A pump doesn't get to choose its own flow rate — the pipeline it's connected to chooses for it. Every pump will settle at exactly the one flow where the head it produces matches the head the system demands, called the operating point, and finding that point is one of the most practical skills a top-tier operator uses when troubleshooting underperforming pumps or evaluating a new pump purchase. This guide covers that intersection method, then applies pressure/head calculations to multi-zone and multi-story real-world design problems.
The System Head Curve
At the previous tier you learned to calculate Total Dynamic Head for one specific flow rate. But TDH isn't a fixed number — it changes with flow, because friction loss and velocity head both grow as flow increases (friction loss grows roughly with Q1.852 under Hazen-Williams). Plotting TDH against a range of flows produces the