Question

When there is direct drive from the engine or electric motor to the pump, then at what drive efficiency the brake horse power is equal to shaft horse power

• A. 25%
• B. 50%
• C. 75%
• D. 100%

Hint:

Direct drive with zero transmission slip/friction $\implies \eta_{\text{drive}} = 100\% \implies \text{BHP} = \text{SHP}$. Belt drive $\implies \eta_{\text{drive}} \approx 90-95\%$.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Power transmission efficiency connects engine brake horsepower (BHP) to pump shaft horsepower (SHP).
Key Formula or Approach:
\[ \text{SHP} = \text{BHP} \times \eta_{\text{drive}} \implies \text{BHP} = \frac{\text{SHP}}{\eta_{\text{drive}}} \]

Step 2: Detailed Explanation:
For a directly coupled pump (where the electric motor shaft is connected directly to the pump shaft via a rigid or flexible coupling without intermediate belt, pulley, or gearbox reductions):
If drive transmission efficiency is 100% (\(\eta_{\text{drive}} = 1.0\)):
\[ \text{SHP} = \text{BHP} \times 1.0 = \text{BHP} \]
Thus, brake horsepower equals shaft horsepower when drive efficiency is 100%.

Step 3: Final Answer:
Therefore, the drive efficiency is 100%, matching option (D).