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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相关考题
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单项选择题
When steam is being raised on a boiler, the water level will normally （）.
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
The furnace of an oil fired boiler should be （） before the operating burner is lit.
A.filled with water
B.purged
C.cleared of air
D.None of the above is true -
单项选择题
（） are mounted in pairs to protect the boiler against overpressure.
A.Safety valves
B.Water tubes
C.Steam stop valves
D.Blow down valves
