compressed-air treatment

Select compressed-air treatment based on target quality

Compressed-air treatment is not just a matter of connecting individual devices to the compressor. The crucial question is what compressed-air quality is actually required at the point of use. Water, particles, and oil occur in various forms and must therefore be treated with different stages of purification.

The current product range allows for the combination of different quality levels. For many workshop and industrial applications, a system consisting of a condensate separator, appropriate filtration, and a refrigerated air dryer is sufficient. For more sensitive processes, significantly lower pressure dew points, finer filtration stages, and additional activated carbon adsorption may be required.

Pressure dew point: from approximately +3 °C to −40 °C

The pressure dew point describes how much compressed air can be cooled at operating pressure before the remaining water vapor condenses again. The lower the pressure dew point, the drier the compressed air.

The refrigerated air dryers in the product range are designed to achieve a pressure dew point of approximately +3 °C under their reference conditions. This is sufficient for many compressed air systems in temperature-controlled workshops and production facilities. As long as the downstream line remains above this pressure dew point under operating pressure, further condensation formation is largely prevented.

For applications involving cold outdoor piping, the risk of frost, or very high residual moisture requirements, desiccant air dryers with a pressure dew point as low as −40 °C are available. These allow the compressed air to be dried much more effectively than with a conventional refrigerated air dryer.

Targeted reduction of residual oil content

Oil can occur in compressed air as a liquid, an aerosol, or a gaseous vapor. Therefore, a single filter stage is not sufficient when particularly low residual oil levels are required. Coalescing and fine filters reduce liquid oil components and aerosols. For gaseous oil and hydrocarbon vapors, an activated carbon stage can then be used.

The separate activated carbon adsorber in the product line is specified to achieve a residual oil content of ≤ 0.003 mg/m³ under defined conditions. This value represents the performance of a properly designed treatment chain under the intended operating conditions. Pre-filtration, temperature, flow rate, and maintenance status influence the quality that can actually be achieved.

What does each DFF compressed air filter stage do?

DFF compressed-air filters feature a multi-stage design. This ensures that a fine filter does not have to handle the entire load of contaminants and aerosols in the raw compressed air. Upstream filters protect the finer stages, reduce their load, and allow for precise adjustment to the required compressed-air quality.

DFF-P – Coarse filtration up to 5 µm: The DFF-P is a robust pre-filter stage. It traps coarser solid particles and contaminants down to the specified filter fineness of 5 µm and serves primarily to reduce the load on downstream fine filters and dryers. This stage alone is not sufficient to ensure a high level of compressed air purity.

DFF-M – Microfiltration down to 0.1 µm: The DFF-M handles the separation of finer particles and aerosols. The specified filter fineness is 0.1 µm; the specified residual oil content is < 0.1 mg/m³. This stage is useful when fine oil and water aerosols, in addition to solid particles, need to be significantly reduced.

DFF-S – Fine filtration down to 0.01 µm: The DFF-S takes it one step further. With a specified filter fineness of 0.01 µm and a specified residual oil content of < 0.01 mg/m³, it is suitable for applications with significantly higher requirements for particle and aerosol purity. Appropriate prefiltration protects the very fine filter element from unnecessarily high loads.

DFF-A – Activated Carbon Final Stage: The DFF-A is not a standard particle filter stage. It is used after appropriate pre-filtration to further reduce residual oil and hydrocarbon vapors. At 20 °C, a residual oil content of < 0.005 mg/m³ is specified. It thus complements mechanical or coalescing filter stages in applications where particularly low-oil compressed air is required.

Not every compressed air system automatically requires all four stages. The appropriate filter combination depends on the quality of the incoming compressed air and the end-use application. For heavy-duty pneumatic tools, a simpler filtration system may suffice, while sensitive processes require multiple stages. It is also important to ensure correct sizing based on the actual flow rate and operating pressure; depending on the size, the DFF series covers flow rates from approximately 1.2 to 36.0 m³/min and is designed for pressures up to 16 bar.

Distinguish between the DFF-A and the separate activated carbon adsorber

The DFF-A is part of the modular DFF filter chain and is specified to achieve a residual oil content of < 0.005 mg/m³ at 20 °C. The separate activated carbon adsorber in the product line is a standalone treatment stage and achieves a residual oil content of up to ≤ 0.003 mg/m³ under defined conditions. Both solutions thus pursue a similar goal but are not technically equivalent.

Remove liquid condensate first

Cyclone separators are particularly well-suited for removing liquid condensate from the compressed air stream. The current series is specified to achieve a separation efficiency of over 99% for free liquid condensate. This stage significantly reduces the load on downstream filters and dryers.

However, the technical distinction is important: A cyclone separator removes liquid water droplets, but not water vapor. It therefore does not produce a defined pressure dew point and does not replace either refrigeration or desiccant air dryers.

Do not evaluate compressed-air quality based on a single value alone

In practice, several quality characteristics must always be considered together: residual particles, residual oil, and residual moisture or pressure dew point. For example, a compressed air system can be very dry yet still contain too many oil components. Conversely, very finely filtered compressed air may still have an excessively high water content.

Therefore, the treatment process should be planned from the consumer’s perspective: What particle size is still acceptable? What residual oil content is permissible? What pressure dew point is required? Only then can the appropriate combination of components be determined.

ISO 8573-1 as a Guide to Compressed-Air Quality

For industrial compressed air, quality is often described according to ISO 8573-1. Particles, water, and oil are evaluated separately. The achievable class is determined not by a single component, but by the entire treatment chain and actual operating conditions.

With the available filters, refrigeration and desiccant air dryers, activated carbon adsorbers, and condensate separators, different quality levels can be specifically achieved. Where a specific ISO class is required, the entire combination of flow rate, pressure, filter stages, pressure dew point, and residual oil target should be coordinated.

Compressed-Air Treatment for Industry and Professional Users

This category thus covers not only individual filters or dryers, but the entire technical chain—from the removal of free condensate through particle and aerosol filtration to drying and fine cleaning. This allows compressed air to be specifically tailored to applications in industry, workshops, blasting technology, and other professional processes.