Progressive cavity pumps
A progressive cavity pump is usually made up of a single helix rotor revolving within a double helix stator (‘helix’ refers to the shape, which is like a corkscrew). As the rotor turns, being driven by the motor, it creates a space between the rotor and the stator which progresses down the pump from the suction to the discharge.
This design means the pump can be used from low flows to high flows, the flow being directly proportional to the speed of the pump. It’s also good for shear sensitive liquids (those which get thicker when they’re pumped, like cream, or thinner, like mayonnaise). And it’s self-priming, with a suction lift up to 8.5m.
The main disadvantage is that they can be relatively high maintenance, as both the rotor and stator will wear . The stator is particularly liable to damage if it’s pumped dry for any period of time.