ISO 4392-2:2002

Overview - ISO 4392-2:2002 (Startability)

ISO 4392-2:2002 is the International Standard that defines test methods for determining the startability of rotary hydraulic motors used in hydraulic fluid power systems. The standard specifies two equivalent and comparable test methods - the constant torque method and the constant pressure method - to measure the pressure or torque at which a motor will reliably start under load. It also covers required test installation, instrumentation, measurement-accuracy classes, and mandatory test-report content.

Key topics and technical requirements

• Test methods: Two accepted procedures
  • Constant torque method - apply fixed opposing torque and increase inlet pressure until the motor starts.
  • Constant pressure method - maintain test pressure and reduce opposing torque until the motor starts.
• Equivalence: Results from the two methods are considered equivalent; no preference is given.
• Test installation:
  • Use an appropriate hydraulic test circuit (example illustrated in the standard).
  • Provide fluid-conditioning and filtration; maintain motor inlet temperature at 50 °C or 80 °C ± 2 °C.
  • Do not exceed motor manufacturer’s recommended maximum test pressure.
  • For bidirectional motors, perform tests in both directions.
• Instrumentation and accuracy:
  • Instruments must meet ISO 9110-1 and ISO 9110-2 requirements.
  • Measurement accuracy is classified into Classes A, B, and C (annex B).
• Data and results:
  • Determine start points from abrupt slope changes in angular-displacement vs. pressure/torque curves.
  • Calculate minimum starting efficiency from measured pressures, torques and swept volume (formulae provided in clauses 6.4 and 7.4).
• Test report: Must include motor description, method used, accuracy class, hydraulic circuit, fluid and viscosity (ISO 3448), fluid temperature, outlet pressure, swept volume, starting torques/pressures over a shaft revolution, minimum starting efficiency, and start direction.

Applications and who uses ISO 4392-2

• Hydraulic motor manufacturers - product development, performance claims, and quality control.
• Test laboratories and certification bodies - reproducible test procedures for compliance and comparison.
• OEMs and system designers - verifying motor start capability under expected loads (e.g., mobile machinery, industrial drives).
• R&D and maintenance teams - diagnosing startability issues, selecting motors for specific start-load conditions.

Note: special applications (e.g., winch drives) may be treated differently as indicated in the standard.

Related standards

• ISO 4392-1: At constant low speed and constant pressure (related part)
• ISO 4392-3: At constant flow and at constant torque (related part)
• Normative references: ISO 3448, ISO 4391, ISO 5598, ISO 9110-1, ISO 9110-2

Keywords: ISO 4392-2, startability, hydraulic motors, hydraulic fluid power, constant torque method, constant pressure method, startability test, test rig, starting torque, starting pressure.