Double check valve assembly (DCVA) testing

What a double check valve assembly is

A double check valve assembly (DCVA, sometimes just “double check”) is a backflow preventer with two independent, spring-loaded check valves in series inside one body, a shut-off valve on each end, and four test cocks. Water can only move one way through it. If pressure on the building side ever rises above the supply side, or if the supply pressure drops, both checks close and stop water from flowing back into the municipal main.

It is the most common device on the domestic water service of commercial and multi-residential buildings in Durham Region. If your property is a plaza, an office building, a warehouse, or an apartment or condo tower without boilers or chemical processes on the water system, there is a good chance the device on your incoming water line is a DCVA.

Where a DCVA is used, and where it is not

Durham Region’s by-law follows the CSA B64 series standard, which sorts properties and connections into hazard levels. A DCVA is approved for moderate hazards: situations where a backflow event would make the water unpleasant or unsafe to drink but is not expected to carry substances that are dangerous at any concentration. The Region’s program page describes moderate hazard as connections that could reduce the aesthetic quality of the water.

Typical DCVA installations:

Property or connection	Why a DCVA fits
Domestic water service to a commercial building	Premise isolation for a moderate-hazard building
Apartment or condo domestic service	Multi-residential premise isolation
Retail plazas and strip malls	Shared service, tenants without process water
Some irrigation systems	Where the piping layout does not allow a PVB

A DCVA is not the right device for boiler rooms with chemical treatment, medical or dental suites, car washes, food processing, or anything the Region classifies as a severe hazard. Those need a reduced pressure principle assembly (RPZ). If a survey found a severe hazard on your property and you have a DCVA, the Region will ask for an upgrade.

What the annual DCVA test checks

The test uses a calibrated differential pressure gauge connected to the four test cocks. Working through the assembly, the tester confirms:

1. Check valve 1 closes tight against reverse flow and holds a differential pressure at or above the minimum in the CSA B64.10.1 test procedure.
2. Check valve 2 does the same, tested independently.
3. The shut-off valves on both ends close fully. If a shut-off leaks, the tester cannot isolate the checks and the device cannot pass until the valve is repaired.
4. The test cocks open and close and are not seized or leaking.

Each reading goes on the report along with the device make, model, serial number, size, and location. The report is submitted through BSI Online, the Region reviews it, and a test tag is issued for the device. BSI charges a $25 filing fee per report, subject to annual increases, and a quote should say whether that fee is included.

Why double checks fail

Most DCVA failures are dull, mechanical, and fixable:

• Fouled checks. Scale, grit, or debris sits on the rubber disc so it cannot seat. Common after main breaks or construction nearby, and more common in older buildings.
• Worn discs and seats. Rubber hardens and cracks over years of cycling.
• Weak springs. The spring no longer pushes the disc closed with enough force to hold the minimum differential.
• Shut-off valves that will not hold. Old gate valves are the usual culprit. The device may be fine, but it cannot be proven fine.
• Seized test cocks. Not a failure of the device, but the test cannot be run until they are freed or replaced.

If a check fails, the device is reported as failed. Under By-law 24-2018 the failure must be reported to the Region promptly, the device must be repaired or replaced by a licensed plumber, and it must be retested. Our failed test page walks through that path and how repair is coordinated.

Getting a DCVA tested in Durham Region

Testing is arranged for the whole Region under one program, so the process is the same in Oshawa, Whitby, Ajax, Pickering, Clarington, Uxbridge, Scugog and Brock. Tell us the address, roughly how many devices are on site, and whether you have a notice with a due date. We book a slot (early morning or after-hours if the building needs it), coordinate access with the super or facility contact, and make sure the report is filed. Full details on how the visit works and what testing costs.