Specification for fabric reinforcement of plastic hoses and hose assemblies for hydraulic use (draft)
1Key Takeaways
DIN EN ISO 3949 Plastics hoses and hose assemblies – Textile-reinforced types for hydraulic applications – Specification This specification applies to textile-reinforced plastic hoses and hose assemblies designed for hydraulic applications. It covers requirements for materials, dimensions, performance, and testing meth…
2Expert Interpretation
This in-depth analysis of the ISO 3949:2016 international standard for textile-reinforced thermoplastic hydraulic hoses covers the dimensional tolerances, pressure ratings, impulse testing, and electrical conductivity requirements for the three models R7/R8/R18, providing professional technical guidance for hose selection in hydraulic systems.
Standard Overview and Technical Background
ISO 3949:2016 is the International Organization for Standardization's technical specification for textile-reinforced thermoplastic hoses and hose assemblies, specifically for hydraulic applications. This fifth edition, which replaces the 2014 edition, primarily updates Chapter 1, Scope Definition, and includes technical revisions to Sections 7.1, 7.3, 10.1, and 10.2. The standard applies to three types of textile-reinforced hoses with nominal sizes 3.2 to 25, divided into two grades based on electrical conductivity requirements.
Product classification and structural requirements
The standard divides hoses into three main types, the difference is the maximum working pressure:
| Type | Maximum working pressure | Reinforcement layer structure | Applicable temperature range |
|---|---|---|---|
| R7 Type | 7.0-21.0 MPa | One or more layers of textile reinforcement | -40°C to +100°C |
| R8 Type | 14.0-42.0 MPa | One or more layers of textile reinforcement | -40°C to +100°C |
| R18 type | 21.0 MPa basis | One or more layers of textile reinforcement | -40°C to +100°C |
Each type is further divided into two grades based on electrical performance: Grade 1 (no electrical requirements) and Grade 2 (non-conductive). The hose must consist of a seamless thermoplastic inner layer resistant to hydraulic fluids, a suitable textile yarn reinforcement, and an outer layer resistant to hydraulic fluids, water, and weathering. The outer layer of Grade 2 hoses must not be perforated and must be orange (RAL 2004 color code).
Dimensional Tolerances and Geometrical Characteristics
The standard stipulates strict tolerance requirements for hose dimensions, which are implemented in accordance with the ISO 4671 measurement method:
| Nominal Size | Inner Diameter Range (mm) | R7 Maximum Outside Diameter (mm) | R8 Maximum Outside Diameter (mm) | R18 Maximum Outside Diameter (mm) |
|---|---|---|---|---|
| 3.2 | 3.4-4.0 | 9.5 | 10.5 | 9.5 |
| 5 | 4.6-5.4 | 11.4 | 14.6 | 10.8 |
| 6.3 | 6.2-7.0 | 13.7 | 16.8 | 13.5 |
| 8 | 7.7-8.5 | 15.6 | 18.6 | 16.6 |
| 10 | 9.3-10.3 | 18.4 | 20.3 | 18.4 |
| 12.5 | 12.3-13.5 | 22.5 | 24.6 | 22.8 |
| 16 | 15.5-16.7 | 25.8 | 29.8 | 27.2 |
| 19 | 18.6-19.8 | 28.6 | 33.0 | 31.5 |
| 25 | 25.0-26.4 | 34.7 | 38.6 | 40.4 |
Concentricity requirements vary according to nominal size: for hoses ≤6.3mm, the wall thickness variation shall not exceed 0.8mm; for hoses 6.3-19mm, the variation shall not exceed 1.0mm; for hoses >19mm, the variation shall not exceed 1.3mm.
Hydraulic performance requirements
The standard specifies strict hydraulic performance test requirements. All tests must be carried out in accordance with ISO 1402 hydrostatic test methods:
Pressure performance indicators
| Nominal size | R7 type working pressure (MPa) | R8 type working pressure (MPa) | R18 type working pressure (MPa) | Minimum bursting pressure ratio |
|---|---|---|---|---|
| 3.2 | 21.0 | 42.0 | 21.0 | 4:1 |
| 5 | 21.0 | 35.0 | 21.0 | 4:1 |
| 6.3 | 19.2 | 35.0 | 21.0 | 4:1 |
| 8 | 17.5 | 31.0 | 21.0 | 4:1 |
| 10 | 15.8 | 28.0 | 21.0 | 4:1 |
| 12.5 | 14.0 | 24.5 | 21.0 | 4:1 |
| 16 | 10.5 | 19.2 | 21.0 | 4:1 |
| 19 | 8.8 | 15.8 | 21.0 | 4:1 |
| 25 | 7.0 | 14.0 | 21.0 | 4:1 |
At maximum working pressure, the hose length shall not vary more than ±3%. When tested at the minimum bend radius, the hose shall be bent to the specified radius under no pressure and shall not flatten more than 10% of the original outside diameter.
Impulse Testing and Endurance Performance
Impulse testing is performed in accordance with ISO 6803, with the test fluid temperature at 100°C:
- R7 hose: At least 150,000 impulse cycles at an impulse pressure of 125% of the maximum working pressure.
- R8 and R18 hoses: At least 200,000 impulse cycles at an impulse pressure of 133% of the maximum working pressure.
No leakage or other failure shall occur before the specified number of cycles. This test is destructive and the specimen must be destroyed.
The low-temperature flexibility test is carried out in accordance with ISO 10619-2:2011 method B at -40°C. No cracks shall appear in the inner and outer layers. After returning to ambient temperature, the specimen shall not leak or rupture during the proof pressure test.
Fluid Compatibility and Chemical Resistance
The standard requires that the hose material must be compatible with various hydraulic fluids. The test is carried out using an inner and outer molded piece of at least 2mm thickness:
| Test Fluid | Test Conditions | Volume Change Rate Requirement | Applicable Standards |
|---|---|---|---|
| IRM 903 Oil | 100°C±3°C, 72 hours | -15% to +35% | ISO 1817 |
| Water-based fluid (ethylene glycol/water 1:1) | 70°C±1°C, 168 hours | 0% to +25% | ISO 1817 |
| Distilled water | 70°C±1°C, 168 hours | -10% to +25% | ISO 1817 |
Ozone Resistance test according to ISO 7326:2006 Method 1 or 2, depending on the nominal inside diameter of the hose. The outer layer shall not show any cracks or deterioration under 2x magnification.
Electrical Performance Requirements (Grade 2 Hose)
Grade 2 hose must meet the non-conductive requirements according to the test method in Appendix D:
- Test Conditions: 37.5kV AC, 50-60Hz
- Test Duration: 5 minutes ± 15 seconds
- Maximum Allowable Current: ≤50μA
- Preconditioning: 23°C ± 3°C, ≥85% relative humidity, 168 hours
During the test, the hose assembly must have a free length of 150mm ± 10mm, no fluid present, and both ends sealed to prevent moisture. Surface moisture must be wiped clean with a dry cloth.
Test Frequency and Quality Control
The standard specifies three types of tests:
Type Test
Confirms that hoses of a specific design and manufacturing process meet all standard requirements, repeated up to once every five years, or when the manufacturing method or material is changed.
Routine Test
Tests that must be performed on each finished hose before shipment, including dimensional measurement, static pressure testing, visual inspection, etc.
Production Test
Quality control test during the production process, recommended to be conducted once every 3,000 meters of each type and specification produced, or once every 12 months.
Marking and Labeling Requirements
The hose must be marked with the following information at least, and the marking must be repeated at least every 760mm:
- Manufacturer’s name or logo
- Nominal number of this standard ISO 3949
- Type and grade (e.g. R7-1)
- Grade 2 hose is marked with “NICHT LEITEND” (non-conductive)
- Nominal size
- Maximum working pressure (MPa and/or bar)
- Year and quarter of manufacture (e.g. 3Q16 means the third quarter of 2016)
Example: XXX/ISO 3949/R7-1/16/10,5 MPa (105 bar)/3Q16
Implementation recommendations and application guidelines
Selection recommendations
Select the appropriate hose type based on the hydraulic system's operating pressure: Type R7 is suitable for low- and medium-pressure systems (7-21 MPa), Type R8 is suitable for high-pressure systems (14-42 MPa), and Type R18 is designed for 21 MPa operating pressure. When considering fluid compatibility, be sure to consult the hose manufacturer to confirm the compatibility of the specific fluid with the hose material.
Installation and Use
During installation, ensure the minimum bend radius meets the requirements of Table 6 to avoid damage to the hose due to excessive bending. System design should account for hose length variations (maximum ±3%) and allow sufficient margin.
Maintenance and Replacement
Regularly inspect the hose for defects such as cracks, bulges, and wear. Store and use according to ISO 8331 guidelines, avoiding direct sunlight, high temperatures, and contact with chemicals. It is recommended to maintain a hose usage record, recording installation dates and operating conditions, to facilitate predictive maintenance.
Quality Control
When purchasing, suppliers should be asked to provide test certificates to verify that the hose complies with the ISO 3949 standard. For critical applications, it is recommended to conduct an incoming inspection, including dimensional measurements, pressure testing, etc.
By following the technical requirements and recommendations of this standard, the safe and reliable operation of textile reinforced hydraulic hoses in various hydraulic systems can be ensured, extending their service life and reducing the risk of failure.