All about Blowers Series: Specialty 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.
​
Recommended Reading

• Part 1: Impeller-based Blowers
• Regenerative versus Centrifugal Blowers
• Part 2: Positive Displacement Blowers
• Part 3: Blower Comparison Chart
• Flow, Velocity, and Pressure

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 less affected by changes in operating pressure.

Specialty Blowers

​When an environment is unusually harsh—such as explosive, corrosive, or hot environments—a normal blower design must be adapted in order to operate safely. 

Explosive Applications

There are two aspects of specifying a blower for use in a potentially explosive environment. The first refers to an explosive gas passing through the blowers and concentrates largely on the materials and construction used for the areas the gas may contact. This is governed by the Air Movement and Control Association’s (AMCA) Standard 99-0401 – “Classification for Spark Resistant Construction.” There are three levels of construction—A, B, and C—as defined below:

• Type C: The blower is designed so that if the impeller or shaft comes loose and shifts during operation, two ferrous parts will not come into contact.
• Type B: The blower requires a non-ferrous impeller and a non-ferrous rubbing ring around the shaft hole. Extra locking systems are required to prevent the fan impeller, shaft, and bearings from shifting.
• Type A: The blower requires a non-ferrous airstream. Extra locking systems are required to prevent the fan impeller, shaft, and bearings from shifting.

Typically, blower manufacturers choose aluminum as the non-ferrous material for blower construction.

The second aspect of specifying a blower for an explosive application relates to the blower motor. Explosion proof motors are a class of electric motors that are constructed to both contain an explosion if it occurs within the motor as well as prevent the release of explosive gases or vapors to the surrounding environment. They are designed to ensure they are not the source of ignition in a potentially explosive environment. There are different sets of standards that govern explosion ratings of motors relating to the type of explosive hazard in the environment:

• CLASS I: Gases, vapors, and liquids
  • Group A: Acetylene
  • Group B: Hydrogen, etc.
  • Group C: Ether, etc.
  • Group D: Hydrocarbons, fuels, solvents, etc.
  • Division 1: Normally explosive and hazardous
  • Division 2: Not normally present in an explosive concentration (but may accidentally exist)
• CLASS II: Dusts
  • Group E: Metal dusts (conductive and explosive)
  • Group F: Carbon dusts (some are conductive and all are explosive)
  • Group G: Flour, starch, grain, combustible plastic or chemical dust (explosive)
  • Division 1: Ignitable quantities of dust normally are or may be in suspension, or conductive dust may be present
    
  • Division 2: Dust not normally suspended in an ignitable concentration (but may accidentally exist). Dust layers are present.
• CLASS III: Fibers
  • Textiles, wood-working, etc. (easily ignitable, but not likely to be explosive)
  • Division 1: Handled or used in manufacturing
  • Division 2: Stored or handled in storage (exclusive of manufacturing)

Published by Ohio Electric Motors.

When specifying a blower you must know the Class, Type, and Division of the environment you are dealing with. Blower manufacturers will be able to recommend the appropriate blower but will not be able to tell you what sort of environment you have.

High Temperature Applications

Standard blowers are meant to operate at or near ambient temperatures. Inlet temperatures above 60°C can cause damage, usually due to the operating limits of elements such as lubricating grease and bearings. Some regenerative blowers make use of high temperature lubricants and insulated motors which can raise the specified maximum operating temperature up to 140°C. It is important to note that the air will be compressed as it passes through the blower which will naturally raise its temperature. It is common for the air to increase 20-40°C (or more, depending on operating pressure) as it passes through a blower, this must be factored in when determining the operating temperature.
​
Recirculating blowers are often used for heated air applications to improve energy efficiency. Air that would be exhausted from the system is instead captured and fed back into the inlet of the blower. This lowers the energy requirement to reheat the air back to the system’s target temperature. Blowers designed for recirculating hot air have the bearing and motors insulated/isolated from the hot air stream. It is typical to see centrifugal blowers used for recirculating since their design lends to easier isolation. Common high temperature centrifugal fans can intake air in the range of 300°C.
 
The next article in our series discusses blower choice and the parameters that are important to consider when specifying a blower for your application.