Which type of pump delivers a fixed quantity of fluid for each shaft revolution?

A positive displacement pump is designed to move a specific volume of fluid with each revolution of the pump's shaft. This is achieved by trapping a fixed volume of fluid in a chamber and then forcing it out through the discharge port as the pump operates. The defining characteristic of positive displacement pumps is their ability to provide consistent flow rates, irrespective of the system pressure (within certain limits). This makes them ideal for applications where precise fluid volumes are necessary.

In contrast, fluid displacement pumps and variable displacement pumps work under different principles. A fluid displacement pump typically refers to pumps that can displace a fluid but may not necessarily maintain fixed output per revolution. Variable displacement pumps change their output depending on the operational conditions, allowing for flow rate adjustments. Non-positive-displacement pumps, such as centrifugal pumps, rely on fluid velocity and pressure differences rather than trapping and displacing a fixed volume; hence, their flow rate can vary with changes in system pressure or resistance.

The positive displacement pump's reliability in delivering a precise volume of fluid per revolution is crucial for many industrial applications, making it the right answer in this scenario.