Reduced Pressure Principle Backflow Prevention Device Assemblies Installed on Fire Protection Systems – Reduced Pressure Principle Detector Assemblies

Reduced Pressure Principle Detector Assemblies (RPDA) may be installed on fire protection systems to provide maximum protection against backflow and at the same time detect leakage or unauthorized use of fire sprinkler water. The RPDA is a reduced pressure principle backflow prevention device assembly with a bypass arrangement attached to the main assembly upstream of the first check valve and downstream of the second check valve. The bypass includes a water meter and a reduced pressure principle assembly. The reduced pressure principle assembly installed on the bypass is designed to require all flows of 2 GPM or less to pass through the bypass and be recorded on the water meter. The design specifications for a RPDA are that the first check valve in the main assembly shall have a greater resistance than the first check valve in the bypass assembly. With this configuration, low flows of water will pass through the bypass as opposed to passing through the main assembly. The pressure loss through a RPDA main body is greater than the pressure loss through a RPZ. The RPZ on an average will reduce the pressure by 8 to 10 PSI.

There are two types, the Reduced Pressure Principle Detector Assemblies and Reduced Pressure Principle Detector Assemblies Type II. The Type II is similar to the RPDA except that the bypass arrangement is different. In the TYPE II, the bypass arrangement is attached to the main body of the assembly downstream of the first check valve and relief valve, and downstream of the second check valve. The bypass included a water meter and a single spring loaded check valve. The Type II bypass uses the first check of the main assembly as the first check valve of the bypass.