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.
Blower Choice: What are the important design parameters?
1. Understand your Requirements
The first step in blower selection is to understand the application requirements. Below are some of the questions you should ask yourself:
These types of questions should narrow the focus to one or two types of blowers. As with any engineering problem, there is not always a single solution and there can be some overlap in the characteristics of two different blowers. For a refresher on the most common types of blowers available, see Part 1: Impeller-based Blowers and Part 2: Positive Displacement Blowers.
2. Determine Necessary Capacity of the Blower
The next step is determining the necessary capacity of the blower. Typically, a blower manufacturer will give you a table that includes maximum operating pressure and maximum volumetric air flow along with dimensions and various other specifications.
For a positive displacement blowers used in a pressure application, the flow is relatively independent of back pressure (to a limit) and they may have quite a large range of operating pressures.
Impeller blowers have a blower curve where the volumetric flow rate changes much more drastically with the operating pressure. The manufacturer supplied table gives maximum pressure and flow values but does not tell the whole story. The blower curve gives the specific relationship between operating pressure and the volumetric air flow generated by the blower. Where the curve meets the x-axis is the maximum output flow of the blower (typically only seen in application when it is exhausting to atmosphere). As the pressure increases due to factors such as hose/pipe attached to the outlet and inline components such as heaters/air knives/nozzles, the flow drops according to the relationship given by the blower curve. The point at which the blower curve meets the y-axis represents the pressure at which there is zero air flow from the blower. However, in larger blowers it is common that the maximum pressure rating for the blower will be exceeded before this point is reached. For more information, see our articles on How to Interpret a Blower/Fan Curve, Understanding Blowers as part of a System, and Flow, Velocity, and Pressure.
As a general rule, the operating pressure of the application should not be on the border of the maximum pressure rating of the blower. This can risk a zero flow condition which may risk damage to downstream components or it may risk damaging the blower due to overheating. In order to avoid over-pressure related damage, an over-pressure relief valve should be a consideration.
The next and last article in this series discusses three blower selection examples and walks through the thought process in the blower selection for each.