Positive Displacement Pumps

Basic Knowledge

A positive displacement pump makes a fluid move by trapping a fixed amount and displacing that trapped volume into the discharge pipe. (The energy is transferred to the fluid hydrostatical.) In the hydrostatic transfer of energy a displacement body reduces a working chamber filled with fluid and pumps the fluid into the intake pipe. In this case, the displacement body applies a pressure to the fluid. When the working chamber expands it is refilled with fluid from the intake pipe.

Positive displacement types

A positive displacement pump can be further classified according to the mechanism used to move the fluid:

  • Rotary positive displacement
  • Oscillating positive displacement

Examples of rotary positive displacement pumps

There are several types of rotary lobe pumps available:

Schematic drawing Name Description
Positive displacement pump example 1: rotary lobe pump Rotary lobe pump Similar like gear pumps, rotary lobe pumps have to rotors to forward the liquid.
Positive displacement pump example 2: gear pump Gear pump Two rotors formed like a gear handle the pumping media. Gear pumps are cheap because the synchronisation of the rotors are done inside the product chamber.
Positive displacement pump example 3: impeller pump Impeller pump Impeller pumps have only one rotor made of elastic rubber.
Positive displacement pump example 4: vane pump Vane pump Vane pumps are also positive displacement pumps. As the rotor rotates the vanes move inside the cavity and pushing the liquid chamber forwards.
Positive displacement pump example 5: peristaltic pump Peristaltic pumps A rotor moves circular and pushes the media inside a flexible hose forwards. Although this pump has a high pulsation, they have some advantages at particular applications.

The advantages and disadvantages of each type can be found in this pump comparison.