单项选择题

CFC refrigerants exposed to high temperature or direct flame, will decompose and may produce（）

A.methyl chloride
B.ammonia
C.hydrofluoric acid
D.ozone

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单项选择题

The major difference between the discharge and suction valves installed in most low pressure, reciprocating air compressors is that（）

A.one valve seats upwards, while the other seats downwards
B.the reed valves used on the discharge are made substantially thicker and heavier than the suction valves
C.the suction valve springs exert a greater tension than the discharge valve springs
D.the discharge valve springs exert a greater tension than the suction valve springs

单项选择题

Which of the following problems will occur if the internal drain at either end of a hydraulic, two-way, spool-type directional control valve cylinder were to become plugged?（）

A.The reservoir would become vapor bound
B.The valve would be placed in hydraulic lock
C.The spring loaded relief ports would open
D.The buffering chambers would be unable to function

单项选择题

Hydraulically, servo-operated, automatic, change over valves, utilized in a two ram hydraulic steering gear, serve to（）

A.allow an alternate main pump to start in the fully loaded condition thus developing immediate full torque
B.prevent either main pump from being hydraulically motored when idle by cross pressure flow
C.prevent both units from operating simultaneously which could result in doubling the flow of oil and pressure leading to over pressurization of the system
D.all of the above