A six-stage centrifugal pump delivers 120 L s⁻¹ against a total head of 510 m. If the design speed of this pump is 1450 rpm, the specific speed of the pump will be __________.
Official Answer Key:
565 to 570
Step-by-Step Solution & Explanation
• For multistage pumps, specific speed is computed using the head developed per stage: Hstage = Htotal/no. of stages = 510/6 = 85 m.
• Metric specific speed: Ns = N√Q / H^0.75, with N in rpm, Q in L/s (this pump-industry convention), H in m.
• Ns = 1450 × √120 / (85)^0.75 = 1450 × 10.954 / 27.99 = 15,883/27.99 ≈ 567, inside the accepted range 565–570.
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