单项选择题
A.in series B.in parallel C.assembled D.together
Sealing in pump shaft is achieved by means of the （）.A....
单项选择题Sealing in pump shaft is achieved by means of the （）.
A.gasket B.packing C.washer D.spring
（） is the breakdown of surface tension between oil drop...
单项选择题（） is the breakdown of surface tension between oil droplets in an oil water mixture which causes them to join and increase in size.
A.Wear B.Contaminating C.Coalescence D.Coarse separating
Centrifugal pumps are popular because they are very sim...
单项选择题Centrifugal pumps are popular because they are very simple in construction,and produce smooth, constant, （） discharge.
A.non-pulsating B.pulsating C.positive D.non-positive
