-13-1953; Am. Ord. 1818, passed 4-20-1960) Penalty, see § 158.99