Pool Anatomy

Pool circulation is often compared to a living organism’s vascular system. It’s a tempting comparison because they both are mainly composed of a pump, piping network and the function is to the delivery of clean fluid and removal of waste. There are even comparisons with organs in the body such as the heart, kidneys and liver. Without taking the biological metaphor too far, here is a description of pool anatomy:


Several types of pumps exist. Each type has its strengths and weaknesses. Centrifugal pumps are the type used in pool systems as well as most water features. Centrifugal pumps work by accepting water into a centrifuge through an inlet and accelerating water in a circular pattern with a spinning impeller powered by a motor. The impeller then directs the water out through a discharge port connected to the piping system. They also produce high flow rates. Each pump performs based on its design and size. Pump manufacturers provide performance information in the form of pump curves. These curves are a graphic chart that tracks the pumps performance output in GPM for a given TDH. Now you see why TDH is necessary. Pumps are designed to function within certain ranges of TDH. We need to know it so we can size the pump correctly.


The filter’s job is to remove impurities from the water. It does that by straining the water through one of a number of kinds of media. Any particle larger than the gaps in the straining medium will not pass through and will be removed from the system. 


The heater’s function is to add heat energy to the water to raise the temperature of the water for the comfort of bathers. There are different types of heaters and each is best employed to different conditions and preferences but the end result is the same. Warm water.

Water Treatment

As with filters and heaters, there are several water treatment technologies to choose from. But the purpose is the same. Filtering the water is not enough to eliminate impurities. Some are microscopic bacteria, dissolved solids, chemicals that upset the chemical balance etc. Water treatment introduces a sanitizer such as Chlorine to eliminate bacteria, and acidic compounds to re balance water chemistry. Many smart systems do this automatically with sensors and controllers. Some work by adding a set dosage to the water regularly. Some pools (probably most) do not have treatment systems. The sanitization and chemistry maintenance is done manually either by the owner or by a maintenance person.

Return / Inlet Fittings

Return fittings are the interfaces between the pipe and the inside of the pool. They are cast into the wall or floor and are designed to safely direct or dissipate fresh clean water into the pool. directional eyeball and adjustable floor returns are the two standard fittings. Directionals may be aimed in oblique directions within a limited angle. They are usually placed in the wall and project water out into the pool. Adjustable floor returns are placed in the floor and discharge water in a near horizontal 360 degree pattern. They have higher flow ratings but discharge water at lower velocities than directionals at the same flow rate.


The Skimmer is a kind of drain. It is installed at water level so that it can draw water from the surface of the pool. It is the main means of cleaning the water surface where up to 80% of impurities are concentrated.  You will require at least one skimmer per 800 square feet of pool surface area. Skimmers are designed to draw water from the surface of the pool where up to 80% of impurities are found. From body oils to dirt and debris.

Vacuum Lock

The Vacuum lock or vac lock fitting is essentially a stopper that plugs a pipe opening in the pool wall below the water line that is connected to the suction side of the piping system. It is used for vacuum cleaning the floor of the pool by unplugging it and connecting it to a hose with a cleaning nozzle at the end. It picks up debris and sends it through the circulation system where it is captured in the filter.

Main Drain / Inlet

The main drain is the primary point of water exit from the pool.  They usually handle higher flow than the skimmers and they remove water from the depths of the pool along with debris that has sunk to the bottom and cooler water that might otherwise sit and suffer from poor circulation. 

Overflow Drain

The overflow drain’s purpose is to direct excess or displaced water – usually from a rain storm or heavy bather displacement – into the site drainage system rather than having it overflow onto the adjacent deck.

Auto Refill System

The pool will lose water to evaporation and heavy use from time to time. The refilling process is automated with a water level sensor and a refill line into the pool, above water level. There is a controller that sends a signal to solenoid to open a valve allowing potable water to enter the pool topping it up until the sensor is satisfied.


Last but not least, the pool. More than just the sum of the parts mentioned above, the vessel containing clean, sparkling, dancing gurgling water is the reason for all the other bits. The pool’s architectural design has a direct impact on how it’s used and enjoyed. Architecture is beyond the scope of this document but the water contained is still of concern to us. It’s circulation within the vessel of utmost importance. the location and number of fittings is critical for performance and safety.

Piping System

Consisting of pipes, fittings and valves the piping system is what connects all of the above. Most residential swimming pool pipes are made of polyvinyl chloride (PVC). PVC is manufactured in two standards, they are the more common schedule 40 (SCH 40) and schedule 80 (SCH 80). SCH 40 has a slightly thinner wall than SCH 80 and so has a slightly larger interior diameter. That is significant because the larger size affects flow rate and line velocity. Fittings are used to connect pipe segments when it needs to change direction or split into two or more branches, increase or decrease in size. Most pool piping systems will have control valves and sometimes diverter valves or check valves. Control valves regulate the flow of water through the pipes and diverter valves also known as three way valves control the direction of flow through a 3 way branch. Check valves allow water to flow in one direction only and will stop flow if the direction of flow begins to reverse.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s