WHAT IS BACKFLOW?
Backflow is the reversal of flow along a supply pipe so that water travels in the
opposite way to the intended direction.
This can create a hazard to water users, as contaminated water can be drawn back along
a supply pipe into the drinking water supply.
WHY DOES BACKFLOW HAPPEN
Backflow can happen for a number of reasons, but two in particular:
-
When the pressure along a water supply pipe drops suddenly at one end:
For example, in the case of a burst pipe where water escapes from the point of the
burst and the sudden loss of pressure that was previously pushing water through the
pipe causes water to be pulled or syphoned back along the pipe towards the burst.
-
Where water is moving up through a vertical pipe:
This can be due to the effects of syphonage or because the water is being heated and
is travelling up the pipe in response to convection currents.
If the syphonic effect stops, water may fall back down the pipe. In the case of heated
water in a pipe, if the pipe is wide enough, heated water may travel up one side of
the inside of the pipe and cooler water down the other side (known as 'single pipe
circulation').
HOW TO PREVENT BACKFLOW
Backflow can be prevented by devices such as check valves and air
gaps.
The type of backflow prevention required will depend on the risk of contamination
from backflow and the nature of the contaminant.
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