Why You Need To Understand Proper Air Preparation

Particles, water and oils in compressed air reduce the service life and functionality of components and systems. They also impair productivity and energy efficiency. Being aware of how to achieve proper compressed air quality—and the filters which are needed to achieve the recommended air quality for common industrial applications—is critical to a well-run plant.

Air preparation

There are three variables to air preparation: compressed air purity, compressed air quantity (flow) and air pressure. Depending on the system requirements, coordinating these three variables ensures a high compressed air quality and forms the basis for selecting the proper service unit components.

The required compressed air purity increases both the running performance and the efficiency of pneumatic systems and can ensure compliance with legal specifications in industries, such as the food and beverage industry. The flow quantity is largely determined by flow cross sections and the design dimensions of the machine.

In general, provided the design is the same, larger components have higher flow rates. Optimized operating pressure increases the efficiency, minimizes wear and reduces power consumption. To coordinate the compressed air purity, compressed air quantity, and pressure for the specifications of a system, the correct individual components must be selected. These components include on-off valves, pressure build-up valves, pressure regulators, water separators, filters and drying units.

Why filtering is necessary

Atmospheric Air contains dust and dirt particles, not to mention considerable amounts of moisture in the form of humidity. The air produced by a compressor will be hot, wet and dirty. So the first step is to filter out these contaminants, starting with removing the moisture. This is typically achieved with a refrigerated dryer next to the compressor, which simply cools the air to just above freezing (~3˚ C) and removes the liquid that condenses.

If the contaminanats are not filtered out, trouble-free operation of the system components, like valves and cylinders, cannot be guaranteed in the long term. Poorly-prepared compressed air can cause seals to swell and wear prematurely, and contaminate control valves. As a result, the right compressed air preparation is essential for reducing machine downtime and idle periods, and for reducing maintenance and energy costs.

To help everyone communicate in the same language regarding air quality, international standard ISO 8573 was established in 2010 with definitions for compressed air quality. The air quality is defined with Class ratings for three types of contaminants: solid particles, water condensate content, and oil content. The Classes range from 1-9, with the lower numbers representing higher air purity. It specifies the maximum permissible levels of contamination and particle sizes for the respective quality classes. The Air Quality Class will help you identify what type of filter, or combination of filters, is needed.

Best Practices—filtration for common applications

Following are some common applications with the corresponding Air Quality Class, and the type of filtration.

Standard automation components such as valves and cylinders

• Quality Class 7.4.4—40 µm filter

Proportional valves, compact valves, pneumatic tools

• Quality Class 6.4.4—5 µm filter

Primary packaging, reduction of odors and oil vapors

• Quality Class 1.4.1—5, 1 and 0.01 µm, and active carbon filters

Semiconductor industry, pharmaceutical products

• Quality Class 1.3.1—5, 1 and 0.01 µm, and active carbon filters, membrane dryer

The required Air Quality Class or level of filtration is often defined by standard Industry guidelines or best practices. Most manufacturers of air preparation equipment can provide reference documentation that define the air quality requirements for different applications and industries. Once you have identified the ideal air purity class for the application, then choose the filters and dryers that are most appropriate. The following provides filter and dryer guidelines.