What percentage of rated head is the maximum allowed for a pump shut-off?

• A. 150%
• B. 130%
• C. 120%
• D. 140%

Answer: (D)

When a pump is tested or run with almost no flow, the head it produces is called the shut-off head. The pump’s rated head is the head it’s designed to develop at its rated flow. There’s a safety limit for how high the shut-off head can be relative to the rated head, to protect the motor, bearings, and piping from excessive stress in a no-flow condition. That limit is 140% of the rated head, so the maximum allowed shut-off head is 140% of what the pump is rated to deliver. Going higher than that could indicate or cause equipment problems and isn’t permitted. The other percentages are either below the allowed maximum or exceed it, which is why 140% is the correct upper bound.