Question

The pump's efficiency is at its peak when the specific speed values range from

• A. 100-450
• B. 500-950
• C. 1000-1950
• D. 2000-3000

Hint:

Peak centrifugal pump efficiency zone: $N_s = 2000 - 3000$ (US units) $40 - 60$ (Metric SI units).

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Centrifugal pump efficiency reaches its global hydrodynamic maximum at optimal impeller proportions where disc friction losses, shock losses, and passage friction are minimized.
Key Formula or Approach:
\[ N_s (\text{US gpm}) = \frac{N (\text{rpm}) \sqrt{Q (\text{gpm})}}{[H (\text{ft})]^{3/4}} \]

Step 2: Detailed Explanation:
Hydraulic pump design characteristics show that:
- At very low specific speeds ($N_s < 1000$), large diameter impellers with narrow passages suffer high rotational disc friction and narrow passage boundary drag.
- At very high specific speeds ($N_s > 6000$), axial passage diffusion losses and blade incidence losses reduce efficiency.
- Peak maximum hydraulic efficiency (frequently reaching 88--92%) occurs consistently in the optimal specific speed range of 2000 to 3000 (US engineering units) or 40 to 60 (metric SI units).

Step 3: Final Answer:
Therefore, the pump efficiency peaks in the specific speed range of 2000-3000, corresponding to option (D).