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单选题

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
Counterbalance valve
D. Pressure-relief valve

单选题

Which of the following modes of heat transfer does NOT require any physical contact between a warmer and a cooler substance?（）

A. Radiation
B. Conduction
C. Natural convection
D. All of the above

单选题

A sight glass is installed in the liquid line to indicate the condition of the refrigerant charge and may also indicate the （）.

A. condition of the expansion valve
B. moisture in the system
C. condition of the compressor suction valves
D. condenser temperature

单选题

When a flash-type evaporator is to be secured for an extended period of time, the entire unit should be drained, cleaned, and （）.

A. completely filled with saltwater
B. filled with de-scaling compound
C. tightly closed to exclude air
D. vented to the atmosphere

单选题

Which of the listed statements is a characteristic of the liquid charged power element used with thermostatic expansion valves?（）

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

单选题

（） is the breakdown of surface tension between oil droplets in an oil water mixture which causes them to join and increase in size.

A. Wear
B. Contaminating
Coalescence
D. Coarse separating

单选题

Which of the following terms represents the form of heat removed from the refrigerant in the condenser of a refrigeration system?（）

A. Latent heat of vaporization
B. Heat of compression
C. Superheat
D. All of the above

单选题

Among the basic categories of equipment, which of the following is used to convert hydraulic energy into continuous rotary motion?（）

A. Hydraulic pumps
B. Valve
C. Hydraulic cylinders
D. Hydraulic motor

单选题

Machinery driving fuel oil transfer and fuel oil service pumps must be fitted with a remote means of stopping the machinery from （）.

A. within the space concerned
B. outside the space concerned
C. the throttle station
D. within the fire room

单选题

When the union purchase derrick is operated, one derrick is positioned over the quayside and the other almost vertically over the （）.

A. dock
B. hold
C. pedestal
D. machinery space

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