Reduced Pressure Principle Backflow Prevention Device Assembly

The reduced pressure principle backflow prevention device assembly (RP) also known as a reduced pressure “zone” backflow prevention device assembly (RPZ) is a mechanical backflow prevention method that provides protection against backsiphonage and backpressure. It is known as a RP or RPZ, since the pressure in the zone between the two check valves is reduced. (In this document it will be referred to as an RPZ) The RPZ consists of two internally spring loaded check valves in series operating independently and an internally spring loaded relief valve with atmospheric vent located between the two check valves. This area is known as the “zone.” The spring loading provides the ability to bite through small debris and still seal, a protection feature not prevalent in unloaded swing check valves. The RPZ shall comply with the American Society of Sanitary Engineering 1013 Standard.

The RPZ is fundamentally an actuating air gap with check valves on all sides, thus it is very effective in preventing a cross-connection incident, if the relief valve is operating properly. The relief valve is hydraulically dependent on the first check valve differential pressure. A design characteristic of the RPZ is that water may intermittently or constantly discharge from the relief valve during normal operations. Because of this design characteristic, installing an RPZ on a service line or fire protection can be problematic. Discharge from the relief valve will occur and drainage requirements need to be considered when installing a RPZ.

The RPZ can be tested in-line to evaluate the operation of the check valves to close drip tight and for the relief valve to open. The RPZ can also be repaired in-line (in-line means not having to physically remove the device). The RPZ should be tested at least annually by a certified tester; however, this backflow preventer is unique in that it will visually indicate check value failures. A constant discharge of water from the relief valve is an indication that the first or second check valve depending on the hydraulic situation is not closing properly. The RPZ can be used for direct cross-connections to prevent backsiphonage and backpressure. The RPZ may be subjected to continuous or intermittent pressure conditions. The maximum working pressure is 175 PSI and operating temperature is 33 degrees to 180 degrees Fahrenheit.

The RPZ are used for high hazardous situations such as but not limited to fire system utilizing chemicals, fire hydrant used during construction projects and mortuaries.

The RPZ shall never be installed in a pit or area subject to flooding, since the air gap will be compromised.

The RPZ comes in a variety of sizes and shapes but they all function in the same manner. Size or shape does not have any relationship on the testing technique. The sizes range from ¼ inch to 12 inches.