Answer: A backflow prevention device is a valve assembly that is installed in the water piping that feeds the sprinkler system. It prevents corrosive materials in the sprinkler piping from getting out into the city water supply.
The assembly consists of two check valves sandwiched between to control valves. The formal name for this valve is a “Double check valve assembly” or “DCVA” for short. The DCVA is the most basic valve and is widely accepted by the water departments. But some water departments may require a “Double Detector Check Valve Assembly” or a DDCVA. This has a bypass meter on the side of the assembly that records the quantity of water that passes through the DDCVA.
If you have a DCVA or a DDCVA in your building for your fire sprinkler system, check with your local authorities about required inspections on your assembly. Many jurisdictions require it to be inspected every year.

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Double Detector Check Valve