How to Backwash a Pool Filter
If you have a swimming pool, or are building one, you've certainly heard of filter backwashing.
But what is pool filter backwashing? How do you do it? And when?
Danny, your pool expert, answers.
What is backwashing?
Backwashing is a special operation, enabled by the multiport valve, which reverses the water flow inside the filter, allowing the removal of previously trapped particles. The water flows through the sand bed in reverse, from bottom to top. This water is not returned to the pool but discharged.
When should backwashing be performed?
Backwashing should be performed when the amount of dirt particles, debris, and pollutants is so high that it impairs the filter's operation. You can notice this by observing the water flow from the return jets: when the filter is clogged, the jets discharge little water. Another way to tell if the filter needs cleaning is to check the pressure indicated by the pressure gauge on the filter or the multiport valve. Below 0.8 atmospheres, the filter does not need cleaning; above one atmosphere, the filter is likely clogged and thus requires backwashing.
How to backwash a sand filter?
The filters commonly used for purifying swimming pool systems are, nine times out of ten, sand filters. This type of filter, which is very effective and robust, works by trapping dirt on its sand bed. As dirt accumulates, the water flow decreases to the point of compromising water recycling and purification (too little water passes through the filter). At this point, all trapped debris and dirt must be removed. Let's see step-by-step how to perform the backwashing operation.
Backwashing – procedure
- Turn off the pump;
- Set the multiport valve to the "Backwash" position, opening the drain valve, if present;
- Turn the pump back on;
- Check that water is actually flowing out of the filtration circuit (discharged outside or into the sewer);
- Wait until the water coming out is clean; if you cannot check the clarity of the water, then check the sight glass on the multiport valve. Backwashing usually takes about 2 or 3 minutes to clean the filter. Once backwashing is complete, turn off the pump;
- Set the multiport valve to the "Rinse" position and wait a few seconds for the sand to re-compact inside the filter;
- Turn the pump back on for about 20 seconds; this allows the first water passing through the filter to drain, carrying away any remaining pollutant particles in the filter;
- Turn off the pump;
- Set the multiport valve to "Filter," close the drain valve, and turn the pump back on.