Ord 2001-058 - Laserfiche WebLink

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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 A VB. 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 A VB 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 l2 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 DC VA . 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 accurately for only very low rates of flow (up to three gallons per minute) and must register all rates of flow. This assembly must only be used to protect against a pollutant. The DCDA is primarily used on fire sprinklersystems. (f) Pressure type vacuum breaker or PTVB. This is an assembly containing a single loaded check valve and an air opening which admits air whenever the pressure within the body of the assembly is reduced so that there is a tendency toward back siphonage. The body of the assembly must be equipped with two tight closing shutoff valves, one immediately upstream from the body and one immediately downstream of the body, and two properly located test cocks. It must be designed to operate under pressure for long periods of time without becoming inoperative, making it possible to isolate a lawn sprinkler from the potable system. It must be installed so that it is never subject to backpressure. (g) Reduced pressure backflow prevention assembly or RIP. This is a device consisting of two independently acting approved check valves together with a hydraulically operating, mechanically independent pressure differential relief valve located between the check valves and below the first check valve. These units are located between two tightly closing resilient-seated shutoff valves and are fitted with properly located resilient seated test cocks. Sec. 86.592. Types of backflow prevention required. (a) The degree of protection and the type of protection deemed necessary to prevent backflow and possible contamination of the city water system are outlined in this section. Cross connections vary widely in degree of contamination hazard. Backflow may occur under many different pressure differentials, varying from vacuum to very high pressures. The protection afforded by a backflow prevention assembly depends upon its type, the circumstances in which it is installed, and on its proper installation, testing and maintenance. C:\TEMP\backflow.doc 7