Steam Boilers, Engines, Nozzles and Turbines
Blow off cock in a boiler is used to

Control the flow of steam from the boiler to the main pipe and to shut off the steam completely when required
Put off fire in the furnace of the boiler when the level of water in the boiler falls to an unsafe limit
Empty the boiler when required and to discharge the mud, scale or sediments which are accumulated at the bottom of the boiler
Increase the temperature of saturated steam without raising its pressure

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Steam Boilers, Engines, Nozzles and Turbines
In an ideal impulse turbine, the

Absolute velocity at the inlet of moving blade is equal to that at the outlet
Axial velocity at inlet is equal to that at the outlet
Relative velocity at the inlet of the moving blade is equal to that at the outlet
Whirl velocity at inlet is equal to that at the outlet

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Steam Boilers, Engines, Nozzles and Turbines
The relative efficiency is defined as the

Ratio of thermal efficiency to Rankine efficiency
Ratio of heat equivalent to indicated power to the energy supplied in steam
Product of thermal efficiency and Rankine efficiency
Ratio of brake power to the indicated power

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Steam Boilers, Engines, Nozzles and Turbines
In forced circulation type boiler

Water is converted into steam in one pass without any recirculation
Water is supplied in drum and through down comers located in atmospheric condition it passes to the water wall and rises to drum in the form of mixture of water and steam
Heating takes place at bottom and the water supplied at bottom gets converted into the mixture of steam bubbles and hot water which rise to drum
Feed pump is employed to supplement natural circulation in water wall type furnace

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