Reduced Pressure Backflow Preventers | RPZ Backflow Preventer

Reduced Pressure Backflow Preventer

A reduced pressure backflow preventer (RPZ) device is used to protect water supplies from contamination. They may also be known as reduced pressure principle backflow prevention devices, reduced pressure zone assemblies.

High hazard applications are suitable for the utilization of reduced pressure backflow preventer, that is, where the consequence of backflow into the water supply would cause significant harm. They are considered suitable because they prevent both backflow and backsiphonage, because of a redundant design (even with two check valves broken the device still provides protection), and because they are testable to verify correct operation.

RPZ Backflow Preventer

A RPZ backflow preventer often are chosen instead of an air gap since the head loss across the reduced pressure zone is much smaller.

The device consists of two independent check valves, plumbed in series, with a pressure monitored chamber between. The chamber is maintained at a pressure that is lower than the water supply pressure, but high enough to be useful downstream. The reduced pressure backflow preventer (RPZ) is guaranteed by a differential pressure relief valve, which automatically relieves excess pressure in the chamber by discharging to a drain.
Discharge from the reduced pressure backflow preventer device is an indication that either of the two check valves is ’passing’ (leaking past their shutoff seats) or the relief valve itself is faulty.

In the case of the upstream check valve passing, the differential pressure (higher supply pressure compared with the lower chamber pressure) causes any flow to occur only in one direction. A buildup of pressure in the chamber in such a case would be relieved to the drain. In the case of the downstream check valve passing, the differential backflow preventer pressure relief valve prevents the possibility of the chamber pressure from exceeding the supply pressure.

A reduced pressure backflow preventer device is tested with a device called a differential gauge. This gauge uses hoses attached to the various test cocks of the reduced pressure zone and checks to be certain that the check valve springs as well as the relief valve spring are not fouled and are working properly.

Reduced Pressure Zone : RPZ Backflow Preventers