What is a Pool Weir and How Does it Work With a Skimmer?

How Your Pool's Plumbing System Works

pool weir
Pentair swimming pool weir replacement. Amazon.com

A weir is a type of barrier across a river that is created to adjust or alter its flow. With this in mind, a weir for a swimming pool is a barrier in a skimmer over which water flows. A floating weir raises and lowers its level to match the water level in a pool or spa. Another type is shaped like a barrel and floats up and down inside the skimmer basket. 

Understanding a Pool's Basic Plumbing System

To help you troubleshoot any problems that might arise with your swimming pool, it helps to have a basic understanding of how your pool works.

In this case, it's the pool's plumbing system. Water enters a pool through a main drain, a skimmer, or both. It journies to a three-port valve and into the pump, which is run by an attached motor. From there, the water travels through a filter, then up to solar panels or to the heater (if they are installed) and back through the valves to the pool return lines.

Enter the Skimmer

This is where the skimmer comes in. Some pools have more than one. A skimmer's primary function is to pull water into the system with a skimming action, which means it pulls in dirt, oil, leaves, twigs, and debris hopefully before they can fall to the bottom of the pool. A skimmer also provides a conveniently located suction line for vacuuming.

Many pool circulating systems have at least two surface skimmers connected to the pump. While most skimmers are built into the pool, some types are designed to hang on the side.

Most are molded, one-piece plastic units. Older pools often have built-in-place concrete skimmers. For the most effective collection of debris, there should be one skimmer for approximately every 500 square feet of pool surface.

Newer models include floating automatic or robotic skimmers, some of which are solar powered.

This kind of skimmer connects to an automatic pool cleaner (vacuum), while the solar model floats independently along the surface of the pool, collecting all types of debris. Both models are designed to keep a pool cleaner, cut down on your time and energy spent maintaining the pool, and save money and energy by not putting so much strain on the pump.

The Skimmer and the Weir

Most skimmers consist of a tank with a projecting throat-like device on its upper side. There, a self-adjusting weir (or floating weir) performs the skimming action by regulating the amount of water that enters the skimmer. Because it adjusts to allow only a thin sheet of water to spill over, velocity, not volume, is the key to good skimming action. It must have an equalizer line--a pipe that extends from the bottom of the skimmer about 12 to 18 inches through the pool wall into the water--to prevent air from being sucked into the system when the water level is low. Skimmers work best when located on the "down wind" side of the pool; the wind helps push debris toward its opening.

Water pours over a floating weir that allows debris to enter. When the pump is shut off and the suction stops, the weir floats into a vertical position, which prevents debris from floating back into the pool.

Some skimmers don't have this type of weir and use a floating barrel as part of the skimmer basket. The basket collects leaves and larger pieces of debris, allowing you to remove them easily. 

Replacing a Weir

Luckily, a weir is a fairly easy part to replace. With a pair of pliers, remove the old or damaged weir from the skimmer and insert the replacement in the same position by pulling out its pins. A spring should release retaining rods that push against the skimmer walls. Popular brands include: