Pump Curve
What is the operating point?
The point where the pump curve intersects the system curve; it is the actual flow and head the installed system will run at.
Why does impeller trim matter?
Smaller impeller diameters reduce head, flow, and power; pump curves often include multiple impeller trims so the same pump body can be matched to different duty points.
What does the efficiency curve tell you?
It shows where hydraulic efficiency is highest, which is usually the preferred region for stable, economical operation.
A pump curve is a graphical performance map for a specific pump model showing how flow changes with head or pressure at a given speed, often including efficiency, power, and NPSH data. In practice, it defines the pump's operating envelope and the actual operating point where the pump curve intersects the system curve.
On a CNC cell, millwork line, or coolant/filtration skid, the pump curve is used to size and verify pumps for coolant circulation, vacuum hold-down, chip conveyance, washdown, adhesive transfer, and other fluid systems. The core engineering check is whether the pump meets the demanded flow rate at the actual total dynamic head (TDH) from plumbing, valves, fittings, filters, and elevation changes. In CNC vacuum applications, the curve is critical because the pump's vacuum level depends on its characteristic curve and the system's leakage and restriction, which determine the real operating point. Pump curves are read with flow on the x-axis and head on the y-axis, while additional curves show efficiency, horsepower, and NPSHR. Manufacturer curves often follow standardized test tolerances, such as ISO 9906:2012 Grade 3.
Selecting by flow only: A pump may move the target GPM on paper but fail once real system head is added, causing undersupply, poor coolant delivery, or weak vacuum hold-down.
Ignoring NPSH/NPSHR: If the available suction head is too low, the pump can cavitate, causing noise, vibration, flow instability, and accelerated impeller damage.
Running far from the best efficiency point (BEP): Operating too far left or right of the efficiency peak increases heat, power draw, vibration, and seal/bearing wear, common on continuously running coolant pumps.