I was curious if there was a practical way to reduce the flow rate of my pump without damage to the pump. So I asked the folks that make my pump (PerformancePro Artesian 2 speed). Here is their response:
“Hello thank you for choosing PerformancePro Pumps and for your inquiry. I suggest you simply install a ball valve on your discharge pipe at a location convenient to your purpose. Closing the valve only creates artificial head. The pump is doing less work with less water weight work being done. All PerformancePro Pumps are designed to operate at any point along their performance curve as long as a few gallons per minute flow is maintained to cool the pump.”
So I found the performance curve for my pump. I will have to simulate 10-15 feet of head to reduce it down to 1800-2400 GPH at the lower RPMs. At higher RPMs that level of head has no impact on performance. So I get the best of both speeds without fiddling with the valve. This will give me slower flow for better filtration and hopefully less evaporation loss at the falls. My pump is the gold line on the chart below. The area in Pink is what I am aiming for.