Ord 2011-006 - Laserfiche WebLink

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bypasses on backflow prevention assemblies must themselves include provisions for backflow prevention as described in this article. Sec. 86.591. Types of backflow prevention. (a) Air gap separation or A /G. An air gap installation separating the city water system from the customer's system is acceptable in all situations listed in this article as long as it is properly maintained. Since air gap installation separations are easily eliminated or bypassed, the director may perform field surveys and require the additional protection of a mechanical backflow prevention assembly. The air gap separation must be located as close as practical to the city water meter, and normally all piping between the meter and the receiving tank must be entirely visible. An approved air -gap separation must be at least double the diameter of the supply pipe measured vertically above the overflow rim of the vessel, but in no case less than one inch (2.54 cm). (b) Atmospheric vacuum breaker or AVB. This is a device consisting of a float check, a check seat, and an air inlet port. A shutoff valve immediately upstream may be an integral part of the device. The AVB is designed to allow air to enter the downstream water line to prevent back siphonage. This unit must never be subjected to a back pressure condition or have a downstream shutoff valve, and must not be installed where it will be in continuous operation for more than 12 hours. • (c) Check valve. Each check valve must be carefully machined to save free moving parts and assure water tightness, permitting no leakage in a direction reverse to the normal flow. The valve must be weighted or spring loaded to one pound per square inch in the direction of the flow. The face of the closure element and valve seat must be of bronze composition or other noncorrodible material which will seat tightly under all prevailing conditions of field use. Pins and bushings must be of bronze or other noncorrodible, nonsticking material, machined for easy, dependable operation. The closure element, normally referred to as a clapper, must be internally weighted or otherwise internally equipped to promote rapid and positive closure in all sizes where this feature is obtainable. (d) Double check valve assembly or DCVA. This is an assembly composed of two independently acting, approved check valves, including tightly closing resilient - seated shutoff valves located at each end of the assembly, and fitted with properly located resilient- seated test cocks. (e) Double check detector assembly or DCDA. This is a specially designed assembly composed of a line -sized approved double check valve assembly with a bypass containing a specific water meter and an approved double check valve assembly. The meter in a DCDA must register in units of gallons per minute and must register accurately for only very low rates of flow (epee less than three gallons per minute) ate. It must also register all rates of flow. This assembly must only be used to protect against a pollutant. The DCDA is primarily used on fire line spri�le systems. • 6