Vane pumps, piston pumps, and gear pumps are the foremost types of hydraulic pumps
Gear pumps – uses gears to pump fluid by displacement. Hydraulic gear pumps are one of the most common types of pumps. There are several advantages and disadvantages to gear pumps. The advantages are: high speed, high pressure, and quiet operation. The disadvantages are: the use of four bushings in the liquid area and fixed end clearances.
Rotary vane pumps – are positive-displacement. They include a ring mounted inside a cylindrical case. There are a number of radial slots in which sliding vanes are located. Mounted to the case is the ring and the vanes are designed to press against the inside wall of the case. Hydraulic pressure or spring force or centrifugal force as the ring is rotated will cause the vane to be forced against the wall.
Axial piston pumps – are positive displacement. There are several pistons in a circular arrangement in a cylinder block.
Radial piston pumps – a circular arrangement of hydraulic pistons, and valves which allow pressures greater than 650 Bar (~10,000 psi) to be built.
Screw pumps – positive displacement pumps. Have one or more screws that rotate to transfer high or low viscosity fluids along an axis.