Mechanical Interview Questions 9 contains questions
81. What is the difference between Bolt and Screw?
82. What is the differences between gas turbine and a
steam turbine?
83. What is operating pressure?
84. What are the safety valves? How many on each boiler?
85. What is a sentinel valve?
86. What is the function of Hydrogen seals work on a
generator?
87. How is the excess discharge pressure prevented?
88. Which two seal oil pumps are driven from the same
motor?
89. When does Emergency Seal Oil Pump automatically
start?
90. What is the consequence of not maintaining hydrogen (or air) pressure in generator casing at a value above atmospheric pressure when seal oil system is in service?
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81. What is the difference between Bolt and Screw?
The main difference was based on the load acting on it, and the size. For smaller loads, screws are enough but in case of greater-loads, bolts are to be used.
In bolt we give centrifugal force or tangential force and screw we give axial force for driving.
82. What is the differences between gas turbine and a steam turbine?
Gas turbine works on Bryton cycle where as steam turbine works Rankine cycle.
Construction, operation of a gas turbine are entirely different to steam turbine.
Gas turbine has a compressor to compress the combustion air, a combustion chamber to burn the fuel and a turbine section to extract the work for burning fuel.
Steam turbine is just has a turbine section to extract the work from steam.
83. What is operating pressure?
The amount of pressure nearest the point of performing work at the output end of a pneumatic system. The system operating pressure is used to specify the capability of valves and actuators.
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84. What are the safety valves? How many on each boiler?
A valve opening automatically to relieve excessive pressure, especially in a boiler.
There are normally two to six safety valves provided in the drum depending upon the capacity.
The super heater outlet will have one to three safety valves on either side of the boiler. There will be an electromatic relief valve on the super heater pipe in addition.
This valve will be set at lower pressure than the lowest set safety valve on the super heater.
The reheater pipes both at the inlet and outlet side will also have safety valves which can range from two to eight both in the inlet and outlet of the reheater put together.
85. What is a sentinel valve?
Sentinel valves are simply small relief valves installed in some systems to warn of impending over pressurization.
Sentinel valves do not relieve the pressure of the system. If the situation causing the sentinel valve to lift is not corrected, a relief valve (if installed) will lift to protect the system or component.
If a relief valve is not installed, action must be taken quickly to secure the piece of equipment or system to reduce the pressure.
86. What is the function of Hydrogen seals work on a generator?
Provide a seal between the generator housings and rotor shaft to maintain the pressurized hydrogen gas inside the generator.
Also, provides a trap-vent system to prevent the release of hydrogen into the turbine generator lube oil system and building atmosphere.
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87. How is the excess discharge pressure prevented?
Pressure relief valves on the discharge side of each seal oil pump relieves back to seal oil system.
88. Which two seal oil pumps are driven from the same motor?
Main seal oil pump and re-circular seal oil pump; both are driven by Main seal oil pump motor.
89. When does Emergency Seal Oil Pump automatically start?
When its pressure switch senses Main Seal Oil Pump discharge pressure reduced to 78 PSI.
90. What is the consequence of not maintaining hydrogen (or air) pressure in generator casing at a value above atmospheric pressure when seal oil system is in service?
Failure to do so will cause excessive seal oil to be drawn into the generator.