ISO 6358-1:2013

Overview

ISO 6358-1:2013 - "Pneumatic fluid power - Determination of flow‑rate characteristics of components using compressible fluids - Part 1: General rules and test methods for steady‑state flow" - defines a steady‑state laboratory method to measure the flow‑rate characteristics of pneumatic components that use gases (compressible fluids). The standard specifies the required test installation, test procedures, and presentation of results, using stagnation pressure and temperature to characterise flow from choked to subsonic regimes.

Key topics and technical requirements

• Scope and exclusions: applies to components with fixed or variable internal flow paths; excludes components with unstable flow coefficients (marked hysteresis), internal feedback (e.g., regulators), or devices that exchange energy with the fluid during measurement (e.g., cylinders, accumulators).
• Flow parameters: defines and prioritizes four characteristic parameters used to represent flow behaviour:
  • C (sonic conductance) - conductance at choked (maximum) flow (defined using upstream stagnation conditions).
  • b (critical back‑pressure ratio) - boundary between choked and subsonic flow (based on downstream/upstream stagnation pressure ratio).
  • m (subsonic index) - refines subsonic flow modelling (≈0.5 for fixed bore components, variable otherwise).
  • Δp_c (cracking pressure) - for components that open with increasing upstream pressure (e.g., check valves).
• Test installation requirements: specifies circuits for constant and variable upstream pressure tests, pressure‑measuring tubes (expanded inlet/outlet to capture stagnation conditions), connectors, and general plumbing/layout constraints to meet flow theory assumptions.
• Measurement and analysis: procedures for steady‑state measurements, flowmeter calibration (Annex B), calculation of characteristics (Annex H provides guidance including example Excel Solver), and evaluation of measurement uncertainty (Annex C).
• Reporting: format and presentation of results, recommended units, and graphical/equation representations (Annex E, F). Annex G includes example results for commercial components.

Applications and practical value

• Compare and verify manufacturer flow data and datasheets.
• Size and select pneumatic valves, fittings, manifolds, hoses, and silencers based on measured conductance and flow behaviour.
• Provide verified input data for system modelling, simulation and performance prediction in pneumatic fluid power systems.
• Establish repeatable test methods for R&D, quality control, and component certification in test laboratories.
• Useful for OEMs, component manufacturers, test labs, system integrators, and standards/quality engineers.

Who should use this standard

• Pneumatic component manufacturers and test laboratories
• R&D and quality assurance engineers in fluid‑power and automation industries
• System designers and integrators requiring verified flow data for simulation and sizing

Related standards

• ISO 6358‑2 (alternative test methods)
• ISO 6358‑3 (assembly calculation, under preparation)
• Normative references cited: ISO 5598 (vocabulary), ISO 8778 (reference atmosphere), ISO 1219‑1 (symbols), ISO 16030 and ISO 14743 (connections)

Keywords: ISO 6358-1, pneumatic fluid power, flow-rate characteristics, compressible fluids, steady-state flow, sonic conductance, critical back-pressure ratio, flowmeter calibration, measurement uncertainty.