# ISO class — ISO 8573-1 purity class

> Source: https://rodlesspneumatic.com/resource-center/pneumatic-glossary/iso-class/
> Language: en-US
> Category: Air preparation

## Definition

ISO 8573-1 purity class: Three-part compressed-air cleanliness statement for particles, water, and oil. Specify every position and the measurement point. Read the applicable product data and technical standard before treating a catalog value as interchangeable.

## Key facts

- **Term:** ISO class
- **Full form:** ISO 8573-1 purity class
- **Selection effect:** Specify every position and the measurement point.

## ISO class: definition and engineering context

ISO 8573-1 purity class. Three-part compressed-air cleanliness statement for particles, water, and oil.

The term belongs to the air preparation context. Its exact limits can depend on the cited standard, catalog convention, unit system, reference state, and component configuration.

## Why ISO class affects pneumatic selection

Specify every position and the measurement point.

- Droop: Size the regulator from its flow curve, not port size alone.
- FR: Confirm drain type, filtration rating, relieving function, and flow curve.
- FRL: Select filtration, pressure range, drain, bowl, flow, and lubrication based on the application.
- PDP: Choose dryer performance below the lowest relevant system temperature.

## How to evaluate ISO class in a catalog or replacement project

Read the value together with its unit, test basis, operating pressure, temperature, circuit state, and manufacturer definition.

For replacement work, compare the complete datasheet and drawing. A matching abbreviation or nominal size does not by itself prove functional or dimensional interchangeability.

- Regulator pressure droop: Reduction in downstream pressure as flow demand increases.
- Filter regulator: Combined particulate filter and pressure regulator.
- Filter, regulator, lubricator: Combined compressed-air preparation assembly.
- Pressure dew point: Temperature at which water vapor condenses at the stated pressure.

## What to verify before selection

- Specify every position and the measurement point.
- Size the regulator from its flow curve, not port size alone.
- Confirm drain type, filtration rating, relieving function, and flow curve.
- Select filtration, pressure range, drain, bowl, flow, and lubrication based on the application.

## Common mistakes

- Treating ISO class as a universal definition without checking the manufacturer or standard context
- Mixing gauge and absolute values, incompatible units, or different reference conditions in one comparison
- Selecting a component from the term or nominal value alone without checking the complete operating point and drawing

## Frequently asked questions

### What does ISO class mean in pneumatics?

ISO 8573-1 purity class. Three-part compressed-air cleanliness statement for particles, water, and oil.

### Why does ISO class matter when selecting a component?

Specify every position and the measurement point.

### Can ISO class values be compared directly between catalogs?

Only after the unit, reference condition, test method, operating point, and manufacturer definition have been reconciled.

## Technical references

- [ISO 5598:2020](https://www.iso.org/standard/67985.html): Provides the international fluid-power vocabulary used to interpret pneumatic terminology.
- [ISO 8573-1:2010](https://www.iso.org/standard/46418.html): Defines compressed-air purity classes for particles, water, and oil.