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.
As a displacement element, they have an elastic diaphragm whose axial movement is caused either by a direct drive by means of a drive rod or indirectly by transmitting the displacement pressure of a plunger.
There are different types of piston pumps (reciprocating piston pumps):
- the submersible piston pump, also called plunger pump,
- the disc piston pump and
- the diaphragm pump.
By asynchronously opening and closing the inlet respective outlet of the pump chamber, the fluid will moved in the pump chamber and then pressed to the discharge side.
Reciprocating pumps are generally used for applications that require relatively low flows and high pressures. Since each cylinder delivers a definite volume of liquid to the system, these pumps are also applicable for dosing and metering tasks. The disadvantage against rotating pumps is the pulsating operation.
