RPZ in a Backpressure Backflow State – First and Second Check Valves Holding Tight Relief Valve Closed NOT Discharging
How does a reduced pressure principle backflow prevention device assembly protect against backflow? If the pressure downstream of the second check valve is greater than supply pressure, a backpressure condition exists. In this situation, the second check valve is designed to close tight. The inlet or supply pressure holds the relief valve closed tight. Since there is essentially no forward directional flow through the PRZ, due to the backpressure state, the RPZ device is in a static state and the first check is closed tight as well. The RPZ is providing protection, since the second check valve is preventing non-potable water for getting into the potable water. During normal operations, the downstream shut-off valve is open. If the second check valve were not holding tight the relief valve would be discharging water given that the relief valve was operating properly.
