Question

If a centrifugal pump does not deliver the water, the possible causes are:
A. Priming is not done.
B. Lubrication is incorrect.
C. Pumping head is too high.
D. Suction pipe is clogged.
Choose the correct answer from the options given below:

• A. A, B and C only
• B. B, C and D only
• C. A, B and D only
• D. A, C and D only

Hint:

For pump troubleshooting (no delivery), think about the water's path and the pump's function. 1. Can water get in? (Check for clogged suction, air leaks, is it primed?) 2. Can the pump move it? (Is it rotating in the right direction? Is the impeller damaged?) 3. Can it overcome the system's resistance? (Is the head too high? Is a valve closed?)

Answer 1

The Correct Option is D

Step 1: Analyze each potential cause for a pump's failure to deliver water.
- A. Priming is not done: A centrifugal pump cannot pump air. Priming is the process of filling the pump casing and suction line with water to remove air before starting. Lack of priming is a very common reason for failure to deliver water. This is a valid cause.
- B. Lubrication is incorrect: Incorrect lubrication affects the bearings, which can lead to overheating, excessive wear, and eventual mechanical failure of the pump. However, it does not directly prevent the pump from delivering water initially, unless the bearings have already seized. It's a cause of mechanical failure, not hydraulic failure.
- C. Pumping head is too high: Every pump has a maximum head it can generate (the shutoff head, at zero flow). If the actual static head of the system is higher than this, the pump cannot overcome it and will not deliver any water. This is a valid cause.
- D. Suction pipe is clogged: If the suction pipe or its foot valve is blocked, water cannot enter the pump, and therefore it cannot be delivered. This is a valid cause.
Step 2: Conclude the correct combination.
The direct hydraulic reasons for a pump not delivering water are A, C, and D. Statement B relates to mechanical maintenance and long-term failure. Therefore, A, C, and D is the correct combination of common causes.