ISO 6953-3:2012

Overview

ISO 6953-3:2012 - "Pneumatic fluid power - Compressed air pressure regulators and filter‑regulators - Part 3" specifies alternative test methods for measuring the flow‑rate characteristics of pressure regulators using an isothermal tank instead of a flow meter. It applies to the decreasing flow‑rate portion of the hysteresis curve for both forward flow and relief flow, and is intended for components whose pressure‑regulation dynamics are fast (negligible during charge/discharge) and that do not exhibit overshoot or oscillation.

Key topics and requirements

• Scope and applicability: Tests apply to compressed air pressure regulators and filter‑regulators (ISO 6953‑1), electro‑pneumatic pressure control valves (ISO 10094), and other devices such as relief valves.
• Alternative method principle: Flow is inferred from pressure/temperature changes in an isothermal tank during charge (forward flow) and discharge (relief flow) cycles rather than direct volumetric flow measurement.
• Test installation: Standardized test circuit with compressed gas source, adjustable regulator, solenoid valves, isothermal tank(s), pressure transducers and digital recorder. Specific components and sonic conductance ratios are defined to ensure valid results.
• Test procedure: Requirements for setup, steady‑state preconditioning, sequence for charge and discharge tests, and conditions under which data are valid (no overshoot/oscillation).
• Measurement and accuracy: The standard specifies measurement accuracy and allowed test condition variation (examples: inlet pressure held within ±1 %; temperature measurement accuracy ±1 K; timing and volume accuracy requirements).
• Data processing and presentation: Methods for calculating flow‑rate characteristics, examples of test results, data‑processing techniques and visualization procedures. Annexes include illustrative examples and guidance on overshoot/undershoot effects.
• Limitations: Applicable only when the regulator’s dynamic response is sufficiently rapid and stable; otherwise ISO 6953‑2 (pressure‑regulation characteristics) should be used.

Applications and users

• Who uses it: Test laboratories, pneumatic component manufacturers, R&D teams, QA/validation engineers, and certification bodies working with compressed air pressure regulators, filter‑regulators and electro‑pneumatic control valves.
• Practical value:
  • Enables accurate flow‑rate characterization without large flow sources or expensive flow meters.
  • Reduces air consumption and shortens test time for high‑capacity components.
  • Facilitates standard, repeatable reporting of forward and relief flow characteristics for supplier literature and product marking.

Related standards

• ISO 6953‑1 - Main characteristics and marking for compressed air regulators
• ISO 6953‑2 - Test methods for pressure‑regulation characteristics
• ISO 6358‑1 / ISO 6358‑2 - Flow‑rate determination and isothermal tank requirements
• ISO 10094 / ISO 10094‑2 - Electro‑pneumatic pressure control valves
• ISO 5598 - Fluid power vocabulary

Keywords: ISO 6953-3:2012, pneumatic fluid power, compressed air pressure regulators, filter‑regulators, isothermal tank, alternative test methods, flow‑rate characteristics, electro‑pneumatic valves.