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Vacuum pumps for conveying applications

21 November 2022

Uli Merkle discusses the different pneumatic pumps that are available for use in suction conveying applications for powder or granular materials. 

Pneumatic suction conveying is an important technology for feeding bulk goods gently through piping systems to the various process steps. In the area of food processing suction conveying is indispensable when powder or granular materials need to be transported. The choice of the vacuum generator will, essentially, determine the operating costs of a pneumatic conveying system. Modern vacuum technology today enables the economical and environmentally friendly operation of vacuum conveying systems.

In order to select the most effective method of vacuum generation, it is necessary to be become familiar with the operating conditions of the vacuum conveying system and to apply this knowledge when selecting the vacuum pump. These parameters are important in order to select the most suitable one from various principles for vacuum generation. 

On the one hand, the conveyed material and its properties must be known. Additional influential parameters are pipe routing, length and diameter as well as the type of conveying. These parameters can be used to determine the required differential pressure. The differential pressure and the volume flow are the main influential parameters for the technical selection of the vacuum pump or vacuum system. For the economic efficiency calculation, operating costs must be considered in addition to acquisition costs. This includes the energy consumption, possibly further acquisition costs for throttle regulation, valves or control depending on the vacuum generation, the operating time as well as the maintenance effort and costs.

Principles of vacuum generation
The following mechanical vacuum pumps, which achieve different differential pressures or vacuum levels, are mainly used for suction conveying – Side channel blowers; rotary lobe blowers; rotary vane vacuum pumps; and claw vacuum pumps.

Side channel blowers: Small side channel blowers can achieve high volume flows, making them suitable for use in short conveyor tracks and in flight conveying when low differential pressures and high volume flows are required. Side channel blowers compress oil-free and are relatively inexpensive to acquire. However, they do not have a stable characteristic curve so are not stable in volume. If they are operated at their performance limits, they have an above-average energy requirement.

Rotary lobe blowers: Rotary lobe blowers operate contact-free and thus without oil in the compression chamber. They can be used for differential pressures up to 500 hPa (mbar). Due to the relatively low differential pressure, the use of rotary lobe blowers in suction conveying is limited to applications requiring high volume flows at low differential pressures. In this area of application, rotary lobe blowers are characterised by their low power requirement. 

Rotary vane vacuum pumps: Rotary vane vacuum pumps can offer a suitable solution in suction conveying applications when high differential pressures are required and long conveyor tracks must be overcome. In addition, rotary vane vacuum pumps are always suitable when products must be conveyed slowly.

Ultimate pressures of up to 0.1 hPa (mbar) can be achieved with rotary vane vacuum pumps, which corresponds to a vacuum of 99.99 percent. No other vacuum generator in suction conveying achieves such a high vacuum and can also operate at lower differential pressures. This guarantees a stable characteristic curve over the entire pressure range from atmospheric pressure to operating pressure. Rotary vane vacuum pumps are lubricated with circulating oil, so they have an internal oil circuit, which does require regular maintenance.

Claw vacuum pumps: Claw vacuum pumps can offer an energy efficient solution. Busch’s claw vacuum are nearly maintenance-free and can be controlled on a demand-driven basis. Busch also offers individual central vacuum supply systems for several conveying systems or entire plants.

Vacuum for pneumatic suction conveying processes can be generated by various mechanical vacuum pumps. Which vacuum pump is the right choice will depend on the technical parameters of the conveying system. In the economic efficiency calculation, the acquisition costs for the vacuum generator and any further investments, the operating time and the maintenance effort or the resulting costs must be taken into account. 

Uli Merkle is global marketing manager at Busch Vacuum Solutions.

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