Filter tanks shall be manufactured from fiberglass using heavy woven cloth as necessary for strength and have a minimum wall thickness of 0.3". Filter tanks are designed for 50 psi working pressure with a safety factor of 4 to 1. Tanks are factory tested at 75 psi. The underdrain system shall be such that uniform collection of filtered water and distribution of backwash water is provided under the entire bed area. The underdrain pipe is PVC with slotted orifices. The total area of slots in filter is equal to (4) times the area of inlet pipe. The orifices in top laterals are equal to (7) times the area of inlet pipe. Filter tank is provided with 12" x 16" fiberglass elliptical manway with gasketed yoke and bolt cover which is sealed by internal pressure.

Filter shall be designed for a filter rate of up to 20 GPM per square foot of filter area and a backwash rate of 15 GPM per square foot of filter area.