What type of pumps create flow and are categorized as positive displacement pumps?

Positive displacement pumps are designed to move fluid by trapping a fixed amount and forcing (displacing) that volume into the discharge pipe. This principle creates a constant flow regardless of the system pressure. Hydraulic pumps fall under the category of positive displacement pumps because they utilize this mechanism to transfer hydraulic fluid effectively.

Hydraulic pumps are commonly used in various applications where reliable pressure and flow control are necessary, such as in hydraulic machinery and equipment. They can handle viscous fluids and provide a precise and consistent flow rate, features critical in hydraulic systems.

The other options refer to different types of pumping mechanisms. Pneumatic pumps deal with gases and typically rely on air pressure to create flow, while mechanical pumps may not adhere strictly to the positive displacement principle. Centrifugal pumps use rotational kinetic energy to move fluids, making them inherently different from positive displacement pumps, which rely on the displacement method rather than centrifugal force to move the fluid.