The importance of protecting the main water system with backflow prevention valves
PROTECT THE QUALITY OF MAINS WATER BY PREVENTING BACKFLOW
Potable water from the mains supply may be subject to pollution caused mainly by the contaminated fluids flowing back from plumbing installations connected directly to the mains supply. Backflow can be attributed to a variation in the pressure difference that causes a consequent inversion of the normal direction of flow at certain point of the installation. This phenomenon, termed “backflow”, occurs when:
- the pressure in the main water system is lower than that in the downstream circuit (back siphoning) due to a break in the pipework of the main water system and the consequent maintenance work, or when significant quantities of water are drawn by other utilities connected upstream, such as fire-fighting systems.
- the pressure in the plumbing circuit receiving the supply rises (counter pressure) due, for example, to water being pumped from a well
INSTALL BACKFLOW PREVENTION DEVICES ACCORDING THE RISK ASSESSMENT OF BACKFLOW POLLUTION
Given the potential danger of the phenomenon and the requirements of current regulations, the risk of pollution by backflow must be assessed on the basis of the type of system and the characteristic of the medium that flows in it. An appropriate backflow protective device must be selected on the basis of that assessment performed by the system designer and the mains supply Company. The device must be located along the supply line at those points at risk of backflow which would be hazardous to human health. The Protection Matrix below was drawn up on the basis of the indications provided by European standard EN 1717 and national regulations. Obviously, the table is not exhaustive.