Double Check Valve vs Check Valve: Backflow Basics

These terms get mixed up constantly, and getting them wrong can mean a failed inspection or an unprotected water supply. A single check valve, a double check valve, and a certified backflow preventer are three different things. Here is the plain-language difference and how to choose.

Single check valve

One check element that stops reverse flow. Perfect for protecting a pump, holding prime, or preventing backflow in a process line. It is a mechanical device, not a certified assembly, so it is not what codes require for potable-water cross-connection protection. See all check valve types.

Double check valve

Two independent check elements in series in one body. The redundancy means if one fouls or leaks, the other still holds. In dosing and metering, a double check gives extra assurance against back-siphoning of chemical. Note that a plain double check valve for process use is different from a certified Double Check Valve Assembly (DCVA) used for potable backflow protection.

Backflow preventer (the certified assembly)

When code requires protecting a drinking-water supply from cross-contamination, it specifies a tested, listed assembly: a Double Check Valve Assembly (DCVA) or, for higher hazard, a Reduced Pressure Zone (RPZ) assembly. These have test cocks and shutoffs, must be installed by qualified people, and are tested and certified periodically. A single or double check valve from a general catalog is not a substitute where a certified assembly is required.

How to choose

If you are protecting equipment, a pump, or a process line, a single or double check valve is the right, economical answer. If you are protecting a potable-water supply and an inspector is involved, you need the specific certified assembly your local code calls out, installed and tested to standard. When in doubt, ask your authority having jurisdiction which class of protection your application requires.

Shop check valves

For process and equipment protection, browse all check valves or the metering pump check valves built for dosing systems. For certified potable backflow assemblies, consult a specialist supplier and your local code.