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

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

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Steam Boilers, Engines, Nozzles and Turbines
The main object of a boiler trial is

To prepare heat balance sheet for the boiler
To determine the generating capacity of the boiler
All of these
To determine the thermal efficiency of the boiler when working at a definite pressure

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