CPM Plant Equipment Maintenance & Troubleshooting 2

Question 1

A centrifugal pump makes a crackling, gravel-like noise and its discharge pressure fluctuates. What is the most likely cause?

Accepted Answer

Cavitation from insufficient NPSH available

Answer

Cavitation occurs when vapor bubbles form and collapse because NPSH available falls below NPSH required, producing gravel-like noise and unstable pressure.

Question 2

Which action would most directly increase NPSH available to a centrifugal pump?

Accepted Answer

Raising the liquid level in the suction tank

Answer

Raising the suction liquid level increases static head on the suction side, which increases NPSH available.

Question 3

A new mechanical seal leaks steadily right after installation. Which is the most likely cause?

Accepted Answer

Seal faces were damaged or contaminated during installation

Answer

Immediate leakage on a new mechanical seal usually means chipped, scratched, or dirty faces, or a damaged O-ring from installation.

Question 4

Why should packing on a centrifugal pump be allowed to leak slightly during operation?

Accepted Answer

To lubricate and cool the packing and shaft sleeve

Answer

A small controlled leakage lubricates and cools the packing, preventing it from burning and scoring the shaft sleeve.

Question 5

A centrifugal pump runs but delivers no flow after a rebuild. Which should be checked first?

Accepted Answer

Whether the pump is primed and rotating in the correct direction

Answer

Loss of prime and reversed rotation are the most common reasons a rebuilt centrifugal pump produces no flow.

CPM - Certified Plant Mechanic Practice Test

CPM - Certified Plant Mechanic Practice Test

CPM Plant Equipment Maintenance & Troubleshooting 2