All about Blowers Series: Impeller-based Blowers

​Although blowers are commonly used in manufacturing, it can be difficult to find good sources of information on the different types of blowers and how to choose the appropriate one. The purpose of this article series is to give a good, basic understanding of the different types of blowers and provide you with the technical information required to make a good decision for your application.

What are the different types of blowers?

​At its most basic level a blower is a tool that draws in air at an inlet and pushes air out as a steady stream at the outlet. Blowers can largely be classified into two categories: impeller based and positive displacement. Impeller based blowers have fins that radiate outwards from a rotating central axis. Positive displacement blowers use a mechanism of filling and emptying chambers at the inlet and outlet, respectively, to create flow. The fundamental difference between the two is that impeller based blowers have output flow that varies with pressure whereas positive displacement blowers have a more constant output flow regardless of change in pressure.

1. Impeller based blowers

​There are two main categories of impeller based blowers: centrifugal and regenerative. Each has different characteristics which lend themselves to different applications; but they both have output flow that vary greatly with changing operating pressure.

Centrifugal Blowers (also called a Centrifugal Fan, Squirrel Cage Fan, or Radial Blower)

Figure 1: Centrifugal blower Source: “Centrifugal fan” by EagleX is licensed under CC-BY-3.0.

Air enters at the center of a rotating impeller on which there are a number of fixed vanes. Through centrifugal action, air is forced to the periphery of the housing by the spinning impeller where it is discharged as a steady stream through the outlet. The negative pressure created at the centre hub, in turn, sucks in more air. Centrifugal blowers are not typically capable of producing high pressures and are best suited for applications requiring large volumes of air supplied at medium to low pressures.

Higher pressures can be obtained by increasing the impeller’s speed of rotation and through the use of specially designed impellers based on turbine technology. These blowers can have very high rates of rotation through the use of direct drive motors controlled via high frequency variable drives. High speed belt driven arrangements are another option. In both cases, these high speeds can reduce the expected life of the bearings. However, a direct drive system will be more energy efficient, as it eliminates the possibility of belt slippage, and it will put an end to maintenance costs associated with belt driven systems.

Alternatively, a multi-stage configuration can be used to generate higher pressures by having the air pass from the outlet of one blower to the inlet of another. They are generally quite large in order to accommodate several impellers, housings and a motor large enough to power multiple stages.

Multi-stage centrifugal blowers are normally used in large scale applications such as aeration in water treatment plants. For less onerous applications where a less substantial pressure increase is required two centrifugal blowers can be connected in series to emulate a two stage blower.
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Centrifugal blowers range in physical size from a cubic foot to the size of a small room with a correspondingly large range in volumetric output. Centrifugal blowers can be found with outputs anywhere from hundreds to hundreds of thousands of CFM.

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Regenerative Blowers (sometimes called side channel, lateral channel, or ring compressors)

Figure 2: Regenerative blower Source: STANMECH Technologies Inc.

Regenerative blowers have impellers that are constructed as a solid inside ring with vanes radiating outwards from its edges. Unlike centrifugal blower impellers, air enters from a side inlet, not through the centre of the impeller. As the impellor pushes the air around the ring, centrifugal forces cause the air trapped between the rotating impeller vanes to move towards the blower casing. The air flow is then forced to the base of a following impeller vane for recirculation in the same manner. This circular flow in combination with the revolution of the impeller causes air to follow a spiral path through a regenerative blower; the result is air that is under constant acceleration. This "regeneration" of air with each revolution allow regenerative blowers to develop significant pressure.

Regenerative blowers are able to operate at moderate speeds. Their direct drive construction reduces maintenance needs by eliminating the upkeep associated with belt- and gear-driven blowers.

Dual stage regenerative blowers are also available. In a single-impeller, two-stage unit, air makes one revolution around the front side of the impeller then, instead of being discharged, the air is channeled to make a second revolution before exiting the blower through the outlet. Other two-stage configurations are also available, including designs that use two separate impellers in one housing or two impellers and housings. Because regenerative blowers naturally produce higher pressures, they do not usually require multi-stages in the same way as centrifugal blowers. Two stage units are somewhat common, while more than two stages is rare.

For more information about the differences between Centrifugal and Regenerative blowers we recommend our article on the subject.
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The next article in this series will cover Positive Displacement Blowers. 

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