Backflow assembly testing and repairs

What a backflow preventer does

When pressure in the city main drops, from a watermain break or a hydrant being opened, the flow can reverse and draw building water toward the street. A boiler loop, a carbonator, an irrigation line or a chemical feed could end up in the public supply. A backflow assembly uses spring-loaded check valves, and on higher-hazard sites a relief valve, to stop that.

• Double check valve assembly (DCVA): two checks in series, used on moderate hazards.
• Reduced pressure assembly (RP): two checks plus a relief port that dumps water if both leak.
• Premise isolation: one assembly protecting the whole building at the water entry.
• Zone or fixture protection: smaller devices on boilers, soda lines, hose bibs.

How a test is done

We close the downstream shut-off, attach a differential pressure gauge to the test cocks and read each check valve and the relief valve against the minimum values. A test takes the water off for a short time, so we book it when the building can cope.

When an assembly fails

• Debris on a check seat: flushed and retested.
• Worn rubber parts: rebuilt with the manufacturer’s kit.
• Cracked body or seized shut-offs: replaced.

The City’s backflow program

Toronto’s water bylaw requires backflow prevention on many industrial, commercial, institutional and multi-residential properties, with testing on a set schedule and reports submitted to the City. The program gets updated, so confirm the current schedule with Toronto Water and file a copy of each report.

What’s included

How the visit runs

1. 1
   Locate

   Assembly, test cocks and shut-offs found and labelled.

2. 2
   Test

   Differential gauge readings taken and recorded.

3. 3
   Repair

   Rebuild kit or new assembly if a check fails.

4. 4
   Report

   Results written up for your records.

Common questions