If your goal is to run your pump at a specific SPEED (RPM), then VS is the way to go. If your goal is to run at a specific FLOW (GPM), then a VF pump is the way to go. I have both but the VF pump is my main pump and I have no complaints. What I like about the VF pump is that you program to flow at the gallons per minute you need and the pump will make sure that happens. To me, it's the best of both worlds - running at the lowest RPM necessary to achieve GPM desired saves on the electric bill and running at a higher RPM that is necessary to meet the GPM need while overcoming any issues that may hinder the flow rate needed.
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