# ANR — Atmosphère Normale de Référence

> Source: https://rodlesspneumatic.com/resource-center/pneumatic-glossary/anr/
> Language: en-US
> Category: Flow & valves

## Definition

Atmosphère Normale de Référence: Reference-air condition used by some pneumatic catalogs for normalized flow. Keep ANR values tied to the catalog's stated reference definition. Read the applicable product data and technical standard before treating a catalog value as interchangeable.

## Key facts

- **Term:** ANR
- **Full form:** Atmosphère Normale de Référence
- **Selection effect:** Keep ANR values tied to the catalog's stated reference definition.

## ANR: definition and engineering context

Atmosphère Normale de Référence. Reference-air condition used by some pneumatic catalogs for normalized flow.

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

## Why ANR affects pneumatic selection

Keep ANR values tied to the catalog's stated reference definition.

- Qn: Compare only when pressure conditions and measurement conventions match.
- ΔP: Available valve and line flow changes with pressure drop.
- Cv: Do not compare it directly with nominal NL/min without the fluid state and test conditions.
- Kv: Cv and Kv are related conventions but are not numerically identical.

## How to evaluate ANR 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.

- Nominal or normalized flow rate: Catalog flow value defined under a stated test condition.
- Pressure drop: Difference between upstream and downstream pressure.
- U.S. flow coefficient: A conventional coefficient describing flow capacity under a defined test basis.
- Metric flow coefficient: Metric coefficient convention commonly used for valve flow capacity.

## What to verify before selection

- Keep ANR values tied to the catalog's stated reference definition.
- Compare only when pressure conditions and measurement conventions match.
- Available valve and line flow changes with pressure drop.
- Do not compare it directly with nominal NL/min without the fluid state and test conditions.

## Common mistakes

- Treating ANR 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 ANR mean in pneumatics?

Atmosphère Normale de Référence. Reference-air condition used by some pneumatic catalogs for normalized flow.

### Why does ANR matter when selecting a component?

Keep ANR values tied to the catalog's stated reference definition.

### Can ANR 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 6358-1:2013](https://www.iso.org/standard/56612.html): Defines steady-state flow-rate testing and compressible-flow characteristics for pneumatic components.