單項(xiàng)選擇題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


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1.單項(xiàng)選擇題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

2.單項(xiàng)選擇題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

3.單項(xiàng)選擇題Although lube oils used in the main lubricating service systems should have a relatively high flash point to avoid ignition, they can create smoke and fire hazards when they（）

A.are exposed to a vacuum
B.come in contact with extremely hot surfaces
C.are reduced in temperature to just above the pour point
D.become extremely agitated or aerated

4.單項(xiàng)選擇題Compensated flow control or constant flow valves are used in hydraulic systems to（）

A.compensate for major leaks in the system
B.maintain the original fluid viscosity
C.allow for changes in pressure and temperature within the system
D.assure constant fluid temperature

5.單項(xiàng)選擇題To avoid damaging the components of a printed circuit board when testing it with a DC volt-ohmmeter, you should （）

A.ground the board
B.avoid reversing the polarity of the leads
C.isolate sensitive components with heat sinks
D.all of the above