Overview
ISO 789-2:2018 specifies standardized test procedures to determine the lifting capacity of rear-mounted three-point linkage systems on agricultural tractors. It defines how to measure the maximum vertical force the tractor’s hydraulic lift can exert at the lower hitch points and at a point 610 mm behind the hitch on a coupled frame. The standard is intended for comparative, static testing of tractors (and can also be applied to front-mounted three‑point hitches), not for sizing implements.
Key topics and technical requirements
- Scope of measurement
- Maximum vertical force at the lower hitch points throughout the full range of movement.
- Maximum vertical force at a point 610 mm to the rear of the hitch on a frame attached to the linkage.
- Test method
- Apply a vertical, measurable external load and record lifting force and hydraulic pressure at a minimum of six points (including both extremes) across the lift range.
- Correct measured forces to a hydraulic pressure equal to 90% of the relief valve pressure; the lowest corrected value is reported as the maximum vertical force for the full range.
- Setup and adjustments
- Secure the unballasted tractor horizontally so tyres/suspension are not deflected.
- Adjust linkage according to ISO 730 power range and lower hitch point height; upper link length set so mast is vertical when lower links are horizontal.
- Throttle lever set fully open during tests.
- Environmental and hydraulic conditions
- Hydraulic fluid as recommended by manufacturer; temperature at test start 65 °C ± 5 °C (or state measured temperature if not achievable).
- Ambient temperature 23 °C ± 7 °C; atmospheric pressure should not be less than 96.6 kPa.
- Measurement units and tolerances
- Force, pressure, distance, rotational speed and other tolerances are specified (e.g., force ±1%, pressure ±2%).
- Reporting
- Test report must include tractor selection, running‑in, adjustments, measured values, any repairs and deviations.
Applications and who uses it
ISO 789-2 is used by:
- Tractor manufacturers for product development and performance validation.
- Independent test laboratories and certification bodies conducting comparative lifting-capacity tests.
- Agricultural OEMs and implement designers evaluating compatibility and comparative performance.
- Procurement teams and technical specifiers comparing tractor hydraulic lift performance.
Practical benefits include consistent, repeatable comparison of three-point linkage lifting capacity, improved product transparency, and harmonized testing across markets.
Related standards
- ISO 730 - Rear-mounted three‑point linkage categories (used for linkage setup).
- ISO 789-13 - Vocabulary and specimen test report (reporting format).
- ISO 3448 - Viscosity classification (hydraulic fluid identification).
Keywords: ISO 789-2, three-point linkage, lifting capacity, agricultural tractors, test procedures, rear three-point hitch, hydraulic lift, lifting force, tractor testing.
Open preview (PDF)Agricultural tractors — Test procedures — Part 2: Rear three-point linkage lifting capacity