Fan Curve
What does the fan curve actually tell a machinist?
At a fixed fan design and speed, it shows the relationship between flow rate, static pressure, and often power; as pressure rises, airflow typically falls.
How is the fan curve used to size dust collection in a CNC or millwork shop?
Determine the required CFM at each pickup point, estimate total static pressure from ducts, fittings, separators, and filters, then choose the fan whose curve intersects that duty point with acceptable BHP margin.
Why does airflow drop after filters load up?
Loaded filters increase static pressure, moving the operating point left on the curve, which reduces delivered airflow unless fan speed or system design is changed.
A fan curve is a performance graph for a specific fan showing how airflow (CFM) changes with static pressure, and often brake horsepower, at a given fan speed. It comes from manufacturer test data and is central to selecting and diagnosing dust collection, make-up air, and extraction systems in CNC and millwork shops.
In a CNC cell, millwork shop, or edgebanding line, the fan curve is used to size and verify dust-collection blowers, make-up air fans, downdraft tables, and cabinet extraction systems. The operating point is found where the system curve intersects the fan curve; that intersection determines actual airflow and power required at that resistance. A fan that moves enough air in free air can underperform once duct losses, blast gates, cartridge filters, or flexible hose are added. Sanding dust, MDF fines, chip load, and edge-trim residue all create varying static pressure. If the fan is selected only by nominal CFM, extraction at the machine hood can collapse when multiple lines open or filters load up. Shops use the curve to match motor size, verify BHP at the target duty point, and avoid operating outside the efficient region where airflow drops sharply as resistance increases.
Weak hood capture: A blower may meet its catalog CFM rating in free air but fail on the floor once duct elbows, separators, filters, and flex hose raise static pressure. Dust escapes at saws or sanders, and downstream filters overload.
Motor overload trips: Selecting a higher-speed or higher-pressure fan without checking the horsepower curve can overload the motor at the real operating point. This causes breaker trips, overheating, or premature bearing and belt failure.
Inaccurate airflow estimates: If RPM, impeller diameter, blade pitch, or the number of open branches in a duct network changes, the fan’s operating point changes. Using the wrong curve leads to poor commissioning results.