What is a DCV (double-check valve) and where is it typically installed in a cold water system?

• A. A backflow prevention device with two checks and a relief path; installed on lines protecting against backflow from cross-connections, typically on the service line or feeder to a risk area.
• B. A device to measure pressure; installed at the main service entrance only.
• C. A filter for particulates; installed after the heater.
• D. A valve for isolation of a branch; installed downstream of fixtures.

Answer: (A)

A DCV is a backflow prevention device that uses two check valves with a relief pathway. Its job is to stop water from flowing backward into the potable cold-water supply if pressure changes or a cross-connection creates a backflow condition. The relief path venting or drainage provides a safe outlet if backflow occurs, preventing contamination of the supply.

In a cold water system, you install a DCV on lines where a cross-connection could allow dirty or non-potable water to be drawn back into the main supply, typically on the service line or feeder that supplies a risk area. This placement protects the broader system by guarding the supply before it branches to potential cross-connection points.

The other options don’t fit because a device that measures pressure, a filter for particulates, or a simple branch isolation valve does not provide backflow protection. A DCV is specifically designed to prevent reverse flow and safeguard potable water.