Sand filter systems shall be designed and installed to operate at a rate not to exceed five gallons per minute per square foot of filter area, and to backwash at a minimum rate of ten gallons per minute per square foot of surface area.
(a) Filter tanks shall be fabricated to 1956 American Society of Mechanical Engineers 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 fifty pounds working pressure and tested at 150 psi. The filter underdrain shall have an effective distribution of at least twenty-five percent of the cross-sectional area of the tank. Tanks placed underground shall be steel plate at least three-sixteenths inch in thickness, with an approved noncorrosive exterior coating.
(b) Filter tanks shall be supported in a manner to prevent tipping or settling.
(Ord. B-751. Passed 7-9-62.)