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Hydraulics: Learning to go with the flow

By Marcelle Dibrell

Over the course of their careers, there are two topics that the majority of veteran service professionals tend to become truly proficient in: water chemistry and hydraulics. Understanding water chemistry is essential for maintaining water quality but the circulation and filtration system is just as important. 

Without both proper chemistry and circulation, the water just isn’t clean, and cleaning the pool water is what service technicians have been hired to do. The pump is frequently called the heart of the circulation system because it performs the task of any biological heart: sending and receiving fluids to and from all of the system’s extremities. 

Just as the human heart sets the circulation system in motion, the pump creates water flow. Most pumps are centrifugal pumps and they give energy to the water in the form of pressure and velocity. Water is drawn into the pump to the impeller and thrown out of the spinning impeller to the filter by centrifugal force. 

And if the pump is the heart of the circulation system, the filter is the system’s liver and kidneys, removing pollutants and impurities to prevent the buildup of wastes. But just as a biological heart is not one-size-fits-all, neither is a pool pump, and the entire system must be optimized to overcome resistance and achieve the required flow and turnover rates. That means careful consideration of the size of the pump, based on the specifics of the plumbing. It can be understood through study of a science called hydraulics.

In the pool and spa world, hydraulics has to do with the pump’s ability to overcome the total dynamic head. For the circulation system to operate, the pressure head of the pump must be greater than the total resistance head of the system. But it is not enough that the pressure head be greater than the resistance head. In reality, the pressure must be great enough to produce the desired flow rate. It is essential to determine the desired flow rate so that the proper turnover rate can be achieved. 

Furthermore, for the water to achieve the desired clarity, a large portion of it must pass through the filter, and that is determined by the number of times that it passes through the filter, or the number of turnovers. This relates to the amount of time that the filter should be run. For this issue of Service Industry News, we focus on the heart of the circulation process — the pump — and the means by which it redistributes the water to every corner of the pool, through a process called hydraulics.

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