The learner should understand what Backflow is and how it occurs.
What is a Backflow and How must we protect against it?
The movement of any substance in any direction is called flow. So why the term backflow when water moves from an installation towards the municipal potable supply? Firstly, it is assumed that the water in any installation originates from the municipal supply and so the water that flows back towards there is viewed as flowing back and thus called "Backflow".
What has happened to the water that makes it unsafe to return it from where it comes? Firstly, we need to take cognizance of the fact that once the water passes past the water meter it now becomes the homeowner's responsibility and the municipality no longer has control over what happens to it. Once they have lost control over what happens to the water, they do not want to let it back into the municipal system.
We could let the water back into the municipal system if it was tested and certified as SANS 241 quality compliant, but we know that is not practical.
How does Backflow occur?
Simply put, the backflow of water in a plumbing system will occur in a number of instances:
- During maintenance of a system and a siphon is created in part of the system causing a reverse flow.
- When the pressure downstream of the source of supply is increased causing water to flow in the opposite and unintended direction.
- When pressure is lost at the source of supply or pipe bursts simply causes the system to drain to the low-pressure area.
- During Firer Fighting when there is a large draw-off on a communication or service pipe (rare).