单项选择题
In most pumps and pump motors overpacking the ball bearings full of grease will result in （）
A.moisture emulsification of the bearing grease
B.insufficient circulation and overheating of the bearing
C.proper grease circulation to cool the bearing
D.sliding friction between balls and races
相关考题
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单项选择题
Aqueous Film Forming Foam (AFFF), commonly known as ‘light water’, is especially suitable for fighting （）
A.oil fires in the engine room bilges
B.class B fires in paint lockers
C.any class D fire
D.all of the above -
单项选择题
Which of the following statements concerning the water tube and fire tube boilers is not true?（）
A.natural circulation of the water in the water tube boiler is better than that in the fire tube boiler
B.for the same output the water tube boiler will carry less mass of water compared with the fire tube boiler
C.the water tube boiler will cost shorter time for steam raising
D.the water tube boiler require lower skill in operating and maintaining -
单项选择题
Which one of following statement is not true concerning the suitable sites of the direct acting relief valve and the pilot operated relieve valve?（）
A.the direct acting relief valve is used for controlling lower flows and pressure
B.the pilot operated relief valve is used for controlling higher flows and pressure
C.the pilot operated relief valve is used for controlling lower flows and pressure
D.the controlling accuracy of direct acting relief valve is worse than that of the pilot operated relief valve
