A distinction is made according to the movement type of the displacer. The types are rotary and reciprocating positive displacement pumps.Oscillating positive displacement pumps include
- Piston pump
- Diaphragm pump
The following constructions are counted among the rotating positive displacement pumps:
- Screw pump
- Progressing cavity pumps (eccentric screw pumps)
- Rotary lobe pump
- Gear pump
- Screw pump
- Peristaltic pump
In opposition to the centrifugal pumps the positive displacement pumps are suitable for a very high viscosity of the pumped fluid. Furthermore the reciprocating pumps can be suitable for metering and dosing applications.
In a narrower sense, in contrast to blowers and compressors for gases and compressible media, pumps for incompressible media are referred to as liquid pumps. This means that the volume of the fluid remains approximately constant as the pressure increases. In practice, this also includes liquid mixtures with a low solid or gas content.Depending on the direction of the energy flow, pumps belong to the working machines.
