Pressure vacuum breaker (PVB) testing
Pressure vacuum breaker. Moderate-hazard protection. Tested annually under Durham Region By-law 24-2018.
What a pressure vacuum breaker is
A pressure vacuum breaker (PVB) is a compact backflow preventer with one spring-loaded check valve and, above it, a spring-loaded air inlet valve under a canopy. Under normal supply pressure the check is open and the air inlet is held shut. If supply pressure drops (a main break, hydrant flushing, heavy demand), the check closes and the air inlet pops open, letting air into the pipe so a vacuum cannot pull water backward from the irrigation lines into the building or the municipal supply.
That protects against backsiphonage only. A PVB has no defence against backpressure, which is why it must be installed above the highest downstream outlet (usually 300 mm above the highest sprinkler head) and why it cannot be used where a pump or elevated piping could push water back toward it.
Where PVBs are used in Durham Region
Almost always on irrigation. Commercial plazas, condo and apartment grounds, school fields, church lawns, cemetery and municipal-style landscape systems, and industrial sites with turf. Some outdoor hose and wash-down connections use one as well.
| Situation | Right device |
|---|---|
| Irrigation, no chemical injection, PVB can be mounted above all heads | PVB |
| Irrigation with fertiliser or chemical injection | RPZ |
| Irrigation where the device would sit lower than some heads | RPZ, or a DCVA where the hazard is moderate and backpressure is possible |
| Irrigation fed by a well or pond on the same site | RPZ on the municipal service (auxiliary supply) |
Under By-law 24-2018 every backflow preventer on an industrial, commercial, institutional or multi-residential property is tested annually, and irrigation devices are not exempt. They just tend to be forgotten because they sit outside and are only pressurised half the year.
Timing: spring start-up is the test window
Irrigation devices are winterised in the fall (water drained, system blown out) and can only be tested when the system is pressurised. That makes spring start-up the natural moment: the irrigation contractor turns the system on, and the backflow test happens the same week. Doing it then catches freeze cracks and stuck air inlets before the first watering, and gets the report to BSI Online early in the season.
If the due date on your Region notice does not line up with your start-up date, say so when you book. The test has to happen when the device is live, so it may make sense to pressurise that zone early for the test.
What the annual PVB test checks
With a calibrated differential pressure gauge on the two test cocks, the tester confirms:
- Air inlet valve. As pressure is bled down, the air inlet opens fully at or above the minimum differential in CSA B64.10.1.
- Check valve. Holds tight against reverse flow and maintains the minimum differential.
- Shut-off valves. Both close and hold, so the device can be isolated for the readings.
- Test cocks. Free, not leaking.
Report filed through BSI Online, reviewed by the Region, tag issued. $25 BSI filing fee per report, subject to annual increases.
Why PVBs fail
- Stuck air inlet. The device sat idle all winter. Debris, insects, or a dried seal keep the poppet from lifting. The most common PVB failure by far.
- Leaking check or air inlet. Worn seals spray at start-up and will not hold the required differential.
- Freeze damage. Water left in the bonnet over winter cracks it. Visible on the first pressurisation.
- Wrong height. A PVB installed lower than the highest head is an installation error, not a test failure, but the Region can require it be corrected.
A failed device follows the same path as any other: reported, repaired or replaced by a licensed plumber (often the irrigation contractor’s plumber), and retested. See failed backflow test: what happens next.
Testing irrigation devices across Durham Region
Spring is the busy window and the drive between Brock, Uxbridge and the lakeshore towns is real, so we batch irrigation testing by area. If you manage several properties, send the list once and we schedule the route. Same program and by-law in every municipality. More on how it works and pricing, or read our irrigation and landscape page for the property-management angle.
PVB questions
When should an irrigation backflow preventer be tested?
At spring start-up, once the system is pressurised and before the first watering cycle. Testing it then catches winter damage and gets the report filed before the Region's notice cycle. If your notice has a due date earlier than your start-up, tell us and we will schedule around it.
Is a PVB the same as an RPZ?
No. A PVB has one check valve and an air inlet, and it only protects against backsiphonage (supply pressure dropping). It cannot handle backpressure, so it must sit above the highest sprinkler head. An RPZ has two checks and a relief valve and handles both conditions. Irrigation with chemical or fertiliser injection needs an RPZ, not a PVB.
Do residential lawn sprinklers in Durham need annual testing?
The by-law targets industrial, commercial, institutional and multi-residential properties. A single-family home is generally outside the program. Irrigation on a condo corporation's common property, a plaza, a school, or a church is inside it. If you are not sure whether your property is covered, the notice from the Region settles it: if you got one, you are.
My PVB sprays water when the system turns on. Is that a failure?
A brief spit from the air inlet as the line pressurises is normal. Water that keeps coming out means the check or air inlet is not seating, and it will not pass a test in that state. Sometimes debris flushes out and it stops. Often it needs a rebuild kit.
Book a PVB test
Tell us the address and where the device is. We schedule the test, tag it, and file the report with BSI Online.