The Fundamentals of Pneumatics
Part I - Pressure and Heat

This is the first in a series of in-depth articles covering the basic principles of pneumatics.

Controlled compressed air has been used for many years as a source of power in the field of automation. Within the sewing industry, pneumatics have been used to perform many functions including presser foot lifting, folder opening, thread trimming, chopping, and fabric positioning, to name a few. At the end of this series of articles you should have a better understanding of pneumatics and how it applies to the sewn products industry.

There are many reasons why an air system might be used on certain equipment. The following are just a few:

1. Properly conditioned air is clean and can be used to guide and move material or cool various machine components without staining or damaging sewn goods.
    
2. Air cylinders are capable of traveling greater distances with more power and speed control than electric solenoids.
    
3. It is very easy to add additional machines or components to a pneumatic system. To understand pneumatics it is first necessary to have a basic understanding of four important concepts and how they affect an air system. They are pressure, heat, humidity, and flow.

Pressure and heat will be reviewed in this article.

Pressure

Pressure is the force or push exerted upon a surface. Air consists of billions and billions of air molecules that are in constant motion. These air molecules are moving and constantly bouncing off of any surface they encounter. It is the sum of all these impacts on a surface added up together that equals pressure. For example, if we blow up a balloon, the balloon will expand and become inflated. The reason the balloon expands, see Figure 1, is because there are more air molecules bouncing off of the inside of the balloon than there are bouncing off of the outside of the balloon.

If we blow more air into the balloon as in Figure 2, there are even more air molecules bouncing off the inside of the balloon and the balloon gets even bigger. It is the constant smooth push of the air molecules bouncing off the inside surface of the balloon that creates a pressure on it. The balloon expands because the pressure pushing against the inside surface of the balloon is greater than the pressure pushing on its outside surface. It is important to remember that there are air molecules bouncing off the outside surface of the balloon as well.
 

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