System Curve Analysis

Both impeller trimming and variable frequency drives can cut pump energy, but they solve different problems. If you treat them as interchangeable, you can end up with a "savings" project that either fails to meet process needs or carries unnecessary life cycle cost. The fastest way to stay out of trouble is to apply the Golden Rule: trimming is for constant excess head from an oversized pump, while speed control is for variable demand where your system curve shifts over time. That single line will...

If you are deciding between pumps in series vs parallel, you are really deciding what you want the station to do when the process changes: build more head, pass more flow, ride out a pump outage, or hold efficiency near BEP across a wide operating band. The right answer shows up when you put the combined curves on the same plot as your system curve, then pressure check the suction limits, controls, and failure modes you will actually see on site.

Practical selection rules and pitfalls: a quick decision...