Reduced Pressure vs. Pressure Vacuum Breaker: Which Backflow Assembly Do You Have?

“Backflow preventer” is a family name. The brass device on your irrigation line might be a pressure vacuum breaker (PVB), a reduced pressure principle assembly (RP / RPZ), a double check (DC), or something else. Knowing which one you have helps you understand the test, the winterization steps, and why the district cares.

Pressure Vacuum Breaker (PVB)

The most common residential irrigation assembly in our area. Usually a vertical brass body with a hooded air inlet on top, installed at least 12 inches above the highest downstream outlet. Designed for backsiphonage protection on irrigation. Must be tested annually when required by your purveyor. Freeze-sensitive because it sits above grade.

Reduced Pressure Principle (RP / RPZ)

Higher hazard protection. Has two independent check valves and a differential relief valve that dumps water when something is wrong — if you have seen an assembly “spit” into a drain pan, it may be an RP. Common on commercial sites, some fire lines, and higher-hazard connections. Bulkier, often indoors or in a heated enclosure, and tested with a different procedure than a PVB.

Double Check (DC / DCVA)

Two check valves in series, no relief valve dump like an RP. Used where the hazard classification allows. Can be in-line and less conspicuous. Still a testable assembly when the water system requires it.

Spill-Resistant Vacuum Breaker (SVB) and others

SVBs are related to vacuum breaker designs with spill-resistant features for certain indoor/outdoor installs. Atmospheric vacuum breakers (AVB) appear on some hose bibbs and process equipment — not always the same “annual testable” category as a main irrigation PVB. When in doubt, match the make/model on the tag to the notice.

How to identify yours in five minutes

1. Find the brass assembly on the irrigation feed (not the plastic valve box solenoids).
2. Look for a metal tag or stamped model number (e.g. Wilkins, Watts, Febco models).
3. Note orientation: tall vertical with bonnet/hood on top → often PVB; horizontal with relief port → often RP.
4. Photo it and compare to your water district notice language.
5. Still unsure? Book a test — identifying the assembly is part of the visit.

What we test

Liberty Lake Backflow focuses on residential and light-commercial testable assemblies across Liberty Lake, Spokane, Spokane Valley, Coeur d’Alene, Post Falls, Hayden, and Rathdrum. Multi-device and uncommon assemblies are quoted before service. Standard single-device residential tests from $55.