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The expansion valve on a Freon system controls the ().
A . superheat of the gas leaving the compressor
B . back pressure in the evaporator
C . temperature of the icebox
D . superheat of the gas leaving the evaporator
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If the thermal bulb of an expansion valve is incorrectly placed at the center of the coil instead of the end, it will ().
A . increase the capacity of the coil
B . increase the superheat at the bulb
C . deliver more refrigerant to the coil
D . decrease the capacity of the coil
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A ruptured diaphragm in a thermostatic expansion valve will cause the valve to ().
A . open
B . close
C . remain in its position
D . flood the evaporator with refrigerant
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Which of the problems listed represents the major difficulty encountered with thermal expansion valve operation?()
A . Lube oil passing through the system
B . Moisture or foreign matter collecting at the valve seat and orifice
C . Variable spring tension caused by the changing temperature
D . Frost on the liquid line
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Compared to the amount of concentrated foam liquid used,the amount of low expansion mechanical foam produced is().
A . 97 times greater
B . 94 times greater
C . 10 times greater
D . 2 times greater
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Which of the following statements regarding low expansion foam and its application is INCORRECT?().
A . Foam should not be used on electrical fires
B . One kilo of low expansion foam solution produces much more foam
C . Foam is only efficient when it covers the top of burning combustibles
D . A stream of foam should be deflected off the deck in order to best agitate the fire
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A feeler or thermal bulb is used for the expansion valve to ().
A . detect the temperature
B . detect the pressure
C . heat the refrigerant
D . accelerate the refrigerant
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The rate of expansion of heated fuel oil varies with the ().
A . conductivity
B . viscosity
C . volume
D . specific gravity
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() allows for expansion and water make up in the water cooling system.
A . A top tank
B . A head tank
C . A head valve
D . A drain tank
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The thermal expansion valve responds to the()
A . amount of superheat in the vapor leaving the coil
B . amount of superheat in the liquid
C . temperature in the evaporator coils
D . pressure in the evaporator coil
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The four strokes are called suction, compression, expansion and exhaust, but only () stroke provides the power to drive the ship.
A . suction
B . compression
C . expansion
D . exhaust
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The bulb for the thermal expansion valve is located()
A . in the middle of evaporator coils
B . near the evaporator coil outlet
C . near the evaporator coil inlet
D . on the bottom row of evaporator coil
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A cracked diaphragm in a thermostatic expansion valve will cause the valve to ().
A . return to a neutral position
B . flood the evaporator
C . open
D . close
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An alarm device inserted between the deaerating tank and the expansion tank can notify the on-watching crew that ()
A . the expansion tank is lack of water
B . the expansion tank is over flowing
C . there is something wrong with the cooling system
D . there is something wrong with the engine
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Which of the listed statements is a characteristic of the liquid charged power element used with thermostatic expansion valves?()
A . At the designed operating temperature, the liquid refrigerant charge has changed to a vapor
B . The liquid refrigerant tends to collect at the bellows or diaphragm and reduces the valve sensitivity
C . The sensing bulb is empty of liquid refrigerant charge at the designed operating temperature
D . The sensing bulb is never emptied of liquid refrigerant under normal operating conditio
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When a refrigeration compressor is in the ‘off’ cycle, the thermal expansion valve will().
A . always be wide open when the compressor restarts
B . continue to operate as if the system were in operation
C . remain open until evaporator pressure equalizes, then close until the compressor restarts
D . always be completely closed until the compressor restart
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Cultural globalization is the ________ of economic globalization.
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The organizational structure may be changed with the growth and expansion of business operations.
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What is the reason for the possible expansion of the PC market?
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In the tree-tiered concept of globalization, political globalization is the base and core.
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Expansion work is the work of expansion ().
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What happened during the agricultural expansion in the southern Great Plains?
A.People improved the soil by planting wheat.
B.Raising cattle and other livestock became less common.
C.Most of the landowners became farmers.
D.Much of the grassland was destroyed.
此题为多项选择题。
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When a refrigeration compressor is in the ‘off’ cycle, the thermal expansion valve will .
A.always be wide open when the compressor restarts
B.continue to operate as if the system were in operation
C.remain open until evaporator pressure equalizes, then close until the compressor restarts
D.always be completely closed until the compressor restarts
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Among the four strokes of a four-stroke diesel engine,suction and expansion strokes are the upward strokes.()
此题为判断题(对,错)。