Section 3129B Rapid Sand Pressure Filters

In addition to the requirements for all filters as indicated in Section 3128B, the following apply to rapid sand pressure filters.

The filtration rate shall not exceed 3 gallons per minute per square foot (122.24 L/m per m²) of filter area. The backwash rate shall not be less than 15 gallons per minute per square foot (611.2 L/m per m²) of filter area.

The filter shall contain not less than a 20-inch (508 mm) depth of media and not less than a 10-inch (254 mm) depth of filter gravel above the underdrain system.

The filter media shall have an effective particle size between 0.40 and 0.55 millimeters and a uniformity coefficient not exceeding 1.75.

The filter gravel shall be sized and placed to provide uniform flow distribution from the underdrain system and to support the bed of filter sand without loss of sand to the pool or without development of jet streams or channeling in the filtration media.