The rotor of the pump is a steel helix which has been coated in a smooth hard surface, normally chromium. The rotor fits inside a pump body or stator which normally is a rubber lined steel tube. The rubber core of the stator has a helical cavity, the wavelength of each helix in the rotor is exactly half that of the rotor. Rotation of the rotor inside the stator causes the cavity to progress along the pump thus inducing fluid flow. Compare to a Archimedes' screw.
Whilst progressive cavity pumps offer long life and reliable service, abrasive fluids will significantly shorten the life of the stator. The interface between rotor and stator is lubricated by the fluid being pumped, however if the pump is allowed to 'run dry' rapid deteriotation of the stator results.
Pumps of this type are often known as Mono pumps, after one of the major manufacturers - Mono Pumps