When finished the valve needs to be in this position






Pool Drain Systems

We've already seen that the water in a swimming pool needs to circulate through a filtering system, to remove dirt and debris. During normal operation, water flows to the filtering system through two drains at the bottom of the pool and a skimmer drains around the top of the pool.

Diagram of a swimming pool system

The main drains are usually located on the lowest point in the pool, so the entire pool surface slants toward them. Most of the dirt and debris that sinks exits the pool through these drains. To keep people from getting their hair or limbs caught in the plumbing, the drains are almost always covered with grates or antivortex covers (a cover that diverts the flow of water to prevent a dangerous vortex from forming).

The skimmers draw water the same way as the main drains, but they suck only from the very top of the pool (the top eighth of an inch, typically). Any debris that floats -- leaves, suntan oil, hair -- leaves the pool through these drains. The diagram below shows a common system.


Diagram of a swimming pool skimmer


Swimming pool return port
The return port


Most swimming pools also have a couple of vacuum ports, which are only used in pool cleaning. These ports attach to pool vacuum cleaners, which work something like ordinary vacuum cleaners except that they suck water instead of air. The vacuum ports may have their own pumping system, but in most pools they are driven by the main pump.


Swimming pool vacuum cleaner
A pool vacuum cleaner


After making its way into the various drains, the water flows on to the filtering stage. In the next section, we'll find out what the pumping and filtering systems are all about.