Types of backflow preventers
Three assemblies cover almost every ICI and multi-residential property in Durham Region. Which one you have depends on the hazard the Region assigned to your connection. All three are tested every year.
What a backflow preventer does
The annual test on these devices goes by several names: backflow test, backflow inspection, device test. Same procedure. Water in the municipal main is meant to move one way: from the Region's plant, through the main, into your building. A cross-connection is any point where the building's plumbing could push or pull water back the other way, carrying whatever is on your side (boiler chemicals, dish machine detergent, irrigation water off a lawn) into the drinking supply. A backflow preventer is a mechanical assembly on that connection that only lets water move forward. Because it is mechanical, it wears, and because it wears, Durham Region's By-law 24-2018 requires it to be tested annually by a qualified tester.
Two ways water flows backward
The device you need depends on which of these can happen at your connection.
- Backsiphonage. Pressure in the main drops (a main break, a hydrant opened for firefighting or flushing) and water is sucked backward out of your building. Any device stops this.
- Backpressure. Pressure on your side rises above the main (a booster pump, a boiler, elevated piping, a well on the same site) and water is pushed backward. Only devices with a check valve rated for backpressure stop this. A PVB does not.
The three testable assemblies
| Assembly | Hazard level | Protects against | Where you find it | Tell-tale sign |
|---|---|---|---|---|
| DCVA Double check valve assembly | Moderate | Backsiphonage and backpressure | Domestic service to offices, plazas, apartments, warehouses | Two check bodies in a row, four test cocks, no drain |
| RPZ Reduced pressure principle assembly | Severe | Backsiphonage and backpressure, fails safe | Boiler rooms, medical and dental, restaurants, car washes, process water | Relief valve underneath that can discharge water; sits over a drain, never in a pit |
| PVB Pressure vacuum breaker | Moderate (irrigation) | Backsiphonage only | Irrigation, outdoor hose connections | Upright unit with a canopy on top, mounted above the highest sprinkler head |
The Region's program page names the RP assembly for severe hazards and the double check for moderate hazards, following the CSA B64 series. Fire sprinkler lines have their own variants (DCDA and RPDA, with a bypass meter). We do not test fire lines in year one because isolating a sprinkler system is a Fire Code impairment; ask and we will point you to who does.
Non-testable devices are not what the notice is about
Dual checks, hose bibb vacuum breakers, and atmospheric vacuum breakers have no test cocks. They protect a fixture, not the premises, and they are not tested under the program. If you cannot find test cocks on the device you are looking at, keep looking for the assembly on the incoming service, usually near the water meter.
Premise isolation versus fixture protection
The device the Region's notice refers to is almost always the premise isolation assembly: the one on the water service where it enters the building, protecting the municipal main from everything inside. Some buildings also have zone or fixture devices deeper inside (on a boiler make-up line, a carbonator, a dental chair). Those may also be testable assemblies, and if the Region has them on file they get tested too. When you request a quote, list every device you know about; if the survey found more than one, the notice will list them.
What happens at the test, whichever type it is
- The tester locates the assembly and confirms the make, model, serial number and size against the Region's record.
- The shut-off valves are closed to isolate the assembly. Water to that line is off for the readings.
- A calibrated differential pressure gauge is connected to the test cocks. Each check valve (and the relief valve or air inlet, depending on type) is tested against the minimum values in CSA B64.10.1.
- Water is restored. Readings go on the report along with pass or fail.
- The report is submitted through BSI Online with the $25 filing fee. The Region reviews it and issues the tag.
Full walk-through on how it works. If a device fails, the path is on the failed test page.
Each device in detail
DCVA (Double check valve assembly)
Moderate hazard. Domestic water service to commercial buildings and plazas; Apartment and condo buildings.
About DCVA testingRPZ (Reduced pressure principle assembly)
Severe hazard. Boiler and mechanical rooms with chemical treatment; Medical, dental and veterinary suites.
About RPZ testingPVB (Pressure vacuum breaker)
Moderate hazard. Lawn irrigation systems on commercial, institutional and multi-residential properties; Landscape and sports-field irrigation.
About PVB testingDevice questions
How do I tell which type of backflow preventer I have?
Look at the shape and the label. Two check valve bodies in a row with four small test cocks and no drain port is a double check (DCVA). The same layout with a relief valve underneath that can discharge water, usually over a floor drain, is an RPZ. A single upright unit with a canopy on top, mounted higher than the sprinkler heads, is a PVB. The manufacturer plate on the body says the type and model. Our guide on finding your backflow preventer has diagrams and a room-by-room checklist.
Which backflow preventer does Durham Region require?
The by-law does not name a device by property type. It classifies the hazard using the CSA B64 series and requires the matching device: an RP assembly for severe hazards, a double check for moderate hazards. The Region determined your classification through the cross-connection survey and the notice tells you which device is on file.
Do all three types need testing every year?
Yes. By-law 24-2018 requires annual testing of every backflow preventer on an industrial, commercial, institutional or multi-residential property, regardless of type. Irrigation PVBs are tested when the system is pressurised, usually at spring start-up.
Do you test fire sprinkler line backflow devices?
Not in our first year. Section 9.1 of the by-law requires personnel approved by the Commissioner for fire protection system devices, and isolating a sprinkler line is a Fire Code impairment. Ask and we will refer you.
What about a dual check or a hose bibb vacuum breaker?
Those are non-testable devices. They have no test cocks, so there is nothing to measure. The Region's program is about testable assemblies (DCVA, RP, PVB, and their fire-line variants). If the only device on a connection is a non-testable one, it is not what the notice is asking about.
Can a backflow preventer be tested without shutting the water off?
Not properly. The test isolates the assembly using its shut-off valves and reads pressure across each check. Water to that line is off for the duration of the readings, roughly 30 to 60 minutes. Water to the rest of the building is unaffected unless the device is on the main service, in which case we book a time when a short interruption is acceptable.
Not sure what you have?
Send a photo of the device with your quote request. We identify it, tell you what the test involves, and book it.