单项选择题

The donkey boiler may be given a bottom blow （）

A.to raise water level
B.only while making steam
C.to remove scum
D.when fire are secured

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单项选择题

A.drop as the boiler warms up
B.rise as the boiler warms up
C.remain unchanged until the boiler is hot enough
D.rise and fall with the steam demand

单项选择题

A.filled with water
B.purged
C.cleared of air
D.None of the above is true

单项选择题

A.Safety valves
B.Water tubes
C.Steam stop valves
D.Blow down valves