How the progressing cavity pump works

For process engineers considering the 'flow' of almost any material, the progressing cavity pump offers significant advantages. Here's how it works.

For process engineers considering the 'flow' of almost any material, the progressing cavity pump offers significant advantages.

The principle - a rotor (similar to a single start thread) turning inside a stator (similar to a twin start thread of the same profile) - produces a flow directly related to rpm, making the progressing cavity pump infinitely variable and easily matched to the requirements of a specific application.

The series of 'moving cavities' formed as the rotor turns inside the stator, produces a pumping action that requires no valves and is therefore particularly suitable for pumping viscous, highly particulate, abrasive or fragile structured products.

Progressing cavity pumps are also frequently used in applications requiring high suction lift.

Examples that illustrate the diversity of products that can be successfully pumped using progressing cavity pumps include cement slurries, sewage sludge up to 40% ds and even fish, where the combination of high suction lift and gentle pumping action is used to empty trawler holds.

The flow capability of the progressing cavity pump is primarily determined by the diameter of the rotor - a larger rotor produces larger cavities, increasing the capacity per revolution.

Using the NETZSCH NEMO range as an example, rotors vary from 5mm up to 180mm diameter producing flows that range from less than ½ litre per hour up to 550m³/hr.

Special pumps are also available, using micro rotors and stators, to produce flows small enough for automatic cake and confectionery decoration and the application of gasket sealant in continuous lines or in dots.

Different rotor forms, or geometries, are also available to determine the output of progressing cavity pumps.

'Standard' geometry rotors have a pitch roughly 5 times that of the rotor diameter.

However, the NETZSCH NEMO range includes two additional rotor forms.

'Long' geometry (where the pitch is roughly 10 times the rotor diameter) doubles the pumps capacity, but with an increase in pump length.

'Double' geometry (uses a standard pitch rotor that, instead of being a single-start rotor in a twin stator, is a two-start rotor in a three-start stator) increases the flow by nearly 50% with no increase in length.

Thus the progressing cavity pump incorporates many of the positive features of other types of pump.

Like the centrifugal pump it has no inlet or outlet valve.

Like the diaphragm pump it can deliver all types of materials.

Like the gear pump it can cope with high viscosities.

And, like piston, diaphragm, gear and screw pumps, it has a flow proportional to its speed of rotation, making it an ideal dosing pump.

In the processing industry the progressing cavity pump is able to deliver precise and continuous flow of even the most difficult materials.

Processing applications include food and beverages, dairy products, pharmaceuticals, paper and pulp and oil and petrochemicals.

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