Back Flow Preventers

Double Check + Reduced Pressure Zone Assembly

  • Backflow happens when there is undesirable reversal of flow of a liquid, gas, or suspended solid into a portable water supply. Two factors contribute to backflow: Backsiphonage and backpressure.
  • Backsiphonage: Occurs when there is negative pressure in supply piping – Under-sized pipes, pipeline breaks and high withdrawal rate (e.g. when fire hydrant is used) can create vacuums that cause backsiphonage.
  • Backpressure: Occurs when a pressure higher than the supply is created in the downstream piping, this can be caused by pumps, thermal expansion and elevation.
  • A backflow preventer protects portable water pipelines from contamination and pollution from a backflow. There are two types of backflow preventers – the double check valve (DC)and the reduced pressure zone assembly (RPZ).
  • The issues with a double check valve is that during the event of a malfunction of the valve closure or if there is a debris stuck, the valve cannot close completely. Also, there is no way to verify whether a failure has occurred until it has been checked by someone
  • Reduced pressure zone assembly valves on the other hand, work like a double check valve but with an additional relief valve. When a backflow occurs, both check valves close and the relief valve opens to evacuate the water. In case a debris gets caught in between the check valves, during backflow, the siphoning water can still be discharged through the relief valve.