This set of Thermal Engineering Questions and Answers for Freshers focuses on “Boiler Mountings – 2”.
1. What is the function of fusible plug?
a) Protects the boiler from overheating
b) Prevents mixing of water and steam
c) Regulated the flow of steam outside boiler
d) It is opened to increase the flow of air for combustion
Explanation: Overheating damage to the boiler is prevented by fusible plug. Overheating occurs when water level is low. It Is fitted above the fire box. When water level falls below the level of fusible plug, it is exposed to steam and it melts. Steam and water rush to the fire box and extinguish the fire which prevents overheating of boiler.
2. Which of the following statements about fusible plug is FALSE?
a) It extinguishes fire when water level is low
b) It protects the boiler from overheating
c) It should have a very high melting point
d) It needs to be renewed after a period of time
Explanation: The melting point of fusible plug should be less than the temperature of the steam getting generated, since the fusible plug is supposed to melt when it comes in contact with the steam. Fusible plugs should usually be replaced after a period of about 2 years.
3. In fusible plug, the fusible metal is protected from fire by flange on the hollow gun metal plug.
Explanation: The fusible metal is to be melted only by the steam and not by the hot gases released from the combustion in the fire-box. The fusible metal is therefore protected from fire by flange on the hollow gun metal plug.
4. Which of the following statements about blow-off cock is FALSE?
a) It is used to discharge the mud that has settled at the bottom
b) It is used to empty the boiler for cleaning
c) Scale and sediments are also removed when the blow-off cock is opened
d) It is used to fill the boiler with water
Explanation: Blow-off cock is used to remove or blow out mud, sediments and scales that had settled down at the bottom of the boiler. Also it is used to empty the boiler when it is required to be cleaned. Feed check valve is used to fill water inside the boiler.
5. In a fusible plug, the substance that melts when it comes in contact with the steam is called _____
b) Meting wax
c) Fusible metal
d) Fusible wax
Explanation: Fusible metal melts when it comes in contact with the steam. Normally fusible plug is completely inside the water. When the water level falls down and the fusible plug is exposed to steam, the fusible metal melts and the fusible plug opens. The steam and water being under pressure rush through the opening and extinguish the fire.
6. What is the function of a feed check valve?
a) It regulates the flow of hot gases from the fire-box
b) It controls the flow of air to the combustion chamber
c) It controls the supply of steam outside the boiler
d) It controls the supply of water to boiler
Explanation: The function of feed check valve is to control the supply of water to the boiler. It also prevents the back flow of water when the pump is switched-off. It is installed slightly below the normal water level in the water space.
7. The part of the feed check valve which moves up and down automatically under the pressure of water on its gun metal seat is called _____
a) Check valve
b) Fusible plug
d) Safety valve
Explanation: Check valve moves up and down automatically under the pressure of water on its gun metal seat. It is designed such that it only allows water flow only in direction. This prevents the back-flow of water from the boiler to the pipe.
8. Which of the following statements about feed check valve is FALSE?
a) It controls the flow of water
b) It only allows flow of water in one direction
c) It is fitted on top of the boiler shell
d) It consists of check valve which automatically moves up and down under pressure of water
Explanation: The feed check valve is mounted in the water space slightly below normal level of water. It controls the flow of water in the boiler and also prevents the back-flow of water from the boiler back to the pipe when the pump is switched off.
9. Which of the following is NOT a boiler mounting?
a) Steam stop valve
b) Man hole
d) Pressure gauge
Explanation: Steam stop valve, Man hole and pressure gauge are boiler mountings. Economizer is a boiler accessory. Boiler accessories increase the efficiency of the boiler while boiler mountings are attached for safe operation of the boiler.
10. Which of the following statement about stop valve (or junction valve) is FALSE?
a) It regulates the flow of steam
b) Fitted at top of the boiler
c) It connects boiler with the steam pipe
d) The smaller sized valve is called junction valve
Explanation: The smaller diameter valve that connects boiler and steam pipe is called stop valve and the larger one is called junction valve. It is mounted on top of the boiler shell. It is used to regulate the flow of steam outside the boiler.
11. Where is feed check valve mounted?
a) On top of the boiler shell
b) At the bottom of the boiler shell
c) Above the water level to be maintained
d) Slightly below the water level to be maintained
Explanation: The feed check valve is fitted slightly below the normal water level. The valve is used to supply water to the boiler. Being below normal water level there is a chance of back-flow of water to the pipe. The feed check valve is designed such that it prevents water from flowing back.
12. Feed check valve is used to empty the boiler when it is required to be cleaned.
Explanation: A feed check valve is used to supply water to the boiler. The boiler is emptied using the blow-off cock. Boilers are emptied for cleaning, inspecting and repairing. Bow-off cock is also used to remove the mud, scales and sediments that have settled down at the bottom of the boiler.
Sanfoundry Global Education & Learning Series – Thermal Engineering
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