Pool Filter Backwashing: A Step-by-Step Multiport Valve Guide

Before switching to backwash, know what each position does. FILTER (Filtration): the normal operating position; water passes through the sand and is cleaned. BACKWASH (Backwashing): reverses the flow and sends the dirt to waste.

RINSE (Rinsing): after backwashing, it resettles the sand bed and sweeps the remaining dirt to waste; if skipped, sand escapes into the pool, which we explain separately below. WASTE or DRAIN (Waste/Drain): sends water directly to waste without passing it through the filter at all; used when emptying the pool or when vacuuming the floor after flocculation.

RECIRCULATE (Recirculation): returns water to the pool without passing it through the sand; used when the filter is faulty or during some chemical treatments. CLOSED (Closed): shuts off all flow, is used for equipment maintenance, and the pump is never run in this position. The pump is stopped every time before the valve is turned; a valve turned while the pump is running damages its seals and the sand bed.

The gauge is the pressure indicator on the filter and shows how clogged the sand bed is. When the filter is clean, that is, just after a backwash, the reading on the gauge is your clean starting pressure; note this value, because it is your reference.

As the sand bed fills with dirt, water passes through with more difficulty and the pressure rises. The general rule is this: when the gauge rises approximately 0.3-0.5 bar above the clean starting value, it is time to backwash. For example, if the clean pressure is 1.0 bar, you should backwash when the gauge reaches 1.3-1.5 bar. This rise is the most reliable sign that the sand bed is clogged.

Manage the pressure with the gauge, not the calendar. 'I backwash every week' is not a good rule; with heavy use it may be needed more than once a week, and in quiet periods once every two weeks. Reading the gauge regularly and deciding by the pressure threshold both protects the filter and prevents unnecessary waste of water and energy.

Step one: stop the pump. Never turn the valve while the pump is running. Step two: prepare the waste line; open the backwash hose or set the waste valve to the appropriate position, because dirty water will be discharged. Step three: set the multiport valve to the BACKWASH position.

Step four: start the pump and begin backwashing. Watch the water flowing through the sight glass on the valve; water that runs cloudy and dirty at first gradually clears. Continue backwashing until the water runs clear, usually 1.5-3 minutes. When you see clear water, the dirt in the sand bed has been dislodged.

Step five: stop the pump again. When the backwash is finished, do not switch the valve straight to FILTER; the RINSE step comes first, and we explain why in the next section. Because the dirty water is discharged, the pool's water level drops during backwashing; top up the water when the process is finished.

During backwashing the sand bed lifts, the grains shift and settle into an uneven position. If you switch the valve to FILTER and start the pump right after backwashing, loose sand from the lifted bed and the remaining dirt escape directly into the pool and cloud the water.

The RINSE step prevents exactly this. When the backwash is finished, stop the pump, set the valve to RINSE and run the pump for 30-60 seconds. This short rinse settles the lifted sand bed properly again and sweeps the last dirt particles left in the sand bed after backwashing to the waste line, not to the pool.

The classic scenario for those who skip RINSE is this: the filter has been cleaned but the water suddenly turns cloudy, and fine sand can even be seen on the floor. The cause is almost always the skipped rinse. When RINSE is finished, stop the pump, set the valve to FILTER and return to normal filtration. Check the gauge; it should now be back at your clean starting pressure.

The right measure is the pressure gauge: backwash when the pressure rises 0.3-0.5 bar above the clean starting pressure. In heavy summer use this may mean once a week or more often, and in quiet periods once every two weeks.

Events such as a storm, wind-blown dust, a day with many guests or vacuuming the floor after flocculation dirty the filter quickly and may call for an extra backwash. Also, if the clarity of the water is dropping and the flow is weakening, you can tell the filter is clogged even without looking at the gauge. Read the need for backwashing not from a single rule, but from both the gauge and the behaviour of the water.

Backwashing more often than necessary can also be a mistake; every backwash drains a considerable amount of water from the pool, and topping this water up means both water and chemical costs. Overly frequent backwashing also removes the light layer of dirt the sand bed needs for correct filtration. The measure is once again the gauge: do not wash before the threshold is reached.

The cleaning routine of a cartridge filter system (removing and washing the cartridge) corresponds to approximately 60 litres of water. The difference is close to 12 times; the two filter types differ in the water bill as well as in maintenance effort.

Waiting for the gauge threshold therefore also has a direct bearing on the water bill: every backwash done more often than necessary restarts a cycle of approximately 700 litres in a sand filter system. When choosing between a sand and a cartridge filter, this difference in water cost is an item to be weighed as much as ease of maintenance.