What does the system curve illustrate, and how is it used with a pump curve to select an appropriate pump?

• A. The system curve shows pump efficiency as a function of head.
• B. The system curve shows velocity head as a function of discharge.
• C. The system curve shows head loss as a function of discharge; its intersection with a pump curve yields the operating point.
• D. The system curve shows pipe diameter as a function of discharge.

Answer: (C)

The system curve represents the head required by the piping system as discharge changes, which mainly comes from friction losses plus any static head. When selecting a pump, you plot this system curve and overlay the pump’s head-capacity curve. The operating point is where the two curves intersect—the discharge and head at which the pump can overcome the system’s resistance. This intersection tells you the actual flow the system will receive and the head the pump must provide. The other ideas aren’t correct because the system curve isn’t about pump efficiency, velocity head, or pipe diameter; it specifically tracks head loss (plus static head) versus discharge.