water passes through the tubes which are surrounded by flames and hot gases

the flames and hot gases pass through the tubes which are surrounded by water

forced circulation takes place

none of these

ratio of heat actually used in producing steam to the heat liberated in the furnace

ratio of the mass of steam produced to the mass of total water supplied in a given time

ratio of the heat liberated in the furnace to the heat actually Used in producing steam

none of the above

condenser efficiency

vacuum efficiency

nozzle efficiency

boiler efficiency

blow off cock

feed check valve

steam stop valve

none of these

control the flow of steam from the boiler to the main pipe and to shut off the steam completely when required

empty the boiler when required and to discharge the mud, scale or sediments which are accumulated at the bottom of the boiler

put off fire in the furnace of the boiler when the level of water in the boiler falls to an unsafe limit

increase the temperature of saturated steam without raising its pressure