A.either all the way open or all the way closed
B.normally open
C.throttled depending on load
D.controlled by suction pressure
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When a hydraulic vane pump is working, which of the following is in contact with the vanes?（）
(1) the rotor
(2) the internal surface of the housing
(3) the external surface of the housing
A.(1) only
B.(2) only
C.(1) and (2)
D.(1), (2) and (3)
A.Control of evaporation
B.A separate means to prevent feed-water contamination
C.Power circulating pump
D.Super-heater
A.check and regulate the water level
B.close the air cock once fires are lit
C.blowdown the gage glass
D.crack the steam stop to assure protective steam flow
A.furnace to be re-purged
B.electric charge to buildup in the igniter
C.fuel pump to restart
D.drum level to stabilize
A.The blow down valve
B.The scum valve
C.The air release cock
D.Scot-blower
最新試題
Heavy wear in a particular area of the inner circumference of a packing ring may be caused by （）.
An excessive charge of refrigerant in an air-cooled refrigeration system can cause （）.
An increasing head pressure in a refrigeration system, without any corresponding change in the cooling water inlet temperature, would probably be caused by （）.
The major source of chemical contaminants in hydraulic fluid is （）.
Low compressor head pressure in a refrigeration system can be caused by（）.
If the thermal bulb of an expansion valve is incorrectly placed at the center of the coil instead of the end, it will （）.
A salinity indicator is used to determine the （）.
Which of the following problems could cause the high pressure cutout switch to shut down the compressor in a refrigeration system?（）
The usual symptoms of cavitation in a centrifugal pump is （）.
The control mode in which the final control element is moved from one of two flexed positions to the other is known as （）.