Swimming pool filters remove dirt and debris from the water. The most common type of filter uses #20 silica sand as the filtering media. Grains of sand have jagged edges that snag particles as they flow by. Spaces between each grain begin to fill up with trapped debris, reducing the available paths for water to flow. This reduction in paths produces an increase in pressure inside the canister holding the sand. When the pressure gauge on the canister increases by 8-10 lbs. of pressure over the beginning pressure, it is time to backflush the filter and remove the debris.
Turn off the pump.
Depress the handle of your multi-port valve by applying firm pressure until it turns freely without scraping. Turn the handle until it is in the backflush or backwash position, and release the tension on the handle.
Check your backflush hose connection to make sure that the hose clamp is secure. A loose clamp will not stand the force of the wastewater exiting the pool and can cause flooding if it pops off. Since your backflush hose always remains connected to the waste port of your filter system, it is easy to overlook. Periodically, make sure that the far end of the backflush hose, which is normally about 50 feet from the pool, is still directing the waste water where you want it to go on your property.
Turn on the pump, which will reverse the flow of water inside the canister and clean the sand of trapped debris. Run the pump until the water flowing through the canister's sight glass changes from dirty to clear.
Turn the pump off to stop the rapid loss of water out of the pool.
Depress the handle on the pump and turn it to the rinse position.
Turn on the pump for 20-30 seconds, then turn it off. This action settles the sand and makes sure that none of it is in the wrong compartment inside the multi-port valve. Without this step, sand may end up on the bottom of the pool.
Turn the pump off.
Add water back into the pool, making sure to test and treat it chemically. The water level should be at the middle of the skimmer opening.
Turn the pump's multi-port valve to the filter position and turn the pump on.
Make note of the starting pressure on your pressure gauge and treat it as your new benchmark for backflushing. Backflush only when the pressure rises 8-10 lbs. higher than where it is now.