Step 1: Identify potential causes for a pump failing to deliver water.
- A. Lack of Priming: Centrifugal pumps cannot operate with air. Priming involves filling the pump and suction line with water to expel air before operation. This is a frequent cause of water delivery failure and is a valid reason.
- B. Improper Lubrication: Inadequate lubrication degrades bearings, leading to overheating, excessive wear, and eventual mechanical pump failure. However, this issue does not immediately prevent water delivery unless the bearings have already seized. It causes mechanical, not hydraulic, failure.
- C. Excessive Pumping Head: Each pump has a maximum head capacity (shutoff head at zero flow). If the system's static head exceeds this limit, the pump cannot generate enough pressure to move water. This is a valid cause.
- D. Clogged Suction Pipe: A blockage in the suction pipe or foot valve prevents water from entering the pump, thus stopping water delivery. This is a valid cause.
Step 2: Determine the correct combination of causes.
The direct hydraulic factors preventing a pump from delivering water are A, C, and D. Factor B pertains to mechanical maintenance and long-term operational issues. Consequently, A, C, and D represent the correct combination of common causes.