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What is the Difference between a Turbo Blower and a Positive Displacement Blower?

To understand the difference between a Turbo Blower and a Positive Displacement Blower, we must first establish some core concepts.

A Turbo Blower is also sometimes referred to as a turbine blower. It is designed to compress air using an impeller rotating at very high speeds. Although centrifugal blowers can also “generally” be classified as a turbo blowers, we are more specifically interested in turbo blowers that are capable of delivering high flow rates and high differential pressures.

These turbo blowers have been designed and manufactured with some key components:

  1. air bearings
  2. precision machined impeller,
  3. high-speed and high-efficiency Permanent Magnet Synchronous Motors (PMSM) which are super high-speed motors capable of rotating at speeds of up to 20,000-rpm (instead of the more traditional induction motors that are classified as 2-pole (3600-rpm) or 4-pole (1800-rpm) electrical motors).

A Lobe Blower, also commonly known as a Roots Blower or Positive Displacement Blower, are blowers that date back to the 1860s invented by the Roots brothers. Today, there are both Twin Lobe and Tri Lobe Blowers available in the market.

These rotary-type positive-displacement blowers incorporate two rotors mounted on parallel shafts. In a twin-lobe compressor, each rotor has two lobes (four per compressor). In a tri-lobe machine each rotor has three lobes (six per compressor). The two rotors rotate in opposite directions.

As each rotor passes the blower inlet, it traps a definite volume of gas (the ‘displaced volume’) and carries it around the case to the blower outlet. With constant speed operation, the displaced volume remains approximately the same at different inlet temperatures, inlet pressures and discharge pressures. As each rotor passes the blower outlet the gas is compressed to the system pressure there and expelled. Small but definite clearances allow operation without lubrication being required inside the air casing. Timing gears control the relative position of the rotors to each other.

Which Blower is Better?

To determine which blower is better to use is a great question. Application Specialists believe that it all depends on the type of the application, and of course the operating system requirements.

The following chart is a fairly accurate comparison of the three (3) primary types of blowers.

Comparison of Efficiency of Types of Blowers

 

 

Lobe Blower

Multistage Blower

Turbo Blower

Working Principle

Volumetric

Centrifugal

Centrifugal Turbo

Power Transmission

V-Belt

Booster/Gear

Direct Driven

Flow Rate

1740-m3/hr

1740-m3/hr

1740-m3/hr

Flow Rate

1024-cfm

1024-cfm

1024-cfm

Discharge Press.

6500-mmwc(g)

6500-mmwc(g)

6500-mmwc(g)

Discharge Press.

9.25-psi(g)

9.25-psi(g)

9.25-psi(g)

Power

55-kW

48-kW

35-kW

Noise (@1-m)

85-110-dbA

90-100-dbA

75-80-dbA

Cost Basis

$$$

$$$$

$$$$

 

In summary, there is no one type of blower that fits all applications. In fact, there are numerous considerations that need to be considered when selecting the correct blower for its respective application.

It is for this exact reason that a “lowest cost solution” may not be the best way to proceed with equipment procurement. Instead, it is suggested that Design Engineers, Project Engineers, and the Procurement Department engage in active discussion with Application Engineers in determining recommendations for the most appropriate type of blower for any given application.

Contact us if you have questions about your application.

 

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Difference between a Turbo and Positive Displacement Blower