One of the main functions of wearing rings, as used in a centrifugal pump, is to （）.

Gear pumps are widely used to transfer any one of the following but .

With reference to an axial piston pump, which one of the following statements is true?（）

Project（71）is an uncertain event or condition that，if it occurs，has a positive or a negative effect on at least one project objective，such as time，cost，scope，or quality．

Project ______is an uncertain event or condition that，if it occurs，has a positive or a negative effect on at least one project objective，such as time，cost，scope，or quality．

● Project（71）is an uncertain event or condition that, if it occurs, has a positive or a negative effect on at least one project objective, such as time, cost, scope, or quality.（71）

（）uses one or two high pressure pumps for all the cylinders with one more standby, while（）have a separate high-pressure pump for each cylinder.

If the relief valve on the discharge side of a hydraulic pump lifts, the cause could be （）.

The effective pump stroke of an individual port-and-helix fuel injection pump is determined by the （）

Jitter is an unwanted variation of one or more characteristics of a periodic signal in electronics and telecommunications and（）refers to call issues that cause variations in timing or time of arrival.

If the pump for a hydraulic anchor windlass is over heating, the cause may be （）.

If an operating bilge pump is developing good vacuum, but is unable to discharge any water, which of the following problems is the most probable cause?（）