PLUMBING INFORMATION - What is a Double Check Valve? - When is a Double Check Valve - Needed - Fitted?

Double Check Valve.

A double check valve allows water to flow through it in one direction only.
It is fitted where there is a danger that backflow of water will contaminate the supply.

An example would be an outside tap connected to a garden hose pipe.
If the end of the hose was left in a pond, it would be possible that
negative pressure on the supply side could suck pond water back into the mains.
This contaminated water could then be accessed by other users further down
the supply line from their normal kitchen or bathroom taps.

It is called a double check valve because there are two valves inside the fitting
as a safety feature. It is very unlikely that both valves will stop working.

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