单选题The pumps press oil into the cross-head bearing gap when the load on the shell is at its lowest What is the meaning of “its” in the sentence above?（）A the cross-headB the pumpsC the shellD the load

Lubrication for the main reduction gears used with diesel engines is usually supplied by

A.oil from the main engine sump

B.an independent lube oil system

C.the stern bearing head tank

D.the stem bearing sump tank

材料：

Spark erosion is caused by a voltage discharge between the main bearing and journal surface. The cause of the potential is the development of a galvanic element between the ship’s hull, sea water, and the propeller shaft/crankshaft.

The oil film acts as a dielectric. The puncture voltage in the bearing depends on the thickness of the oil film. With increasing engine ratings, the specific load in the main bearing is increased. his will reduce the oil film thickness, and enable the discharge to take place at a lower voltage level.

Since the hydrodynamic oil film thickness varies through a rotation cycle, the discharge will take place at roughly the same instant during each rotation cycle, i.e. when the film thickness is at its minimum. The roughening will accordingly be concentrated in certain areas on the journal surface. In the early stages, the roughened areas can resemble pitting erosion. but later, as the roughness increases, the small craters will scrape off and pick up white metal-hence the silvery white appearance.

Therefore, to ensure protection against spark erosion, the potential level must be kept at maximum 80 mV, which is feasible today with a high efficiency earthing device. If an earthing device is installed, its effectiveness must be checked regularly. Spark erosion is only observed in main bearings and main bearing journals.

问题：

According to the paragraph one, a voltage between the main bearing and journal surface is produced by______.

A.propeller rotation

B.leakage from M/E electric control unit

C.a galvanic element

D.friction between the main bearing and journal surface

______engine ratings increase, the hydrodynamic oil film between the main bearing and journal surface is______.A.The lower/thinner

B.The higher/the thicker

C.The lower/thicker

D.The higher/thinner

When will the spark erosion take place on the journal surface during each rotation cycle?A.when the film thickness is at its minimum

B.when the film thickness is at its maximum

C.when the engine is on its compression stroke

D.when the engine is on its exhaust stroke

During the engine room watch keeping, which equipment must be noted to ensure protection against spark erosion?A.the antifouling plant

B.the earthing device

C.the main engine electric heating coils

D.the shaft generator

请帮忙给出每个问题的正确答案和分析，谢谢！

Which of the following statements concerning the lubrication of diesel propulsionengines used in vessels over 300 gross tons is most accurate? ( )

A.Lubrication systems using engine driven lube oil pumps do not require any additionalindependent arrangement when such arrangements have been proven reliable.

B.The use of engine driven pre-lube pumps is permitted on vessels with propulsionsystems developing less than 500 shaft horsepower.

C.When forced lubrication is used for propulsion engines , one independently drivenstandby pumps is to be provided in addition to the necessary pumps for normaloperation.

D.Lubrication systems where two oil coolers are fitted require a minimum of twotemperature control devices which may be actuated by similar sensors.

You are on a tanker discharging oil．When all of the oil that the main cargo pumps can handle is pumped out of a tank，the remainder is ______．

A.Stripped out and pumped directly ashore into the mainline as the remaining cargo tanks are pumped out with the main pumps

B.Stripped to one tank and then pumped out with the main pumps

C.Stripped out and pumped directly ashore after all the tanks have been emptied by the main pumps

D.Gravitated to the centers from the wings and pumped out with the main pumps

Adjust ______by means of lead wire.

A.the clearance of the main bearing

B.the diameter of main bearing

C.the gap of main bearing

D.the tolerance of main bearing

Which statement is TRUE concerning deep well self-priming pumps ________．

A.When loading oil cargo，it is always loaded via the discharge line through to the pump until the tank is topped off

B.Stripping systems are generally eliminated for the purposes of cargo handling

C.In recent years deep well pumps have become increasingly unpopular in product tankers and medium size crude ships

D.There is no danger of damaging the pump from overheating

In an engine with a pot-shaped piston, some lubricating oil from the main bearing will pass along a drilled passage in the crankshaft to the bottom end bearing and then up a connection rod to the

A.crosshead

B.crankpin

C.crank journal

D.gudgeon pin