Pool circulation is critical if you want to maintain that perfect “dive right in” crystal blue water. Proper pool water circulation helps distribute chemicals evenly, so no matter how hard you try to keep your pool chemistry balanced, you will still run into problems if the water isn’t circulating properly.
Below you will find a quick lesson in proper pool water circulation:
How a Pump Works:
Swimming pool water must travel through an elaborate piping system and filter to remain clean. As it moves, it generates friction. If parts of the system are higher than others, then a force is required to raise the water. Pumps harness the power of a motor to overcome friction and gravity in pool systems, leaving you with clean filtered water.
Most circulating pumps are centrifugal. A disc-like piece called an impeller rotates on a shaft inside the main house. As the impeller spins, it provides velocity to the water inside the pump casing, causing the water to move from the center of the impeller toward the edges, forcing the water through piping and filters.
Every centrifugal pump has a maximum pressure it must develop to operate.
How to Size Pumps:
Centrifugal pumps are rated in feet or meters of head. Meters of head is the height to which the pump can push water straight up against the force of gravity. They are also rated for flow in gallons per minute (gpm) possible for a specified head. This is determined by the size of the pump and the power available from the motor.
The pipe and equipment between the pump discharge and the pool has a known resistance. This resistance can be determined by using the pipe size, length and type of fittings. Gravity is also a known quantity, which allows us to calculate the pressure required to overcome force.
The total of all these resistances is called the total dynamic discharge head. It is referred to as dynamic because it occurs while the water is moving. The gravity portion alone would be termed static discharge head because it is constant; occurring whether or not the water is moving. These “heads” are expressed in pounds per square inch (psi) or feet, or meters of water.
For example, a column of water one inch and 2.31 ft. high weighs one pound. The correlation between psi and feet of water is therefore 2.31 ft. of water per psi.
How Pumps Move Water:
The impeller spins and the water moves from the center, or eye, toward the edges, creating a vacuum. Water then flows by suction pressure. The suction pressure available to a pump is provided by atmospheric pressure (the weight of all air pushing down on the water) and gravity. These forces push the water through the system until it reaches the impeller eye.
The moving water generates friction in the pipes and uses that pressure. If that system friction consumes too much of the available atmospheric pressure, the water vaporizes or cavitation occurs. Both of these will damage the pump.
Find out more about pool gutters and perimeter systems, and contact us with any questions about your pool construction or renovation project.
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