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
相关考题
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单项选择题
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 -
单项选择题
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 -
单项选择题
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
