What is an air preparation unit?

Pneumatic systems work on compressed air. A medium that transmits power to, for example, cylinders, grippers and valves, which can then perform their task. For example, gripping a product, creating a linear displacement or developing a holding force. The quality of the compressed air largely determines the performance of the pneumatic system. Among other things, in terms of efficiency, effectiveness, safety, reliability, accuracy and speed. It is therefore important for practically every industrial pneumatic system that the compressed air used is of the correct quality. In this blog we will explain the role that the air preparation unit plays.

An air preparation has two functions:

1. Bringing and keeping the quality of the compressed air at the desired level

2. The (central) pressure control of the machine

This means that an air preparation unit can literally be seen as the heart of a well-functioning pneumatic system. But what do these two main tasks actually mean?

First function of air conditioning: maintaining compressed air quality

Pure compressed air consists only of pure air molecules. That means around 1% argon, 21% oxygen and the vast majority (78%) nitrogen. In practice, however, the air around us is quite polluted. The main types of pollution, which also adversely affect the functioning of a pneumatic system, are moisture and micro dust, soot and oil particles.

When air is compressed, these contaminants are also compressed. They then flow with the compressed air to the pneumatic components, where they can cause unnecessary problems. Especially the solid particles can lead to wear and damage, whilst moisture can cause corrosion but also promote the growth of micro-organisms. In the worst case, excessive fouling leads sooner or later to shutdowns. In less serious cases, they adversely affect performance: system efficiency is reduced, accuracy disappears, and energy consumption increases. All in all, this leads to unreliable machine operation, lower availability and, ultimately, higher maintenance costs.

Compressed air quality is described in the ISO 8573-1:2010 standard. The first part of the standard defines the quality of compressed air in terms of the maximum dust particles, water and oil content that may be present in the air. In addition, the standard defines the quality classes of compressed air with regard to:

  • Number and size of solid particles per volume
  • Moisture content / pressure dew point per volume
  • Oil content per volume

On the basis of these three types of pollution in the compressed air, the quality can be classified according to the table below. Each of the three pollutants listed above is given its own value in the designation. For example, the minimum requirement specified by Festo for standard applications is [7:4:4]. Here the first digit refers to the class for particle size and the quantity of particles per unit volume ([7] = 5to 10 mg/Nm3), the second digit to the moisture content ([4] ≤ 3 ˚C pressure dew point ) and the third digit to the oil content (=≤ 5 mg/Nm3).

Second air supply function: central control of the machine

The second core function of air supply is the (central) control of a machine or component. Examples of this are:

Central regulation of the desired compressed air working pressure

  • Realisation of switch-on and switch-off functions
  • Carry out central measurements using integrated pressure or flow sensors
  • Controlling certified safety valves at various safety levels.

Modular design

In order to achieve the desired compressed air quality and to be able to control the machine reliably and precisely, the air supply must consist of specific components. Festo has therefore designed its air supply units to be modular. This makes it possible to combine all the necessary components with each other and, if necessary, to replace or exchange them according to therequirements of the application or the environment, even when these change. In this way , all functions can be built in a compact way in one place within a machine.

In a next blog - in which the composition of an air conditioning system will be discussed - we will elaborate on this.

July 2022