NACHI piston pump

Radial piston pump: normally used for very high pressure at small flows.
Piston pumps are more expensive than gear or vane pumps, but provide longer life operating at higher pressure, with difficult fluids and longer continuous duty cycles. Piston pumps make up one half of a hydrostatic transmission.

Axial piston pump: many designed with a variable displacement mechanism, to vary output flow for automatic control of pressure.