Pool Filter Basics

Today we’re going to talk about how a swimming pool filter system works.  There is a pump timer, a swimming pool pump and a filter.  We’ll talk about the function of the pump, the filter, the plumbing and how all this works together.

Water travels from the pool to the pump. The water comes in through two pipes.  One comes from the pool skimmer and the other comes from the main drains at the bottom of the pool. The water is pulled into the pump on the suction side.  Before entering the pump the water travels through a basket called a strainer pot.  The basket is a secondary means for filtering the water to prevent debris from getting into the pump chamber where the impeller spins.  The water leaves the pump on the discharge side or “pressure side” of the plumbing.  The water is pushed from the pump into the filter.  The filter serves to remove dirt and debris from the water.  The clean water then leaves the filter and, in some cases, passes through a chlorinator and back to the pool.  It is best to chlorinate the water after it leaves the filter so that less chlorine gets into the pump and filter which can be bad for the equipment.

There are three popular types of filters.  One is a sand filter.  The sand collects and traps debris.  To release the debris the sand filter needs to be backwashed.  Another filter is a cartridge filter.  They have a greater surface area and are lower in maintenance.  One or two times per season a cartridge filter needs to be hosed off and cleaned.  The last type of a filter is a DE or diatomaceous earth filter.  DE is a fine powder that coats the grids of the filter housing.  DE filters are the best for trapping the smallest of debris.  DE filters also need to be backwashed occasionally and the DE power needs to be replaced with each backwash.

Backwashing a filter is the simple process of running the filter in reverse and flushing the filter of debris.  You know it is time to backwash when the pressure in the filter rises above 20 psi.  This means there is too much debris in the filter and water is struggling to pass through the system.   If backwashing doesn’t work or pressure increases rapidly it may be because the pool has a lot of debris or the filter needs to be manually cleaned.

Sometimes after your pump has been off for a long period of time it can be difficult to reprime it.  This is because all the water has drained from the filter and the plumbing.  To facilitate priming, completely close the main drain valve.  Fully open the skimmer valve.  Place the filter valve in the circulate position.  Then turn the system on.  This will isolate the filter from the circuit thereby asking the pump only to prime the plumbing.   Within a few minutes you should have a full and constant water flow through the pump.  Once this has been established, quickly shut off the pump.  Move the filter valve into the filter position and restart the pump.  The prime will continue and fill the filter.  Don’t forget to bleed the air from the filter when prime is established.