Comparing Regenerative and Centrifugal Blowers

Let's Define Each Blower.

What is a Regenerative Blower?

A regenerative blower has impeller blades passing the inlet port to draw air or other gases into the blower. The impeller blades use centrifugal action to accelerate the air outward and forward. Here the regenerative principle takes effect as the air is turned back by the annular shaped housing to the base of the following blades, where it is again hurled outward. Each regeneration imparts more pressure to the air. When the air reaches the stripper section — the part of the blower located between the inlet and the outlet in which the annulus is reduced in size to fit closely to the sides and tips of the impeller blades — the air is stripped from the impeller and diverted out of the blower. The pressures or vacuums generated by the one or two spinning, non-contacting oil-free impellers are equal to those obtained by many larger multi-stage or positive displacement blowers.

What is a Positive Displacement/Rotary Lobe Blower?

Unlike the blower described above, a positive displacement blower, also called a rotary lobe or PD compressor operates using the positive displacement principle. Two figure eight, precisely machined impell ers   are mounted on parallel shafts which are fastened together and turn in opposite directions . The two   shafts are held in synchronization by lubricated gears, attaching them together. The gears need to be continually submerged in a bath of oil or other lubricants — and sealed from air flow. Rotary lobe/positive displacement blowers can be used in applications requiring constant flows and pressures of 4-15 PSI.

What is a Rotary Vane Blower?

Rotary vane blowers are similar to PD blowers, but they can provide variable pressure at a constant flow. Most popular units have a series of four or more sliding vanes fitted into a rotor. The vanes will capture free air as the offset rotor passes the inlet port. As the rotor turns, the air is compressed by the decreasing space on the inlet. This compressed air is then forced out of the pressure port.

 

What is a Centrifugal Blower?

Centrifugal blowers are constant-displacement or constant-volume devices. This means that at a constant fan speed, a centrifugal blower moves a relatively constant volume of air. This design is normally found where a large flow is required with low pressure. Air enters the center of a rotary impeller in which there are a number of fixed vanes. Using centrifugal force, the air is directed outward where it is discharged.

What Performance is Available?

With all of these blowers, you must be thinking that they have similar performance levels, but this is not the case. In order to help you decide what blower is best for your application, it is helpful to know the approximate flow and pressure that you will need for your project. Don't forget to think about any system impedance that may change performance levels. Let's discuss the different performance levels for each type of blower.

Rotary vane blowers perform best for higher pressure levels (IWG) and low flow levels (CFM). Rotary lobe blowers with positive displacement are best for high pressure levels, but can also handle a large volume of air flow. When considering a blower with high pressure levels, remember to also think about mufflers and noise reduction techniques to help combat the high noise levels of these blowers. Adding silencers and mufflers may require you to readjust your needed performance level. However many blower manufacturers sell these add-on accessories when you purchase a blower.

On the other hand, centrifugal blowers can provide high flow while maintaining low pressure. They are a great choice if your application requires a large amount of air flow rather than high pressure. To maintain flow levels, these blowers run at top speed. As you can see in the performance levels chart (view chart here), centrifugal blowers can produce flows up to very large volumes. Please keep in mind that different manufacturers have different rates of flow for their blowers. (We're providing you with the most common flow and pressure for each type of blower discussed.)

Finally, regenerative blowers cover a wide range of performance levels due to their unique design. These blowers can efficiently and effectively work in most applications where you could use a rotary vane, PD or centrifugal blower. They also provide performance levels up to 250 IWG — and up to 1800 CFM. These blowers also are available with accessories specially designed for the blower, in case you need noise reduction or filtration for your application.

The chart referenced above shows the performance levels for each type of blower discussed. As you can see, not all of the blowers operate in the majority of performance levels.

What is the Cost of Ownership?

Cost of ownership can vary due to the maintenance required by the blower. Rotary vane, positive displacement and centrifugal blowers all require routine maintenance throughout the life of the blower. You may need to replace oil, filters, bearings or even vanes. It all depends on the type of blower you are purchasing. Regenerative blowers are virtually maintenance free due to their unique design. Unlike the other blowers, they don't use oil or have contacting parts, allowing them to last a very long time. 

They also have little to no issues with ingesting small foreign particles. Please keep in mind though, that depending on the size, some particles may cause the impellers to stop. If this occurs, you will need to dislodge all particles and double-check that the blower has no other particles in the system.

So, what's the real cost of ownership for each type of blower? While we may not provide exact prices since we'd have more than 1,000 different prices, we can provide an idea of what you'll be purchasing in regular intervals throughout the life of the system. Take a look at the different formulas below to help you decide upon the best solution for your application. Also, don't forget to take into account the performance levels we mentioned in the previous section. These could limit your choices and possibly increase the total cost of ownership.