In brief
A progressive cavity pump is a positive displacement pump in which a helical rotor turning in an elastic stator forms cavities that travel along the pump.
Contents
What is Progressive cavity pump?
The metal rotor turns eccentrically in the stator, which is usually made of an elastomer. Sealed cavities form between the two and move continuously from the suction side to the discharge side. As a result, the pump delivers almost pulsation-free and gently. It is suitable for viscous, abrasive, solids-laden or shear-sensitive media such as sludges, pastes, adhesives, paints and food masses.
The drive is via a joint, such as a cardan or pin joint, which compensates for the eccentric movement. The number of stages determines the achievable pressure, while speed and geometry determine the flow rate. Key parameters are flow rate, pressure, viscosity, solids content, temperature, rotor and stator material and the shaft seal. Versions with a hopper and feed screw handle very viscous masses, for example in paper mills and sewage treatment plants.
The stator and rotor wear as a result of abrasion, swelling or dry running. Even brief dry running can destroy the stator, which is why dry-running protection is often used. For maintenance, it is worth monitoring the delivery rate and current consumption. Falling output at the same speed indicates stator wear early on, so the replacement can be planned rather than carried out after a breakdown.
In practice: maintenance and procurement
A replacement stator and rotor require the size, number of stages, rotor geometry, materials and, where applicable, undersize or oversize version. The stator, rotor and joint parts are classic items to keep in stock for critical pumps.
Synonyms and abbreviations: PC pump · eccentric screw pump · progressing cavity pump · helical rotor pump · single-screw pump
Frequently asked questions
What is a progressive cavity pump used for?
It pumps media that are too viscous, abrasive or rich in solids for centrifugal pumps, such as sludges in sewage treatment plants, coating colours in paper production, adhesives, resins and food masses. Thanks to the even, low-shear delivery, sensitive substances remain intact. It is also suitable for metering, because the flow rate is proportional to the speed.
Why is dry running dangerous for progressive cavity pumps?
The elastomer stator is lubricated and cooled by the pumped medium. If the pump runs dry, the stator heats up very quickly due to friction and can burn or stick. Even short periods of dry running cause damage. Dry-running protection with temperature or level monitoring switches the pump off in good time.
What information is needed for the stator and rotor of a progressive cavity pump?
Required are the pump type and size, number of stages, rotor material and any coating, stator elastomer, geometry and, where applicable, fit variant. This data is usually found in the type code or the order confirmation. The serial number helps with special versions. If the medium or temperature changes, the stator material must be reassessed.
How can you tell that a stator is worn?
Signs are a falling flow rate at the same speed, declining pressure build-up, rough running and rising current consumption. On dismantling, scoring, washed-out areas, swelling or hardening of the elastomer become visible. The rotor should then also be checked for wear and coating damage.