Overview
ISO 20843:2011 specifies a laboratory test method for the determination of pH of fire‑resistant hydraulic fluids classified as HFAE, HFAS and HFC (per ISO 6743‑4). The standard describes sampling, measurement conditions and reporting rules used to monitor aqueous hydraulic fluids where pH variations may indicate contamination, bacterial proliferation or loss of corrosion protection.
Key topics and technical requirements
- Scope: pH measurement procedure for HFAE, HFAS and HFC fluids.
- Principle: measure potential difference between a glass electrode and a calomel reference (or use a grouped electrode device) with a pH meter at 20 °C.
- Sampling: obtain samples according to ISO 3170; measure as soon as possible, preferably within 48 hours to avoid oil release or pH change.
- Calibration: calibrate pH meter at 20 °C using suitable buffer solutions; choose buffers that bracket the expected pH.
- Required reagents:
- Water conforming to ISO 3696 Grade 2
- Buffer solutions (examples given at pH 7.00, 9.22, 11.72) - ready‑made buffers may be used
- Cleaning solvents: toluene and propan‑2‑ol
- Measurement procedure:
- Adjust sample to 20 °C ±1 °C, clean electrodes, immerse and read after ~1 minute stabilization.
- Avoid oil contact on the glass electrode surface (oil films can alter contact potential and cause errors).
- After testing, clean electrodes with toluene then propan‑2‑ol.
- Result expression: report pH to nearest 0.1 unit.
- Precision:
- Repeatability (r) = 0.2 for HFAE, HFAS, HFC
- Reproducibility (R) = 0.6 for HFAE/HFAS; 0.3 for HFC
- Test report must include reference to ISO 20843:2011, product identification (including water type and concentrate % for HFAE/HFAS), result, deviations from procedure and test date.
- Safety: standard warns of hazardous materials and requires users to apply appropriate safety practices.
Applications and users
ISO 20843:2011 is applied by:
- Test laboratories and quality control departments performing pH determination on fire‑resistant hydraulic fluids
- Hydraulic fluid manufacturers and formulators verifying product stability and corrosion protection
- Maintenance and reliability engineers monitoring in‑service fluids to detect microbial contamination or degradation
- Procurement/specification teams referencing pH acceptance criteria in technical specifications
Keywords: ISO 20843:2011, pH determination, fire‑resistant fluids, HFAE HFAS HFC, hydraulic fluids, pH meter, buffer solutions, ISO 6743‑4.
Related standards
- ISO 6743‑4 (classification of hydraulic fluids, Family H)
- ISO 3170 (sampling of petroleum liquids)
- ISO 3696 (water for analytical laboratory use)
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