Backflow Prevention
Backflow is the unwanted reversal of water flow within a system. Without protection, it can draw contaminated water back into the public supply. Here is how it is prevented.
How backflow happens
Backflow can occur through back-pressure — where pressure in a downstream system exceeds the supply pressure, pushing water back — or back-siphonage, where a drop in mains pressure (for example during a burst main) draws water backwards. Either can pull contaminants into the drinking water supply if no protection is fitted.
Types of backflow prevention device
Single check valve (Type A)
Suitable for low-risk (category 2) situations where a simple non-return barrier is adequate.
Double check valve (Type A)
Two check valves in series; suitable for category 3 risks in many installations.
Reduced pressure zone (RPZ) valve
The most robust mechanical device; provides a relief path to atmosphere. Suitable for fluid category 4, and for fluid category 5 where the water undertaker has granted written consent.
Air gap
A physical, unobstructed gap between the outlet and the fluid. The standard solution for the highest-risk (category 5) fluids where RPZ valve consent has not been granted.
Not sure which device you need?
We assess the actual risk on your site and specify the correct, compliant protection — no over-specifying, no gaps.