The rotary vane principle has been used for many years as the basis for numerous vacuum pumps and compressors. However, because wear occurs at the sliding surfaces, some maintenance is inevitable. Dynamic systems, however, such as radial and side channel blowers, have one major advantage: since there is no contact between the blades of the impeller and the working chambers in which air is trapped and centrifugally accelerated to produce pressure and/or vacuum, there is very little wear and practically no maintenance. Lack of mechanical contact in the side channel design also makes such designs inherently quieter.

Despite their advantages, developers at Rietschle embarked on a development programme to improve the efficiency of their side channel blowers by 25% and reduce weight by up to 30%. The first result of this research is a new design called Bora. The key feature of the product is a new impeller design. Available in double flow or double stage design, there are 13 different sizes of vacuum pumps and compressors, all fitted with a standard electric motor drive.

Now the systems builder can select a smaller size unit with lower power consumption while retaining the performance of earlier units. Take the example of a traditional side channel, 90m(3)/hr capacity compressor/vacuum pump, which presently requires a 0.55kW electric motor. The Bora 90 delivers the same performance with a 0.37kW rated motor.

Here is how it is done. Traditionally, side channel designs make use of a ring-shaped working chamber that has a circular cross section. One half of the cross section is formed by the impeller, with its radial blades on one side, while the other fixed half is formed by the housing. The impeller rotates in an anti-clockwise direction, drawing air in through the inlet, compressing it and passing the compressed air out through the outlet. The system works as a vacuum pump when throttled on the suction side and as a compressor when throttled on the pressure side.

While the new design follows the same principle of operation, the shape of the shovels that form the cross sectional half of the impeller have been modified. While previous designs sported a rectangular cross section, the shovels on the Bora are inclined, and it is this feature that has led to an increase efficiency and pressure. According to Heinrich Faller, a senior engineering manager at Rietschle in Schopfheim, there were some trade-offs between obtaining a higher efficiency and the noise of the blower. So while the new design is a lot more efficient than its predecessor, it is also slightly noisier.

The company has also taken the Bora product range and added an integral frequency controlled drive, creating what it calls the Blizzard. Developed between Rietschle and Integral Drive Systems, the frequency inverter is integrated with the motor fan cover for cooling. The new drive will be useful in variable frequency vacuum pump and blower applications, returning an energy saving of 20%.


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