How do progressive cavity pumps work?

Progressive cavity pump working principle

A progressing cavity (PC) pump employs a positive displacement principle. A typical PC features a suction inlet which feeds into an elongated casing. Within this casing sits a helical 'worm' rotor and stator assembly. The rotor helix is shaped off-set to the stator creating cavity spaces in the assembly which are formed by temporary seals as the rotor contacts the surface of the stator. As the rotor begins to move in an eccentric fashion, the cavities form, draw in product and are 'progressed' along the assembly and the product is expelled through the discharge port.    

What sort of fluids are progressing cavity pumps used for?

Progressing cavity pumps are often installed for handling viscous fluids at high flow rates or where a high discharge pressure is required with a smooth flow.

Typical fluids may include slurry, mashes, pulps, dough from waste water treatment plants, anaerobic digestion facilities and paper recycling plants.

As the pump flow rate is proportional to the speed the pump can be used for the dosing of viscous fluids such as additives and chemicals.

Types of progressing cavity pump

PC pumps can be adapted and specified with a range of accessory components and configurations to accommodate the difficult fluids it is expected to handle.

Examples include:

  • The feed inlet with different screw and paddle feeders to break up solids.
  • Mechanical seal arrangements to protect against highly abrasive wear
  • Hygienic-compliant materials and configuration
  • Compact build dosing type pumps
  • Vertical build units for barrel emptying
  • Progressing cavity pumps must not run dry as the heat generated by the rotor and stator can cause failure - However there are many accessory additions to protect against this, both from the suction side and on the pump itself. 

Geometries

Progressing cavity pumps are available with various geometries, typically in different ratios, which effect the degree of entry of the product into the next cavity and the degree of efficiency and sealing between each cavity. 'Standard' geometry is usually best for thicker material as the pitch allows for the viscosity of the product whereas long geometry with shallow curves and larger surface contact between the rotor and stator provides more efficiency.