CPM - Certified Plant Mechanic Power Plant Machinery Questions and Answers

Question 1

In a steam power plant, what is the primary function of a deaerator in the boiler feedwater system?

Accepted Answer

To remove dissolved gases, primarily oxygen, from the feedwater.

Answer

The primary purpose of a deaerator is to remove dissolved gases, especially oxygen and carbon dioxide, from the boiler feedwater. Dissolved oxygen is a major cause of corrosion and pitting in boiler tubes and other components, which can lead to equipment failure and reduced efficiency. By removing these gases, the deaerator protects the entire steam system.

Question 2

A plant mechanic observes a centrifugal pump making a loud rattling noise, similar to gravel passing through it, along with fluctuating discharge pressure and flow. Which of the following is the MOST likely cause of these symptoms?

Accepted Answer

Cavitation

Answer

The symptoms described—loud rattling or crackling noise, vibrations, and fluctuating pressure/flow—are classic signs of pump cavitation. Cavitation occurs when vapor bubbles form in a low-pressure area at the pump's suction and then violently collapse as they move into a higher-pressure zone, causing noise, damage to the impeller, and erratic performance.

Question 3

Which type of steam turbine is designed to exhaust steam at a pressure below atmospheric pressure into a condenser, maximizing the energy extracted from the steam for power generation?

Accepted Answer

Condensing turbine

Answer

A condensing turbine is specifically designed to expand steam to a very low pressure (a vacuum), which is maintained by a condenser. This large pressure drop across the turbine allows for the maximum amount of energy to be extracted from the steam, making it highly efficient for dedicated power generation. Back-pressure and extraction turbines, by contrast, exhaust steam at higher pressures for use in industrial processes.

Question 4

What is the principal role of an economizer in the boiler system of a power plant?

Accepted Answer

To preheat the incoming boiler feedwater using waste heat from flue gases.

Answer

An economizer is a heat exchanger that captures residual heat from the hot flue gases exiting the boiler. This captured heat is used to preheat the boiler feedwater before it enters the boiler drum. This process improves the overall thermal efficiency of the boiler by reducing the amount of fuel needed to turn the water into steam.

Question 5

In large rotating machinery like turbines and generators, what is the specific function of a thrust bearing?

Accepted Answer

To absorb and manage axial forces along the length of the shaft.

Answer

Thrust bearings are designed specifically to handle axial loads, which are forces that act parallel to the shaft's axis of rotation. In a turbine, for example, the flow of steam or gas creates a significant axial thrust that must be controlled to prevent the rotor from moving horizontally and making contact with stationary parts. Radial bearings, in contrast, support the weight of the shaft.

CPM - Certified Plant Mechanic Practice Test

CPM - Certified Plant Mechanic Practice Test

CPM - Certified Plant Mechanic Power Plant Machinery Questions and Answers