Understanding Blowers: How to Make the Best Use of Blowers and Compressors

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TURCK GmbH

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Everest Blower Systems

How do Basic Twin Lobe Rotary Air Blowers Work?

Let us focus on twin lobe blowers, also popularly know as “Roots blowers”, based on the name of its inventors. Twin lobe rotary air blowers belong to the category of positive displacement blowers. They consist of a pair of involute profiled (shape of 8) lobes/rotors rotating inside an oval shaped casing, closed at ends by side plates. One lobe is the driving lobe, which is driven by the external power, while the driven lobe is driven by a pair of equal ratio gears.

Both lobes rotate at same speed but in opposite directions. As the rotors rotate, air is drawn into inlet side of the cylinder and forced out of the outlet side against the system pressure. With each revolution, four such volumes are displaced.

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Oil Free and Without Compression

The air, which is forced out, is not allowed to come back due to the small internal clearance within the internals of the machine, except a very small amount (SLIP). There is no change in the volume of the air within the machine, but it merely displaces the air from the suction end to the discharge end, against the discharge system resistance i.e., no compression takes place in the machine.

Since the lobes run within the casing with finite clearances, no internal lubrication is required. The air, thus, delivered is 100 per cent oil free. These blowers deliver, practically, a constant flow rate independent of the discharge pressure conditions. The flow rate is dependent, largely on the operating speed.

Due to these constructional features, it has the following distinct characteristics:

• Flow largely depends on operating speed.

• The input power is largely dependent on the total pressure across the machine.

• The suction and discharge pressures are determined by the system conditions.

• The temperature rise of the discharge air and machine largely depends on the ƒ¢p across it.

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