單項(xiàng)選擇題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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1.單項(xiàng)選擇題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

2.單項(xiàng)選擇題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

3.單項(xiàng)選擇題（） are mounted in pairs to protect the boiler against overpressure.

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

4.單項(xiàng)選擇題In a （） boiler the hot gases from the furnace pass through the tubes while the water is on the outside.

A.water-tube
B.fire-tube
C.exhaust gas
D.None of the above is true

5.單項(xiàng)選擇題In a （） boiler the water flows through the inside of the tubes while the hot gases pass around the outside.

A.water-tube
B.fire-tube
C.exhaust gas
D.none of the above