What does the pump head vs flow rate curve represent, and how is it used in system design?

• A. It shows the head pumped at different discharge rates; the operating point is where pump curve intersects system curve
• B. It shows efficiency vs flow
• C. It shows friction factor vs flow
• D. It shows discharge vs pressure

Answer: (A)

The pump head vs flow rate curve shows how the head (pressure rise) the pump can develop changes as you vary the discharge rate. For many pumps, head is high at low flow and decreases as flow increases, reflecting how the pump’s capability shifts with operating conditions.

In system design you compare this pump curve to the system head curve, which represents the head the piping network requires to push the fluid through at different flow rates (friction losses, pipe size, elevation, valves, etc.). The system curve typically rises with increasing flow because more head is needed to overcome friction at higher velocities.

The operating point is where the two curves intersect. At that point, the pump’s head exactly matches the system’s head requirement, giving the actual flow and head the system will experience. This intersection is used to select a pump that will meet the desired flow without over- or under-delivering head. If the intersection isn’t satisfactory, you adjust the design by changing the pump selection or altering the system (larger pipes, fewer restrictions, etc.) to shift the curves toward the desired operating point.