ISO 6358-2:2019

Overview

ISO 6358-2:2019 - "Pneumatic fluid power - Determination of flow-rate characteristics of components using compressible fluids - Part 2: Alternative test methods" - defines two alternative test methods (the discharge test and the charge test) for measuring the flow-rate characteristics of pneumatic components that handle compressible fluids (gases). The standard focuses on components with fixed or variable internal flow passages and specifies test installation, measurement procedures, data presentation and uncertainty evaluation. It is one part of the ISO 6358 series for pneumatic flow measurement.

Key topics and requirements

• Test methods: Discharge test and charge test as alternative methods to steady-state tests in ISO 6358-1.
• Measured parameters: Sonic conductance (C), critical back‑pressure ratio (b), subsonic index (m) and an additional pressure-related parameter (Δp) used together to represent choked and subsonic flow behavior.
• Stagnation-pressure measurement: Tests use upstream and downstream stagnation pressures to account for flow velocity effects.
• Test installation: Requirements for circuits, expanded inlet/outlet tubes to reduce inlet velocity assumptions, and an isothermal tank (including structure, stuffing and volume calibration).
• Applicability / exclusions: Not applicable to components with unstable/hysteretic flow coefficients, internal feedback devices (e.g., regulators), devices with cracking pressure (check or quick‑exhaust valves), or components that exchange energy with the fluid during measurement (e.g., cylinders, accumulators).
• Supporting information: Annexes cover measurement uncertainty (A), tank volume calibration (B), tank stuffing guidance (C), isothermal performance testing (D), formulae for calculations (E), and calculation procedures (F).

Applications and users

Who benefits from ISO 6358-2:2019:

• Manufacturers of pneumatic valves, flow control devices, connectors and manifolds - for product characterization and catalog ratings.
• Test laboratories and quality assurance teams - to perform repeatable, standardized flow measurements.
• R&D and design engineers - to model component behavior in systems and validate performance under compressible flow conditions.
• System integrators and specifiers - to compare components based on standardized flow parameters.

Practical advantages over ISO 6358-1:

• Lower required air-source capacity
• Easier testing of components with higher flow capacity
• Reduced energy consumption and test time
• Lower noise levels in charge tests

Related standards

• ISO 6358-1 - General rules and steady-state test methods (includes hysteresis testing).
• ISO 6358-3 - Methods to estimate assembly flow behavior from component characteristics.
• ISO 1219-1, ISO 5598 - Symbol and vocabulary references used in pneumatic standards.

Keywords: ISO 6358-2:2019, pneumatic fluid power, flow-rate characteristics, discharge test, charge test, compressible fluids, sonic conductance, critical back-pressure ratio, subsonic index, isothermal tank.