Short definition
A pressure-vacuum breaker (PVB) is a backflow assembly designed for continuous-pressure systems — primarily irrigation. It has a spring-loaded check valve and an air-inlet valve above the check that opens when supply pressure drops, admitting air to break a siphon. Listed under ASSE 1020. The dominant residential irrigation backflow assembly in Washington, required by WA DOH cross-connection rules.
What it is
The PVB body contains a single spring-loaded check valve plus an air-inlet (atmospheric) valve mounted above it. Two test cocks (small ports) allow a certified BAT to verify the device during the annual test. Two shutoff valves (one upstream, one downstream) allow isolation for testing and service.
A critical install rule: the PVB must be installed at least 12 inches above the highest downstream outlet — meaning above the highest sprinkler head on the system. The minimum elevation ensures the air-inlet vent functions properly when supply pressure inverts.
The PVB protects against back-siphonage only — not back-pressure. If the irrigation system has any pressurized chemical-injection or fertilizer-injection equipment, a PVB is no longer sufficient and the application requires an RPZ instead.
Why it matters to a homeowner
If you have an in-ground sprinkler system in WA, you almost certainly have a PVB. It’s the green bonnet sticking up out of the ground next to the irrigation manifold or up against the foundation, with shutoffs and test cocks visible. It’s required by code, it’s tested annually by a certified BAT, and it freezes if not winterized.
Practical homeowner experience:
- New irrigation install includes a PVB at the supply tee, mounted 12+ inches above the highest sprinkler head, with the initial test before utility activation.
- Annual test letter from utility — schedule a BAT, $50–$150 typical.
- Mid-winter freeze burst. PVBs commonly fail when un-winterized irrigation lines freeze and crack the assembly. Replacement runs $300–$700 for the assembly plus labor. Going forward, fall winterization (close the supply, blow out the lines with compressed air) prevents recurrence.
- Inspection identifies a PVB installed too low — under 12 inches above the highest head — and requires it to be raised on a riser.
When you’ll encounter this term
- New irrigation install requires a PVB and an initial certified test.
- Annual test letter from your water utility.
- Winter freeze cracks the PVB; spring-startup leak triggers replacement.
- Inspector flags a PVB installed below the 12-inch elevation requirement.
- Homeowner adds chemical injection to irrigation — must upgrade to an RPZ.
Common variants and what it isn’t
- PVB vs. SVB (spill-resistant vacuum breaker, ASSE 1056). SVB is similar but with reduced spillage at startup. Sometimes preferred where the standard PVB’s startup spill is a nuisance (water dribbles out of the air-inlet vent at each system startup).
- PVB vs. DCVA. PVB is back-siphonage only; DCVA is back-pressure plus back-siphonage. Some WA utilities prefer DCVA over PVB on residential irrigation; others prefer PVB. Confirm locally.
- PVB vs. RPZ. RPZ is high-hazard with both back-pressure and back-siphonage protection. PVB is low-hazard, back-siphonage only.
Common failure modes
- Air-inlet valve sticking — won’t admit air during a back-siphonage event; assembly fails the annual test.
- Spring fatigue on the check valve — slow reverse leak.
- Freeze damage in unprotected exterior install. The single most common WA PVB failure.
- Mineral deposits at the check seat — partial close, fails annual test.
Washington note
WA DOH WAC 246-290-490 recognizes PVB for back-siphonage protection on continuous-pressure low-hazard cross-connections. Annual testing by a certified BAT is required; results submitted to the water utility. Some WA jurisdictions prefer DCVA on residential irrigation rather than PVB — local utility ordinance or program manual sets the choice.
WA winterization is non-negotiable for outdoor PVBs. The standard fall protocol: shut off the irrigation supply at the indoor stop-and-waste valve, then blow compressed air through the manifold and zone lines from the system controller side to clear standing water from the PVB body and downstream lines. Skipping winterization in WA’s freeze-prone areas means buying a new PVB in spring.