ISO 18237:2017

Overview - ISO 18237:2017 (Hydraulic fluid dehydrator water separation testing)

ISO 18237:2017 specifies a repeatable laboratory method to evaluate the water separation performance of hydraulic fluid dehydrators. The standard defines the test circuit, apparatus, fluid preparation, sampling and analysis procedures so that dehydrator units can be compared on the same basis. It applies to dehydrators capable of drying a hydraulic fluid to less than 20% of the fluid’s water saturation level at the test temperature.

Key topics and technical requirements

• Test principle: circulate a defined volume of test fluid through a rig and dehydrator, heat to test temperature (50 °C), contaminate with water (typically to 3% by weight), emulsify, then run the dehydrator while monitoring water removal until the fluid is <20% saturation. Performance is reported as a three-part code.
• Test fluid: ISO VG 32 mineral oil conforming to L‑TSA (ISO 6743-5) is the reference fluid; procedures are provided for preparing and checking test fluid quality. Note: testing other hydraulic fluids (synthetic or fire‑resistant) may require modified starting water content.
• Apparatus essentials: reservoir with conical bottom (volume V ≈ 3 × dehydrator flow rate q in l/min), circulation pump (positive displacement, variable flow), in-line heater and temperature controller, thin-film capacitance water sensor, water mixer for emulsification, sampling valve per ISO 4021, glass sample bottles and Karl Fischer (KF) titrator for water analysis.
• Measurement accuracy and test conditions: examples of tolerances include volume ±3%, flow rate ±2%, test fluid temperature ±1 °C (target ±2 °C), environmental temperature 22–25 °C and relative humidity 55 ± 15% RH. KF reagent compatibility with the test fluid must be checked.
• Special considerations: fluids with high water solubility or zinc-based additives may require adjustments (e.g., higher initial water or modified KF analysis).

Applications - who uses ISO 18237:2017

• Manufacturers of hydraulic fluid dehydrators for product development and validated performance claims.
• Independent test laboratories performing comparative performance evaluations.
• Procurement and specification engineers who need objective criteria to select dehydrator equipment.
• Maintenance, reliability and contamination-control teams assessing dehydrator suitability for specific hydraulic systems and fluids.
• R&D teams testing dehydrator effectiveness across different hydraulic fluids and operating conditions.

Related standards

• ISO 760 - Karl Fischer water determination
• ISO 4021 - Sampling from operating systems
• ISO 1219-1 - Fluid power graphical symbols
• ISO 5598 - Fluid power vocabulary
• ISO 6743-5 - Lubricant classification (L‑TSA)

ISO 18237:2017 provides a rigorous, reproducible framework for evaluating dehydrator water-removal performance, enabling fair comparison and informed equipment selection for hydraulic fluid contamination control.