What feature distinguishes a positive displacement pump from other types of pumps?

A positive displacement pump is characterized by its ability to maintain a constant flow rate regardless of the pressure in the system. This feature is fundamental to its operation. Positive displacement pumps work by trapping a fixed amount of fluid within their chambers and then forcing that volume into the discharge pipe, creating a steady and consistent flow. This means that even if the system encounters resistance or a change in pressure, the flow rate remains relatively constant, making these pumps particularly useful in applications where uniform flow is crucial.

The other features listed represent characteristics of different types of pumps. For instance, pumps that change speed based on pressure typically belong to the category of centrifugal pumps, which adjust their flow rate depending on the load conditions. Pulsing flow is also common in certain types of pumps, like diaphragm or gear pumps, but it doesn't apply to the steady operation of positive displacement pumps. Minimal maintenance can vary widely among different pump designs, so it's not a defining feature of positive displacement pumps either. Thus, the ability to maintain a constant flow rate despite pressure changes is what distinctly defines positive displacement pumps.