ISO 4392-1:2002

Overview - ISO 4392-1:2002 (Hydraulic fluid power, low speed testing)

ISO 4392-1:2002 specifies a laboratory method for determining the low‑speed characteristics of positive displacement rotary hydraulic motors (fixed or variable displacement). The standard describes a test circuit, required instrumentation and data acquisition, pretest calculations, controlled test conditions, and the procedures and calculations used to derive key performance metrics such as flow, volumetric efficiency and torque characteristics at constant low speed and constant pressure.

Keywords: ISO 4392-1, hydraulic motor testing, hydraulic fluid power, low speed characteristics, positive displacement rotary motors.

Key topics and technical requirements

• Scope and motor types: Applies to fixed and variable displacement positive‑displacement rotary motors tested at slow speeds where frequency effects influence steady torque output.
• Test installation and circuit: Defines a typical hydraulic test circuit (supply, relief valves, fluid conditioning, cooler/heater, constant‑speed load) and safety considerations.
• Instrumentation: Requires measurement of total flow, inlet/outlet pressure and temperature, inlet flow option, output torque, shaft speed and angular displacement. Instruments must meet ISO 9110‑1/2 requirements and resolve signals at frequencies >10× the highest expected fundamental frequency.
• Pretest calculations: Guidance for calculating rated geometric torque, displacement pulses per revolution, fundamental data frequency, and ideal flow at rated speed.
• Controlled test conditions: Typical conditions include inlet fluid temperatures (50 °C or 80 °C), inlet pressures at 100% and 50% of rated pressure, constant back‑pressure per manufacturer limits, minimum recommended slow speed (or 1 min‑1 if unspecified), and defined displacement settings for variable motors.
• Test procedure and tolerances: Maintain inlet/outlet pressure to ±2% or 1 bar (whichever greater), shaft speed ±2%, inlet temperature ±2 °C during recordings; establish thermal equilibrium; record enough revolutions to capture one complete motor cycle.
• Data analysis and results: Prescribes computation of derived swept volume flow, mean flow, flow irregularity, flow irregularity index, volumetric efficiency, peak‑to‑peak flow, mean torque, torque irregularity and torque irregularity index.
• Measurement accuracy: Defines three accuracy classes (A, B, C) in normative Annex A.

Applications and users

ISO 4392-1 is used by:

• Test laboratories and OEM quality/control teams performing hydraulic motor testing
• R&D and validation engineers evaluating low‑speed performance, torque irregularity and volumetric efficiency
• System designers and integrators assessing motor behavior under frequencies that affect connected systems
• Procurement and certification bodies requiring standardized performance data for positive displacement motors

Practical benefits: consistent comparative data, repeatable test methodology, and clear reporting formats for motor selection, troubleshooting and system integration.

Related standards

• ISO 4392-2 (Startability) and ISO 4392-3 (Constant flow and constant torque) - other parts of ISO 4392 series
• Normative references cited: ISO 3448, ISO 4391, ISO 5598, ISO 9110‑1, ISO 9110‑2

For engineers and test labs focused on hydraulic motor performance, ISO 4392-1 is a core reference for reliable, repeatable low‑speed hydraulic motor testing.