Design progression for cavity pumps

Dean Palmer looks at a progressive cavity pump that has 70% fewer component parts and a new maintenance-free drive chain



A pump for handling difficult fluids has recently been subjected to a design and performance makeover - resulting in a more reliable product with 70% fewer parts.

Netzsch Pumps' Nemo M. Champ range of progressive cavity pumps has just nine major components, a 70% reduction compared to conventional pumps of this type. The units also incorporate a built-in reserve stator and maintenance-free drive chain, resulting in a more reliable pump with a longer operating life.

The patented stator section of the pump has a bonded elastomer lining of 'Nemolast', which provides the progressing cavity movement of the conveyed media under the action of the rotor. These stators are also reversible thanks to a quick clamping system, to provide an integrated reserve stator for extended operational life.

Optional elastomer linings are also available to suit a wide range of chemical or other aggressive media. Integrated gaskets and flow tapers at both ends ensure low NPSH values in both pumping directions. The stator clamping device also carries an information plate for pump maintenance and operational safety.

Nemo pumps belong to the rotating positive displacement group of pumps. The main components of this progressive cavity pump system, invented by Professor René Moineau in 1939, are a rotating part called the rotor and a stationary part referred to as the stator.

The rotor has a single helix shape and is normally made of metal. The stator is formed as a double-helix with twice the pitch of the rotor and is normally an elastomer.

The interference (compression) fit between the rotor and the stator creates a series of sealed chambers called cavities. When the rotor turns inside the stator, the pumping media moves continuously from the inlet to the outlet of the cavities, producing continuous delivery.

The stator tolerance is manufactured to seal both components, so no suction or non-return valves are required.

Five pumps are available in the range, suitable for use with low to high viscosity fluids - even solids - providing capacities up to 85m3/h (360gpm), at pressures of up to 6 bar (85 psi).

The pumps can handle treated and untreated sludge, grease and oil emulsions, industrial effluent and even processed food products. As well as environmental and waste water treatment applications, the pump's liquid handling capabilities make it suitable for chemical, general engineering, mining and quarrying, processing and vegetable washing plants.

The main benefits of the new range appear to be its compactness and performance over conventional versions. Pump capacity is proportional to rotational speed, with reversible flow direction. High suction and pressure capacities are combined with continuous low pulsation conveyance, independent of media pressure or viscosity. Maintenance and wear-free operation, with relatively low lifecycle costs and ease of servicing, are also key advantages.

A robust, space saving, bevel geared drive is used to power the chromium-plated rotor, connected via a corrosion-resistant flexible-rod drive chain. This rotating mechanism has no rotary joints or parts that wear and does not require lubrication. It can be removed easily if necessary.

The housing of the pump is compact, which helps prevent solids sedimentation, and it has diametrically opposed horizontal flanged ports for pipeline connection. One of these ports is fitted with a blanking plate and used for inspection or cleaning access.

The pumps are offered with a wide range of electric motor speed, power and supply voltage options, specified to suit a variety of applications.

Pointers

* The pumps were designed to be compact and have 70% fewer parts compared to conventional designs
* The unique stator section uses a bonded elastomer lining of 'Nemolast'
* Applications include most difficult materials, such as chemicals, food processing, mining and quarrying, general engineering and waste water treatment

Author
Tom Shelley

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