Overview
ISO 15086-2:2025 - "Hydraulic fluid power - Determination of the fluid-borne noise characteristics of components and systems - Part 2" specifies a standardized procedure to measure the speed of sound in a fluid enclosed in a pipe using pressure transducers. Applicable to hydraulic circuits operating under steady-state conditions, the document covers pressure pulsations over a frequency range of 10 Hz to 3 kHz and supports accurate hydro-acoustic characterization of components and systems.
Key topics and technical requirements
- Measurement scope: Determination of fluid speed of sound from pressure-transducer signals mounted in a measurement pipe.
- Applicable systems: All hydraulic circuits under steady-state conditions regardless of size.
- Frequency range: Pressure pulsation analysis from 10 Hz to 3 kHz.
- Two measurement methods:
- Method 1 - Three-transducer method: Preferred for in‑system measurements under effective working conditions; can be performed alongside ISO 10767 and ISO 15086-3 hydro-acoustical tests.
- Method 2 - Antiresonance method: Uses acoustic antiresonance in a closed-end pipe to derive speed-of-sound data.
- Instrumentation requirements:
- Static instruments (mean flow, pressure, temperature) must meet industrial class (class C) accuracy.
- Dynamic pressure transducers: resonant frequency ≥ 30 kHz, linearity ±1%, acceleration compensation preferred.
- High-pass filtering allowed, provided amplitude/phase error ≤ 0.5% / 0.5°.
- Test rig & conditions: Guidance on thermal insulation, calibration of pressure transducers, control of fluid temperature, density, viscosity, mean pressure and (for Method 1) mean flow.
- Data and reporting: Required test-report items, data-reduction algorithms and example MATLAB routines are supplied in informative annexes.
- Measurement quality: Annexes define measurement error classes and dynamic/static accuracy expectations.
Applications and users
- Who uses it:
- Hydraulic test laboratories and acoustics labs
- Hydraulic component manufacturers (pumps, valves, actuators)
- System integrators and OEMs performing noise prediction or validation
- R&D engineers and consultants working on fluid-borne noise, vibration and harshness (NVH)
- Quality and compliance teams implementing ISO 15086 series
- Practical uses:
- Produce tables of speed-of-sound vs. pressure and temperature for specific fluids
- Improve hydro-acoustic models and noise predictions
- Validate and troubleshoot hydraulic systems where fluid-borne noise affects performance
- Ensure consistency when comparing component noise measurements across test rigs
Related standards
Keywords: ISO 15086-2:2025, speed of sound in fluid, hydraulic fluid power, pressure transducers, measurement pipe, fluid‑borne noise, three‑transducer method, antiresonance method, pressure pulsations.