单项选择题
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)
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相关考题
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Which of the following items is necessary for all waste heat boiler installations, regardless of design or manufacturer? （）
A.Control of evaporation
B.A separate means to prevent feed-water contamination
C.Power circulating pump
D.Super-heater -
单项选择题
Prior to lighting off a cold automatically fired auxiliary boiler, yon should （）.
A.check and regulate the water level
B.close the air cock once fires are lit
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D.crack the steam stop to assure protective steam flow -
单项选择题
After a normal, or safety shutdown, automatic combustion control systems for an auxiliary boiler are designed to prevent the immediate re-firing of a burner in order for the （）.
A.furnace to be re-purged
B.electric charge to buildup in the igniter
C.fuel pump to restart
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