單項選擇題The crankcase of many diesel engines are kept under a slight vacuum by the （）.

A.scavenging action of the piston
B.piston type vacuum pump taking suction off a differential manometer
C.gland exhausting manometer
D.crankcase exhaust fan


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1.單項選擇題Fins are installed on the generating tube surfaces in waste heat boilers to （）.

A.prevent soot fires in the exhaust system
B.prevent exhaust gas erosion of the tubes
C.increase the velocity of exhaust gas flow
D.increase the rate of heat transfer

2.單項選擇題On a medium-speed main propulsion diesel engine, the crank-pin or crank journal bearings receive lubricating oil from （）.

A.a spindle lubricator
B.an oil jet
C.internal splashing
D.drilled passages in the crankshaft

3.單項選擇題The rate of cylinder lubricating oil metered to each cylinder of a large low-speed main propulsion diesel engine is （）

A.the same, whether at sea, or during maneuvering
B.adjusted during each hour of operation while at constant RPM
C.higher at sea than while maneuvering
D.lower at sea than while maneuvering

4.單項選擇題The crankcases of many diesel engines are kept under a slight vacuum to （）

A.improve fuel economy
B.increase the air charge velocity
C.reduce the risk of explosion
D.all of the above

5.單項選擇題Which of the following conditions could cause the feed pump for an auxiliary boiler to lose suction?（）

A.Increased suction head pressure
B.Decreased feedwater temperature
C.Pump recirculating line being open too much
D.Excessive feedwater temperature