What does 'rated head' or 'rated capacity' refer to on a pump?

• A. The maximum head the system can withstand without damage.
• B. The actual head during peak demand testing.
• C. The manufacturer-specified performance at designed operating conditions.
• D. The head when the pump operates at zero flow.

Answer: (C)

In pump terms, rated head or rated capacity is the manufacturer’s guaranteed performance at the design point. It means the head (or flow) the pump is specified to produce when it runs at the rated speed with the intended fluid and suction conditions, i.e., the design point shown on the pump curve. This value is used to confirm the pump will meet the fire protection system’s expected demand under normal operating conditions. It isn’t the maximum head the system can tolerate, nor the actual head you’d see during peak-demand testing (that varies with system loading), nor the head at zero flow (that’s the shutoff head).