Hydraulic fluid power — Valves — Determination of pressure differential/flow characteristics
1Key Takeaways
This document specifies methods for determining, under steady-state conditions, the pressure differential caused by the flow through any given path in a hydraulic fluid power valve. Requirements for test installations, procedures and presentation of results are specified.
2Expert Interpretation
Comprehensive interpretation of ISO 4411:2019 international standard for hydraulic valve differential pressure/flow characteristic testing, covering test device requirements, measurement accuracy classification, test process specifications and result presentation methods, and providing technical points and industry application cases for standard implementation.
Analysis of the core content of the standard
The ISO 4411:2019 standard specifies a unified test method for the differential pressure/flow characteristics of valves in hydraulic fluid power systems under steady-state conditions.
- Simplify the term "volume flow" to "flow"
- Change the flow symbol from "qv" to "q"
- Optimize the quality of illustrations (Figure 1, Figure 2)
Key technical requirements for test devices
| Components | Class A requirements | Class C requirements |
|---|---|---|
| Upstream straight pipe section | ≥10d | Negotiable |
| Pressure measurement accuracy | ±1.0% | ±5.0% |
| Temperature control | ±1.0K | ±4.0K |
Application case: Servo valve test
When a certain type of four-port servo valve is tested according to Class A accuracy, a standard pressure plate (Figure 2) is required, and its interface size should comply with ISO 10372 requirements. During the test, the oil cleanliness is maintained at NAS 6 level, the temperature is controlled at 40±1℃, and the pressure difference curve of the P→A passage is measured as shown in Figure 3.
Implementation of measurement accuracy classification
The standard divides measurement accuracy into three levels:
- Class A: Scientific research level accuracy, requiring on-site measurement of fluid density and viscosity
- Class B: Engineering acceptance level, allowing the use of fluid parameters provided by the supplier
- Class C: Production inspection level, with system error relaxed to 5%
Standard evolution and industry impact
Compared with the 2008 version, the 2019 version revision makes the standard more adaptable to the digital needs of contemporary hydraulic systems:
- Simplify the terminology system and keep in harmony with IEC standards
- Add a pre-test checklist in Appendix B to reduce implementation deviation
- Clearly define the system independence requirements for composite valves such as pilot-operated relief valves
Implementation suggestions
1. For cartridge valve testing, the standard pressure plate solution is preferred
2. The flow measurement point should be arranged at a distance of ≥5d behind the temperature measurement point
3. The test report must include fluid viscosity (cSt) and density (kg/m³) data