單項選擇題Excessive alkalinity of the water in an auxiliary boiler can cause （）.

A.caustic embrittlement of the boiler metal
B.acidic corrosion of the boiler metal
C.hard scale deposits on the boiler tubes
D.etching of the heat exchange surfaces


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1.單項選擇題The purpose of the delivery check valve used in a diesel fuel injection jerk pump is to （）.

A.assist in a quick cutoff of fuel injection
B.allow oil backflow from the injector to the helix
C.reduce fuel oil pressure between injection strokes
D.meter the quantity of fuel delivered

3.單項選擇題If over a period of weeks the air-box pressure of a turbo-charged, diesel engine, operating at full load, appears to be dropping off, the cause can be （）.

A.open air-box drains
B.loss of cooling water to the diffuser
C.gradual fouling of the air filters
D.improperly timed exhaust valves

4.單項選擇題The most common cause of scale formation in an auxiliary boiler is （）

A.concentrations of calcium sulfate in the boiler water
B.fuel oil in the feed water
C.improper treatment of the feed water with calcium sulfate
D.excessive feed water alkalinity

5.單項選擇題For proper operation, auxiliary boiler feed water must have which of the following characteristics?（）

A.High oxygen concentration
B.Low pH
C.Proper alkalinity
D.All of the above