A pump with significant clearance between the rotating surface and the stationary passage does not have what?

A pump with significant clearance between the rotating surface and the stationary passage effectively lacks positive displacement characteristics. Positive displacement pumps work by trapping a fixed volume of fluid and forcing it through the discharge. This mechanism relies on minimal clearance to ensure that a consistent volume is moved with each cycle or rotation.

When there is significant clearance, fluid can easily bypass the rotating element instead of being displaced, leading to a loss of the very pressure and flow that define positive displacement action. As a result, the pump cannot maintain its intended operation, and the efficiency suffers since the required volume of fluid is not effectively moved in the desired manner.

Therefore, while pumps can be designed for various applications with varying types of impeller and casing configurations, significant clearance directly compromises the principle of positive displacement, underscoring the importance of tight tolerances in such designs.