单项选择题

In a closed diesel engine freshwater cooling system, the amount of coolant flowing through the heat exchanger is controlled by the （）.

A.suction pressure regulator
B.thermostatic bypass valve
C.sea water temperature
D.water level in the expansion tank

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单项选择题

Mechanical lubricators for diesel engine cylinders are usually small reciprocating pumps which are （）.

A.operated manually once an hour
B.operated until the engine has started
C.placed into operation only at maximum load
D.adjustable to meet lubrication requirements

单项选择题

Bottom blow valves are installed on auxiliary water-tube boilers to （）

A.remove suspended and precipitated solids from the boiler water
B.completely drain the boiler in an emergency situation
C.prevent hardened scale deposits in the water drum
D.remove floating impurities from the oily water surface