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
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A.filled with water
B.purged
C.cleared of air
D.None of the above is true
A.Safety valves
B.Water tubes
C.Steam stop valves
D.Blow down valves
A.water-tube
B.fire-tube
C.exhaust gas
D.None of the above is true
A.water-tube
B.fire-tube
C.exhaust gas
D.none of the above
A.scaled
B.informed
C.leaky
D.deformed
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The rate of heat transfer from a hot region to a cold region is affected most by the （）.
Heavy wear in a particular area of the inner circumference of a packing ring may be caused by （）.
Thermostatic expansion valves can be adjusted for （）.
Pitting in the suction areas of a centrifugal pump bronze impeller is usually caused by （）.
When the steering gear is in operation, you should （）.
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If the suction pressure at the refrigeration compressor is below normal, the cause can be（）.
The amount of fluid friction or internal friction inherent in a mineral lubricating oil is reflected as a measure of its （）.
Low compressor head pressure in a refrigeration system can be caused by（）.
One cause of high head pressure occurring in a refrigeration system can be （）.