What Is A Pool Skimmer? How Do They Work?

pool skimmer in deep end of swimming pool

Whether you’re new to swimming pools or have been around them your whole life, at some point you’ve probably wondered to yourself what is a pool skimmer?  You know there is an opening on the side of the pool. Furthermore, there’s a basket inside that opening that you clean out from time to time. 

You also know that sometimes you get mice and insects in the skimmer, along with a bunch of leaves and pine needles depending on where you live.  If you live in the southwest you probably know to tap the skimmer lid before opening just in case you have a rattle snake curled up inside.  There is all sorts of practical skimmer related knowledge, but what is a pool skimmer exactly?

What Is A Pool Skimmer?

First let’s start with the goal of the skimmer, and why it’s in the pool to begin with.  A pool skimmer’s intention is to pull in anything that lands on the pool surface but doesn’t sink to the bottom.  This includes leaves, pine needles, pollen, bugs, small sticks, and so on.  Imagine the surface of the swimming pool is a tablecloth on a table.  The skimmer is pulling the tablecloth off the table, and bringing everything on the tablecloth with it.  So how does the skimmer do it?

How Does A Pool Skimmer Work?

The trick to an effective skimmer is the weir depth and by association the weir length.  So what is the weir?  Most skimmers have a ‘flappy door’ in the area between the basket and the pool which we call the skimmer’s ‘throat’.  This is the door that makes noise when you jump into the pool, or dive off the diving board.  In the swimming pool world, we call this door the ‘skimmer weir’. 

The skimmer weir has buoyancy, and is always trying to float to the top, and close off the skimmer from the pool, and does so when the pump turns off.  However, the suction from the pool pump is pulling water over the weir and forcing the weir to be slightly below water level.  This causes a thin layer of water to be pulled over the skimmer weir and into the skimmer.  

what is a pool skimmer job

What Is A Pool Skimmer Normal Mode Of Operations?

The effective ‘pulling’ zone of a skimmer, that is the area where debris can be reliably pulled into a skimmer is described as a skimmer’s ‘reach’ into the pool.  When designing a pool, and determining flow rates for skimmers, you want to maximize a skimmer’s reach.  This means you need enough flow to pull the weir door down, but not too much flow.  There’s a sweet spot and if you look at the manufacturer’s literature for the skimmer you’ll find the ideal flow rate shown for your specific skimmer.

Alternative Pool Skimmer Types

Some alternative skimmer types exist which improve on the typical skimmer design in various ways.  

Circular Weir Pool Skimmer

One alternative design is the circular weir skimmer.  This type of skimmer does not have the ‘flappy door’ style skimmer weir and instead has a rigid floating basket.  As the pump turns on and water is drawn through the skimmer, the basket is pulled slightly underwater, and the perimeter of the skimmer basket becomes the skimmer weir. 

These types of skimmers are referred to as ‘circular weir’ skimmers. Unfortunately, they are not very popular.  However, they are one of the easiest skimmers to service. Additionally, you never have a broken weir door from too much diving into the pool.  Some skimmers like the Pentair Admiral have the option of either standard flappy door weir, or a circular weir.

Venturi Pool Skimmer

Another skimmer type which is designed to increase the reach of the skimmer measurably is the venturi skimmer. A good venturi skimmer product is the Pentair Quickskim.  These skimmers are designed to work with suction from the pump and / or pressure from the return line from the pump.  Below the skimmer basket on the back of the skimmer there is an attachment for a return line from the pump.  This return line will be a reduced to a small opening, 1/2” or so, and opposite this opening will be a 2” pipe returning through the wall of the pool. 

What is a pool skimmer venturi style

High pressure water comes in under the skimmer. The water then pushes out into the pool below the skimmer throat.  This causes water to be drawn over the skimmer weir from the pool without the need for any suction.  This allows you to use both suction and return water to clean the surface of the pool.

There are numerous other options for skimmers. Some of these include ABS plastic versus PVC, different colors, consisting usually of black, white, or gray, and many more options.  

What Is A Pool Skimmer Summary?

Ultimately, what is a pool skimmer?  A pool skimmer is the workhorse of pool cleaning.  If your skimmers are operating well, your pool is staying clean. Problems occur when skimmers are clogged or the valves are turned off. When there’s no skimming going on, your pool is dirty.  You want your pool cleaner to be a supplement to the skimmers. Always make sure your skimmers are clean and operating.