What type of pumps do hydraulics and most pneumatic systems use?

In hydraulic and most pneumatic systems, non-positive-displacement pumps are typically used because they continuously move fluid and maintain a steady flow. Unlike positive displacement pumps, which trap a fixed amount of fluid and force it out, non-positive-displacement pumps rely on a pumping mechanism, often involving an impeller or a similar component to create flow through the system.

Non-positive-displacement pumps are commonly found in applications where pressure needs to be maintained and where large volumes of fluid need to be moved efficiently rather than at a constant displacement. This makes them suitable for hydraulic systems that require a continuous flow to ensure the actuation of cylinders and motors efficiently.

The other types of pumps mentioned may have specific applications but do not meet the criteria of fluid flow characteristics suitable for hydraulics and most pneumatic systems. Centrifugal pumps, for instance, are a type of non-positive-displacement pump, but they are specifically designed for generating high flow rates while maintaining low pressure. Diaphragm pumps are positive-displacement pumps and are more suited for applications that require moving a specific volume of fluid at high pressure.