单选题When normal operating pressure is applied to the hydraulic oil used in a high-pressure system, the oil （）.A viscosity will decreaseB volume will increaseC volume will decreaseD pour point will be reduced

After installing a new hydraulic pump in a system, what special attention should be given to the hydraulic system?

A.The relief valves in the system should be readjusted

B.The filters and strainers should be checked frequently

C.All system pressure should be readjusted

D.The system should be drained and renewed with a fluid of different operating characteristics

If the suction pressure for an operating refrigeration compressor is below normal, the cause may be ______.

A.an excess of liquid refrigerant

B.the expansion valve overfeeding

C.a fouled compressor suction strainer

D.the compressor short cycling

Which of the listed pressure control valves would be used to establish the maximum operating pressure of a hydraulic system?

A.Pressure-reducing valve

B.Unloading valve

C.Counterbalance valve

D.Pressure-relief valve

Before performing any maintenance on a hydraulic system storing energy in an accumulator, you should

A.pressurize the system to test for leaks

B.bleed off all pressure within the system

C.operate the machine until it reaches normal temperature

D.disconnect the pump pressure control switch

Pressure drop in an operating hydraulic system is developed ______.

A.only by the pump as its primary function

B.by resistance to the fluid flow through the system

C.by the thermal input to the system's fluid

D.solely(单独地) by the charge applied by the accumulators

When using a fuel with a higher than normal sulfur content in an auxiliary four stroke diesel engine, you may

A.maintain higher than normal jacket water temperature

B.change the lube oil more frequently than normal

C.maintain a higher air-box temperature than normal

D.maintain a higher air-box pressure than normal