Filtration & Coagulation Flashcards
What does ‘filtration rate’ refer to?
The speed at which the circulating water is traveling vertically downwards through the filter.
There are three categories of filtration rate. What are they?
High rate
Medium rate
Low rate
The filtration rate is usually expressed as m3/m2/hr. What does that mean?
Metres cubed (the flow rate), divided by metres squared (the surface area of the filter, per hour.
The recommended filtration rate is the medium rate. What is the medium rate filtration range?
11 - 25m3/m2/hr
What does the term ‘backwash’ mean?
The process of reversing the flow of water through the filter and away to drainage.
How often should the filter(s) be backwashed?
Depends on usage, but a swimming pool is usually once or twice a week and a spa pool is every day.
What happens to the pressure at the inlet to the filter as the filter accumulates more pollution?
It increases, ie, the needle on the gauge will go up.
What happens to the pressure at the outlet of the filter as the filter accumulates more pollution?
It decreases, ie, the needle on the gauge will go down.
How can the filter inlet and outlet pressure be used to determine when to do a backwash?
When the difference between inlet and outlet pressure reaches a pre-determined level, it’s time to do a backwash.
Backwashes should always be done last thing, not first thing. Why?
Doing it last thing gives the filter time to ‘ripen’ overnight.
What is filter ‘ripening’.
As the filter traps pollution within the sand bed, the gaps between the grains of sand get narrower. Smaller gaps mean better filtration.
