Pool Plant Courses - Blog

If you have the filter manufacturers instructions, refer to those as they will inform you of how often a backwash needs to take place. Quite often though, these instructions have been lost long ago, so this article will outline some recommendations. What happens to a filter over time is that as it does its job and collects within it all the pollution and contaminants that you don't want getting in your pool, it becomes blocked up. This process is actually helpful towards the beginning of the cycle as it causes narrower gaps between sand grains (known as pores). This means that the filter will be capable of trapping smaller particles. This process is known as 'filter ripening'. As this process is happening, the resistance to flow encountered by the pool water as it enters the top of the filter will increase. At the same time, the force at which the water comes out of the filter at the bottom decreases. It's a bit like when you get a kink in a hosepipe; you'll only get a trickle out of the end of the hose, and the pressure will build up behind the kink. There are usually pressure gauges located on the inlet and outlet of a filter and their job is to tell the pool plant operator what the pressure differential (or head loss) is. As the pressure increases at the inlet, the needle on the gauge will move up and as the pressure at the outlet decreases, the needle will move down. By reading the values at the gauges and comparing them, you can work out the pressure differential across the filter bed. As a rough guide, when this pressure differential reaches 0.4bar, it's time to do a backwash. What usually works better from an operational point of view is to do a backwash every week. Keep an eye on the pressure differential and review the policy if needs be.