12 Va. Admin. Code § 5-460-210
The filtration system shall be maintained and operated as designed. In sand filters, the layer of filter sand shall be at least 20 inches in depth, properly supported by uniform layers of clean graded gravel to a minimum depth of 12 inches or supported by porous plates. The filter sand shall have an effective size of between 0.45 and 0.55 millimeters with a uniformity co-efficient not greater than 1.7. In anthracite coal filters, the anthracite shall have a depth of at least 24 inches and shall have an effective size between 0.6 and 0.8 millimeters with a uniformity co-efficient of not greater than 1.8. Pressure filters shall be equipped with readily accessible air relief valves and access holes large enough to permit inspections, maintenance, and repair work. Each pressure filter system shall be equipped with a pressure gauge at least four inches in diameter on the inlet and outlet to indicate the pressure in pounds per square inch, and a sight glass that can be easily removed for cleaning shall be provided on the waste discharge line. Gravity type filters shall be equipped with loss of head gauges.
The filtration rate for diatomaceous earth filters and similar equipment may not exceed 1-1/2 gallons per square foot of filter area with eight hours turn-over of pool volume unless continuous slurry feed is provided, in which case, the rate shall not exceed three gallons per minute per square foot of filter area.
Arrangements or equipment shall be provided for application of filter aid and proper precoating and cleaning of filter elements. All filters shall be capable of being cleaned or backwashed by use of the washwater pump and the manipulation of valves.
12 Va. Admin. Code § 5-460-210
Statutory Authority: § 35.1-11 of the Code of Virginia.