The principal function of stop valve is to
1
control the flow of steam from the boiler to the main pipe and to shut off the steam completely when required.
2
empty the boiler when required and to discharge the mud, scale or sediments which are accumulated at the bottom of the boiler.
3
put off fire in the furnace of the boiler when the level of the water in the boiler falls to unsafe limit.
4
increase the temperature of saturated steam without raising its pressure.