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You are here: Home > Sprinkler School™ > Parts and Components > Backflow Devices > Reduced Pressure Zone Backflow Preventer RPZ
Reduced Pressure Principle Backflow Preventer(RPP)

Reduced Pressure Zone Backflow Preventer (RPZ)

Backflow - Parts and Components

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Reduced Pressure Zone Assembly: Inline (Underground) Installation


Because the reduced pressure zone assembly can be used on systems that distribute chemicals, underground installation requirements are particularly stringent. A drain to atmosphere is usually required and should be provided. This means a PVC drain fitting sits at the bottom of the valve enclosure and is connected to a drain line with adequate fall (slope) to drain any accumulation of water away from the valve enclosure to an area above ground with continuous gravity flow (cannot be drained into a pit with a rim higher than twelve inches below the reduced pressure zone assembly). The drainage trench should be dug in accordance with the irrigation site plan before the assembly is installed.

Typically, a reduced pressure zone assembly enclosure can be either a job-built concrete vault or two twelve-inch deep valve boxes stacked vertically with bottoms together. When using valve boxes, the lid of the bottom box is discarded. A hole at least twenty-six inches deep and three inches larger at the bottom than the dimensions of the top of a box is filled with enough drain rock to set the bottom of the lower valve box on a flat, stable surface twenty-four inches below grade. A PVC drain fitting would be glued into a 1-1/2" sanitary street quarter bend and set with the top of the drain resting on the surface of the rock. A drain line connected to the quarter bend slopes downward to above-ground atmosphere. Landscaping mesh covers the bottom of the hole before the bottom valve box is set in place.

Since an installation depth of at least twelve inches is required, the reduced pressure zone assembly is installed inline between the holes in the bottom valve box. Otherwise, the steps for connecting the reduced pressure zone assembly inline are the same as for connecting a double check valve assembly inline as explained above.

Reduced Pressure Zone Assembly: Above-Ground Installation:


Steps to install a reduced pressure zone assembly in an above-ground configuration are the same as for installing a double check valve assembly above ground, either indoors or outdoors, as explained above. When installed indoors, a drain must be provided for the relief valve. Steps to install a reduced pressure zone assembly in an "n" configuration are the same as for installing a double check valve assembly above ground outdoors except that it isn't necessary to install the two top elbows or unions as these come built into the assembly.

Reduced Pressure Zone Assembly: Maintenance


As part of the annual winterization and maintenance of the irrigation system valves, if the assembly is installed underground, clear any debris from the assembly enclosure. Open the hose bibb inside the valve box and check the end of the drain line to be sure the drain is flowing freely. Once the isolation valve has been closed and lines have been blown out, open all the valves on the reduced pressure zone assembly halfway. If the assembly is installed in an interior space, check the drain line for obstructions and ascertain that the assembly is still readily accessible.

Have the assembly tested and inspected annually in accordance with local code. Scheduling an inspection just before reactivating the system in the spring will get the season off to a good start.

Every five years, replace all non-metallic internal parts.

Reduced Pressure Zone Assembly: Repair


Each reduced pressure zone assembly comes with explicit instructions for maintenance and repair. Rubber components, check modules, and seals can be replaced by a mechanically competent homeowner or plumber. Any time the access cover is opened for any reason or the assembly is disconnected from the system, inspection and testing by a state-certified backflow assembly inspector may be required before the device is put back into service.

Replacing the entire reduced pressure zone assembly with a new one is a fairly simple process. Disconnect the assembly section at the unions, and duplicate the section using a new reduced pressure zone assembly, pipe, and fittings. Then reconnect, test for leaks, and call for inspection. If the reduced pressure zone assembly is underground, make sure underground installation is still allowed under local codes.


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