Reduced Pressure Principle Backflow Prevention Device Assembly Relief Valve Discharge Intermittently

Water will intermittently discharge from the relief valve due to inlet water pressure fluctuations (decrease in inlet pressure). The relief valve spring will keeps the pressure downstream of check valve number one at last 2.0 pounds per square inch less than supply or inlet pressure. The relief valve senses the hydraulic conditions upstream and downstream of the first check valve and will make adjustments to maintain a water pressure downstream of the first check valve lower than the upstream pressure. A RPZ that is installed on a service line where the relief valve discharges and stops repeatedly is most likely correcting for water supply pressure fluctuations.

Water will continually discharge from the relief valve when the first check vale is fouled (will not close) and the RPZ is in static or no flow state or the second check valve is fouled (will not close) and the backflow prevention device is in a backpressure state. With this design criterion, the RPZ will provide protection against backsiphonage and backpressure when both the first and/or second checks are fouled, as long as the relief is functioning properly. The down side of this situation is that water is discharging from the relief valve when there is no demand downstream or when backpressure is occurring and the first or second check valves are fouled.

Because of the inherent design of a RPZ, fluctuating supply pressure on an extremely low flow or static flow condition may cause nuisance dripping and potential fouling of the assembly. While not effective in all cases, the installation of a soft-seated check valve immediately ahead of the RPZ will often hold the pressure constant to the assembly in times of fluctuating supply pressure.