It requires 151 HP to operate a centrifugal pump having a 14.75 inch impeller at 1800 RPM, at a capacity of 2250 GPM with a 218 foot head. If during an overhaul of the pump, the impeller diameter is reduced to 14 inches, the discharge head of the pump operating at the same RPM would be __________.
• Pump affinity laws for centrifugal pumps (relationship between impeller diameter, head, and horsepower at constant RPM) • How head (H) changes when impeller diameter (D) changes but speed (RPM) stays the same • The ratio method: using the square of the diameter ratio to estimate new head
• What law relates the change in pump head to the change in impeller diameter when the pump speed remains constant? • How can you use the ratio of the new impeller diameter to the old diameter to predict the new head, without recalculating from horsepower? • After you find the new theoretical head from the diameter ratio, which option is numerically closest to your calculated value?
• Confirm that for a centrifugal pump at constant RPM, head is proportional to the square of the impeller diameter (H ∝ D²) • Set up the ratio correctly: H₂ / H₁ = (D₂ / D₁)² using the given diameters in inches • Be careful with the arithmetic of squaring the diameter ratio and then multiplying by the original 218 ft of head
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