‘Backflow’ is the flow of water in the opposite direction back into the water supply. Backflow preventers hold the pressurized fire sprinkler water line from flowing back into the municipal water line, a probable case if there is a loss of pressure from the municipal water line.
Backflow preventers reduce the chances of polluting the municipal water system through cross-contamination.
A Backflow Preventer
A backflow preventer is a mechanism devised to keep water inside a fire protection sprinkler system and other water-based arrangements installed on a property securing that it solely travels in one direction: from the water main into the pipes of the system.
Approved backflow assemblies have met the requirements of different certified testing agencies and each one is intended for particular applications. The most common assemblies include:
Double Check Valves (DCV)
Specifically outlined to prevent backflow in fire sprinkler systems, DCVs incorporate an inlet (upstream) shutoff valve, two independently operating spring-loaded check valves (usually inside a single valve body), four test cocks, and an outlet (downstream) shutoff valve.
Reduced Pressure Zones (RPZ)
RPZ backflow preventer assembly is used when antifreeze or corrosion inhibitors are introduced
RPZ backflow preventer assembly is most commonly used when hazardous chemicals like antifreeze or corrosion inhibitors are introduced.
RPZs dilate upon the double check valve notion. With a hydraulically operated relief valve that makes them exceptionally dependable, RPZs integrate an inlet shutoff valve, two spring-loaded check valves separated by a pressure differential relief valve, four test cocks, and an outlet shutoff valve.
Reduced Pressure Principle Detector Assembly (RPDA)
Primarily used in fire sprinkler systems, RPDA is a specially designed assembly composed of a line-size approved reduced pressure principle with a specific bypass consisting of a particular water meter.
Working of Backflow Preventer
Under normal conditions, the pressure between the two check valves is sustained at a lower pressure than the supply pressure. If either check valve shall leak the relief valve is devised to open and discharge water to the outside, ensuring backflow never eventuates.
The RPZ assemblies, while being reliable, encounter much higher pressure and volume loss than double-check assemblies. Inconsistent flow inline pressure (upstream or downstream) will prompt a properly functioning RPZ to periodically release small amounts of water. But during a backflow condition, a large volume of water will flow from the relief valve. And hence, for this reason, RPZ assemblies should not be installed in areas that are subjected to water damage.
Also, it must be noted that both types of backflow preventers scale down the available downstream water pressure. A proficient contractor must account for this when designing fire sprinkler systems.
Fire sprinkler systems in Backflow Preventers
Backflow from fire protection systems can contaminate the potable water
Fire sprinkler systems must have backflow preventers. Municipalities, water purveyors, and plumbing inspectors have outlined, enforced, and set forth plumbing codes and directives for installing backflow preventers to protect local drinking supplies. Therefore one should check and acquire knowledge from the local water authority about the particular requirements for backflow preventers in an area.
Backflow from fire protection systems can contaminate the potable water. Thus, it is essential to install backflow preventers in the sprinkler systems. By doing so, one can prevent avoidable accidents and meet code requirements in the area.
So, ensure to check with the local authority having jurisdiction (AHJ) on the exact backflow prevention requirements in the area, system, and occupancy type.
