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The City of Portland, Oregon

Portland Water Bureau

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Reduced Pressure Backflow Assembly

Reduced Pressure Backflow Assembly

The Reduced Pressure Backflow Assembly (RPBA) incorporates the use of two independently-acting spring-loaded check valves separated by a spring-loaded differential pressure relief valve, two resilient seated shutoff valves and four properly located test cocks.

During normal operation the pressure between the two check valves, referred to as the zone of reduced pressure, is maintained at a lower pressure than the supply pressure.  If either check valve should leak, the relief valve is designed to open and discharge water to the outside.  A properly functioning Reduced Pressure Backflow Assembly (RPBA) will periodically discharge small amounts of water due to fluctuation in line pressure up or downstream of the assembly.  For this reason the Reduce Pressure Backflow Assembly should be installed in areas that are not subject to water damage and should be provide with adequate drainage.  During a backflow condition, the RBPA can and will discharge a large volume of water, how much is dependent upon the size of the assembly.

The Reduced Pressure Backflow Assembly is designed to prevent backflow caused by backpressure or backsiphonage and may be installed on either low or high hazard connections.

Diagrams of some typical RPBAs are illustrated below: