Print this pageContamination from Surge and Transient Pressures
Low pressures (caused by surge pressures) can occur in trunk mains and networks, which in some instances can fall below atmospheric pressure. Recent studies of operating networks show that over 43% of networks experience sub atmospheric pressures and that these can significantly increase the risk of contamination. The studies showed that in 12 out of the 13 cases the pump operations caused the problems but we also have experience of valve operations causing low pressures.
The risk of contamination is higher when the mains or distribution systems have leakage – the high surge pressures causing the leaks and the low surge pressures causing ingress and hence increasing the risk of contamination. So the risk of intrusion of external contaminants is greater through systems with high leakage, in addition to submerged air valves, faulty seals or other openings.
With many water distribution systems experiencing 10-32% leakage it is easy to comprehend the risk of contamination.
It is often easier to prevent the low surge pressures that totally control all of the intrusion points. So surge suppression techniques such as air vessels or soft stop devices have been used to minimise the risk of contamination.
