单项选择题
A.increased；decreased B.decreased；increased C.decreased；decreased D.increased；increased
The pressure head of a water pump is given in the unit ...
单项选择题The pressure head of a water pump is given in the unit of （）.
A.kg B.MPa C.mH20 D.None of the above
Which of the following are components of a mechanical s...
Which of the following are components of a mechanical seal? （） (1) stationary ring (2) rotational ring (3) packing (4)spring
A.(1), (2) and (3) B.(1), (2) and (4) C.(2), (3) and (4) D.None of the above
The gear, screw, and vane pumps are all classified as （...
单项选择题The gear, screw, and vane pumps are all classified as （）.
A.variable stroke pumps B.multistage pumps C.positive displacement pumps D.triple-ported pumps
