Question

Shaft horse power is always

• A. Equal to pump efficiency
• B. Greater than water horse power
• C. Lesser than water horse power
• D. Equal to water horse power

Hint:

Power hierarchy in pumping: $\text{Input Electrical Power} > \text{BHP} > \text{SHP} > \text{WHP}$. Therefore, $\text{SHP} > \text{WHP}$ always.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Energy dissipation due to mechanical, hydraulic, and disc friction inside a centrifugal pump dictates that input mechanical shaft power always exceeds hydraulic output water power.
Key Formula or Approach:
\[ \eta_{\text{pump}} = \frac{\text{Water Horse Power (WHP)}}{\text{Shaft Horse Power (SHP)}} \text{WHP} \]

Step 2: Detailed Explanation:
In pump mechanics:
1. Water Horse Power (WHP): The useful hydraulic power delivered to the pumped fluid:
\[ \text{WHP} = \frac{\rho g Q H}{75} \text{ (or } \frac{Q H}{75}\text{)} \]
2. Shaft Horse Power (SHP): The mechanical brake power supplied to the rotating pump shaft.
Because real pumps suffer internal hydraulic friction, casing shock losses, and bearing/packing gland mechanical friction:
Pump efficiency is always less than 100% (\(\eta_p < 1.0\)).
Therefore:
\[ \text{SHP} = \frac{\text{WHP}}{\eta_p} > \text{WHP} \]

Step 3: Final Answer:
Hence, Shaft horse power is always Greater than water horse power, corresponding to option (B).