Question

Given below are two statements:
Statement (I): Shaft horse power is always less than water horse power.
Statement (II): For direct driven pump, shaft horse power is equal to brake horse power.
In light of the above statements, choose the most appropriate answer from the options given below.

• A. Both Statement (I) and Statement (II) are true.
• B. Both Statement (I) and Statement (II) are false.
• C. Statement (I) is true but Statement (II) is false.
• D. Statement (I) is false but Statement (II) is true.

Hint:

Power sequence in pumping systems:
\[ \text{Brake Horsepower (BHP)} \ge \text{Shaft Horsepower (SHP)} > \text{Water Horsepower (WHP)} \] - BHP = SHP for direct-driven pumps.
- SHP is always greater than WHP due to pump losses.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
When pumping water, energy is transferred from a power source (like an electric motor or engine) to the pump shaft, and then to the water.
During this transfer, mechanical and hydraulic losses occur, which are represented by different horsepower terms.

Step 2: Detailed Explanation:
Let us analyze each statement individually:
- Statement (I) is false:
- Shaft Horsepower (shp): The power delivered by the motor/engine to the pump shaft.
- Water Horsepower (whp): The actual power delivered to the water, which represents the useful work done in lifting the water.
Due to mechanical friction, disk friction, and hydraulic turbulence inside the pump, some energy is always lost as heat.
Therefore, the pump efficiency (\(\eta_p\)) is always less than \(100\%\):
\[ \eta_p = \frac{\text{Water Horsepower (whp)}}{\text{Shaft Horsepower (shp)}} < 1.0 \] This means that Shaft Horsepower must always be greater than Water Horsepower (\(shp > whp\)).
Thus, Statement I is false.
- Statement (II) is true:
- Brake Horsepower (bhp): The power output of the engine or motor.
In a direct-driven pump, the motor shaft is coupled directly to the pump shaft without any intermediate belt, chain, or gear drives.
Because there are no transmission losses, the power output of the motor (bhp) is completely transmitted to the pump shaft (shp).
Thus, \(shp = bhp\).
Therefore, Statement I is false, but Statement II is true.

Step 3: Final Answer:
Statement (I) is false but Statement (II) is true.