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Rotary lobe pump needs 10 % less energy

Cost-effective conveyance
Rotary lobe pump needs 10 % less energy

Conveying systems represent a substantial cost factor, particularly in the chemical, food and pharmaceutical industries. In order to meet the growing pressure to achieve efficiency, Netzsch has developed the Tornado T2 rotary lobe pump. Conventional design principles were comprehensively reworked so as to reduce service times, increase operational reliability and lower both material and energy costs.

The author: Erwin Weber Manager of the Tornado rotary lobe pumps product line , Netzsch Pumpen & Systeme

Pumps in the processing industry must be stable under pressure as well as constant and smooth – while at the same time requiring only minimal maintenance with low operating costs. Positive displacement pumps have already proved their worth over a long period of time in a variety of fields. They achieve high pumping capacities, are self-priming and insensitive to dry-running, and convey without strong pulsation or shear forces. They are suited for media of any viscosity, which may simultaneously be abrasive, contain solids or gases and be lubricating or non-lubricating. It was essential to keep these typical characteristics when reworking the pump and to additionally increase its efficiency through design modifications.
Mix of materials saves energy
Reversing the materials in the pump chamber represents a crucial innovation. Instead of elastomer lobes rotating in a steel chamber, light hollow rotary lobes made of steel or stainless steel run in a housing lined with a specially shaped elastomer insert. The particular advantage of this is that the insert’s thin-walled rubber skin is less seriously affected by temperature fluctuations than the relatively thick rubber layer of the previous rubber lobes. This means that expansion and contraction are easier to control, enabling significantly narrower tolerances in the manufacture of the elastomer components. For a radial gap to actually develop, a far greater amount of elastomer would have to be worn away from the whole radial area of the insert than on the lobe tips of the former rubber lobe design. The clearances can therefore be reduced to the technically feasible minimum and the overall level of efficiency is improved.
In addition, it was ensured that only steel and rubber surfaces come into contact with one another at any time anywhere in the pump chamber. To achieve this, a precisely dimensioned elastomer insert was vulcanised onto the edges of the rotary lobes, so that there is not only hard-soft contact between the lobes and the housing during rotation but also on the surfaces of the lobes themselves. This structure reduces friction and thus power loss. The new design has succeeded in lowering energy consumption by around 10 % overall in comparison to previous models.
This mix of materials moreover means less wear and generally better preservation. Until now, the elastomer lobes have been exposed to strong dynamic forces when in operation, accelerating the ageing of the material. Steel, by contrast, is resistant to motion for a considerably longer time, leading to leaner costs for maintenance work and spare parts. Conversely, when signs of wear start to appear, the new elastomer housing insert can be replaced much more quickly and at a much lower cost than normal wear plates. The special geometry of this casing with its machined-in pockets also reduces pulsation, with the result that the Tornado T2 with straight bi-lobe rotors achieves similarly low pulsation values to complex spiral lobe designs. On top of this, the simpler and more robust lobe shape permits simple replacement of individual rotary lobes and gives a smaller backflow thanks to its longer sealing line. Fewer lobes equate to larger free-flow chambers in the pump, allowing a larger free ball passage. Fluids containing coarse solids can therefore be conveyed reliably with less wear.
Lower maintenance costs
With a view to minimising the maintenance and cleaning costs, the pump was designed in such a way that the whole front can be taken off to enable maximum free access for maintenance work. In addition, this design gets rid of most of the metal surfaces that come into contact with the product and consequently avoids corrosion problems.
The rotary lobes are attached with innovative taper lock ring sets outside the housing, so that they can be quickly dismantled without any special tools and refitted just as easily. An integrated positioning and installation gauge makes positioning far easier. Before fitting the rotary lobes, the preset mechanical seal cartridges are attached to the integrated casing, secured and pushed over the shaft together with the rotary lobes, thus saving even more time. The modular design of the seals also allows different cartridge types to be installed in a standard seal housing. The sliding surfaces of the shaft seals are free of any dead spaces, positioned flush with the rear of the lobes in the pump chamber and constantly rinsed by the conveyed fluid. There are likewise no dead spaces outside the flow area, where impurities could collect and cause seal damage. In the same way, the new attachment technology ensures that the rear surfaces of the rotary lobes remain smooth and do not provide any contact surfaces for fibres or solids. This not only prevents clogging or blocking; it also means that the pump can be cleaned manually or according to CIP principles without any complications.
In addition to the actual conveying elements, the rotary lobe pump’s drive was also redesigned, focusing on the costs for installation, operation, environmental production and lost production. To achieve this, the expensive timing gear which is prone to faults was replaced by a simple toothed belt that comes under the normal warranty cover. This belt, which has teeth on both sides, is used both for power transmission and to synchronise the rotary lobes. If a large solid body which cannot be conveyed were to get into the pump chamber, this would not automatically lead to the gearbox being damaged or the shaft broken, as would have been the case in the past, but in the worst case scenario simply to the belt jumping or rupturing. A ruptured toothed belt does not entail any kind of consequential damage such as the destruction of the timing gear, for example.
It was also possible to significantly reduce the provisioning of spare parts, which had previously often been very extensive, because the efficient structure of the belt drive only involves a small number of components and creates optimal robustness. The new drive also runs very smoothly and generates hardly any vibrations, noise or friction heat. The rotating components are generally better preserved and last longer. The toothed belt can be replaced quickly if necessary, simply by loosening two screws, resulting in substantially shorter downtimes compared to a complete gearbox overhaul. Furthermore, expensive oil changes throughout the service life are now a bygone thing because synchronisation takes place completely without oil. Leaks that harm the environment are ruled out from the outset.
The bearing housing is a fully encapsulated unit that is lubricated for life. Ingress of the conveyed fluid is prevented. The shaft diameter, manufacturing tolerances and bearing quality allow double-acting mechanical seals to be retrofitted as standard. All-metal pumps can be operated with very narrow clearances and a correspondingly high level of efficiency.
Special model for critical media
The slim design of the new Tornado T2 makes it far more compact and around 30 % lighter than comparable models and it can therefore be used for mobile applications with any problem.
It is suitable for sensitive foods such as edible oil as well as for aggressive chemicals like highly abrasive concrete primer, for example.
There is also an all-metal model for particularly challenging media. The all-metal pump is available in stainless steel or special steels and can additionally be coated, making it resistant to abrasive or chemically aggressive media as well as high temperatures.
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