单项选择题
What is the purpose of pressure-vacuum relief valves? （）
A.Regulation of discharge pressure from cargo pumps B.Maintaining constant velocity in cargo lines C.Regulation of suction head on cargo pumps D.To maintain a tank or void at atmospheric pressure
单项选择题 What is the principle behind dynamic braking as used on an anchor windlass?（）
单项选择题 What is the holding power ratio of an anchor? （）
单项选择题 What is the function of wearing rings found on some centrifugal pumps? （）
