ISO 8573

Compressed Air Quality Classes ISO 8573

ISO 8573 sorts compressed air into quality classes for particles, water and oil. The standard gives each level of contamination a class number so user and supplier speak the same language. This guide explains the classes and shows how to choose the right treatment for your application.

5 minStand: 2026-07Geprüft: Pneumatics specialists

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3 classes

Particles, water and oil rated separately

+3 °C

Pressure dew point class 4 water

0.01 mg/m³

Residual oil content class 1 oil

Class 1-4

Typical range for industry

Inhalt

Structure
Classes
Selection
Frequently asked questions

How is ISO 8573 structured?

ISO 8573‑1 rates three types of contamination separately: solid particles, water and oil. Each gets its own class number, where a lower figure means cleaner air. A statement such as ISO 8573‑1:2010 [1:4:1] lists the particle class, the water class and the oil class in that order. This lets you define the required purity unambiguously, with no misunderstanding between operator and supplier.

The three classes are independent. A plant can supply very dry air (low water class) and still carry a high residual oil content if no activated-carbon filter is fitted.

What do the individual classes mean?

For each contaminant the standard defines several classes with clear limits. Water is usually stated as a pressure dew point, oil as a maximum total oil content in mg/m³ and particles as an allowed particle count per size band. The overview below shows common water and oil classes as a guide for sizing your treatment.

A lower class number means cleaner and drier air.
The pressure dew point must sit below the lowest ambient temperature of the line.
Class 0 is stricter than class 1 and is agreed individually between operator and supplier.

Which quality class does my application need?

The class you need depends on the application. Control air for valves and cylinders often works with mid-range classes, while painting, food contact or medical devices call for oil-free and very dry air. Choose the class for the most sensitive consumer in the system and size the treatment to match.

Control and working air

Valves and cylinders often accept water class 4 and oil class 3 to 4.

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Oil-free processes

Painting, food and medical devices need low oil and water classes.

Plan treatment

Check the sizing

With mixed consumers, size to the most sensitive point in the system.

Ask for advice

Fit dryers and filters in the right order: separate water and dry first, then set particle and activated-carbon filters. This keeps the required class stable over time.

Frequently asked questions

What does ISO 8573-1 [1:4:1] mean?

The three figures stand for particles, water and oil in that order. [1:4:1] means particle class 1, water class 4 with a pressure dew point of +3 °C and oil class 1 with no more than 0.01 mg/m³ residual oil.

Is class 0 better than class 1?

Yes. Class 0 is stricter than class 1 and is agreed individually between operator and supplier. The agreed limit must always sit below the class 1 value and be recorded on the datasheet.

Which class do I need for normal control air?

Valves and cylinders usually work with mid-range classes, such as water class 4 and oil class 3 to 4. Sensitive or oil-free processes need lower classes and matching treatment.

Define the right air quality

Our pneumatics specialists help you pick the ISO 8573 classes and the matching treatment for your application.

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Classified to standard

Classes to ISO 8573-1 clearly explained.

Clean and dry

Water and oil rated and sized separately.

Right order

Dryers and filters sensibly combined.

Expert advice

Pneumatics specialists support your selection.