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How Does a Pool Pump/Filter System Work?

How Does a Pool Pump/Filter System Work?

Pool Maintenance  |  Options and Accessories  |  Swimming Pool FAQs  |  Swimming Pool Accessories

Technology is hard. It's even worse when you can't pick the equipment out of a lineup. But we're here to make your life easier, in every way we can. So today... let's talk filter systems.

Heads up: At River Pools we manufacture and install fiberglass pools only. However, this filter system guide applies to all three pool types.

 

illustration of pump/filter system

How Your Filter System Works: The Short Answer

Your pump pulls the pool water from the skimmer(s) on the pool wall and the main drain(s) on or near the bottom of the pool.

The water flows through the pump to the filter, which removes dirt, debris, and (if the filter is good) bacteria.

After the water is filtered, it flows through the plumbing to the heater (if you have one) and then the salt chlorine generator (if you have a saltwater pool).

The clean water returns to the pool through the return jets on the pool walls.

 

 

The Skimmer and Main Drain

pool skimmer on our C40 pool

These features are probably already familiar to you, but just to recap.

A skimmer is the rectangular opening at the top of the pool wall, right below the coping. (The water level should generally be about halfway to two-thirds up the skimmer.)

A main drain is the big ol' drain at the bottom of the pool.

Side note: You may not have a main drain—they're becoming less common in residential pools, in favor of only skimmers. This is because for smaller pools, main drains aren't always necessary.

Water flows through the skimmer and the main drain towards the pump and filter to be cleaned.

 

The Pool Pump

A pool pump generally has a big, round part at the front and then extends backward.

SuperFlo VS pool pump

That big, rounded part at the front (covered by a lid) is the strainer pot. It looks and acts, predictably, like a strainer.

A spinning impeller inside the pump pulls the water in from the pool.

This water hits the first part of the pump, the strainer pot, which catches any major debris.

After the water goes through the strainer pot, the impeller pushes it on to the filter.

 

The Pool Filter

All pool filters fall in one of these three categories:

  • Cartridge filter
  • Sand filter
  • Diatomaceous earth (D.E.) filter

A cartridge filter uses cartridges—big sheets of polyester cloth or paper folded accordion-style—to catch debris. Some of these filters only need a single cartridge; others need multiple.

(Here at River Pools, most of our customers get a cartridge filter with their fiberglass pool.)

single-cartridge filterillustration of cartridge filter and cartridgescartridge filter photo

A sand filter is straight-up a tank full of sand. Slotted lateral pipes at the bottom disperse water evenly through the sand to catch debris.

illustration of sand filters

D.E. filters use 8–10 filter grids/fingers covered in D.E. powder (diatomaceous earth, which is basically fossil dust) to catch debris. The fingers may look like hanging stalactites or overlapping curved shutters, depending on the model.

illustration of D.E. filters

 

A quick note about filter quality!

Dirt and debris are measured in microns, which is short for micrometer—one-millionth of a meter. Yes, that's a lot of zeros.

For reference:

  • 1 millimeter: 1,000 microns
  • Human hair: 50–100 microns
  • Pollen: 30 microns
  • Household dust: 4 microns
  • Bacteria: 2 microns

A filter's "micron level" tells you the size of the smallest debris it catches, so a lower micron level means better filtration.

 

The Pool Heater

Pretty much all pool heaters are one of these three types:

  • Electric heat pumps
  • Solar heaters
  • Natural gas/propane heaters

(Solar heaters usually look like solar panels and are outside the scope of basic pump/filter system plumbing. For our purposes today, we're talking heat pumps and natural gas/propane heaters.)

A pool heater tends to look big and clunky. Fair enough; it has a lot of work to do.

pool heaterheat pump control panel

You can choose to get a heat pump with a chiller feature. That's especially awesome if you live in a toasty climate, have a shallow pool, or use an automatic pool cover.

Fun fact: About 19 of 20 of our customers who install heaters choose heat pumps because of their dependability and low operating cost.

 

The Salt Chlorine Generator

Heads-up: If you have a traditional chlorine system in your pool, you don't have to worry about this section. You don't have a salt chlorine generator, so skip on ahead to return jets. Or read this section anyway. Whatever floats your goat.

For a saltwater pool, instead of adding chlorine to the pool water, you add salt, and the generator converts it to chlorine.

(It's about as salty as a teardrop, nowhere near ocean levels.)

The salt chlorine generator has multiple parts:

  • The cell
  • The control board

The cell is what's connected to the plumbing pipes. The control panel is usually a little farther away.

Pentair IntelliChlor salt chlorine generator cell

After being filtered, your pool water flows through the cell. Inside, a series of metallic grids with a low-voltage current create a reaction that converts the salt down to little bubbles of pure chlorine. This pure chlorine reacts with the water to form hypochlorous acid, which is what cleans your pool.

Cool, right?

(To learn more about saltwater pools, check out our article What is a Saltwater Pool? Chemistry, Lifespan, Cost, & More.)

 

The Return Jets

Return jets... well, they return the filtered water to the pool.

Spa jets are a variant of this.

returns for spa jets

I'm trying to think of a way to make it more complicated, but it's not.

 

Pop quiz!

Let's see if you can pick out the 3 major parts of your filter system: the pump, the filter, and the salt chlorine generator.

(It's an open-book quiz. We included arrows.)

Recognize them here?

pool filter system (version 1)

How about in this configuration?

pool filter system (version 2)

What about this "mysterious" fourth feature? It sure does turn up the heat on the challenge...

pool filter system (version 3)

Honestly, it just feels cool to be able to look at a mess of plumbing equipment and say, "Ah yes, there is the filter! And there is the pump! I know so much about pools. Ohoho!" (That last bit is where you chortle like a baron.)

 

Want to learn more about pools?

I mean, you're basically a pool pro now. But it never hurts to expand your repertoire!

Our blog articles and our YouTube channel videos answer every question you may have about pools, throughout both the buying process and lifetime ownership. Check them out, and then impress your friends and family with your pool knowledge!

Based near Richmond, VA, River Pools specializes in manufacturing and installing fiberglass pools because we're firm believers in their long-term quality—they're beautiful and durable, require little maintenance, and have a quick installation time to boot.

Our pools are also available nationwide through our River Certified Dealers, who install them using the above-and-beyond standards of The River Pools Way.

Request Pricing for Your Fiberglass Pool

We're excited to help you any way we can!

Next: Where Should I Locate My Pool Filter System?

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