1. Scope & Purpose
This guide defines standard procedures for the inspection, replacement and correct installation of hydraulic hoses used in CNC machine tools and industrial automation lines. The goal is to prevent catastrophic failures, reduce machine downtime and ensure operator safety. Maintenance must be carried out in compliance with the UNI EN ISO 4413.
2. Safety Precautions
WARNING: HIGH PRESSURE HYDRAULIC FLUID CAN CAUSE SERIOUS INJURY OR DEATH.
BEFORE ANY OPERATION:
- Perform the Lockout/Tagout (LOTO) of the machine and isolate the hydraulic power source.
- Completely depressurize the entire system. Don't rely solely on pressure gauges.
- Wear mandatory PPE: waterproof safety glasses, oil-resistant gloves and fireproof clothing.
- Never look for leaks with your bare hands; use cardboard or a piece of wood to detect any splashes.
3. Tools & Materials Required
| Tool | Specify | Quantity |
|---|---|---|
| Torque wrench | Range 10-250 Nm | 1 |
| Digital caliper | Accuracy 0.05 mm | 1 |
| Specific pipe cutter | For braided hoses | 1 |
| Hydraulic oil | ISO VG 32/46 (Compatible) | Q.B. |
| LOTO kit | Personal and unique | 1 |
4. Pre-Maintenance Inspection Checklist
| Item | Check | Acceptance/Rejection | Notes |
|---|---|---|---|
| External surface | No cracks or cuts | Accept if < 1mm | Replace if metal braid is exposed |
| Fittings | No corrosion or deformation | Reject if deformed | Check the integrity of the thread |
| Curvature radius | Minimum radius compliance | Accept if > minimum radius | Refer to the manufacturer's technical data sheet |
| Temperature | No stiffening/cracking | Accept if flexible | Sign of thermal aging |
5. Step-by-Step Procedures
1. Isolation and Depressurization
- Stop the machine and activate the LOTO protocol on the electrical and hydraulic power.
- Slowly open the circuit relief valve to eliminate residual pressure. Never force sudden openings if the system is under pressure.
2. Removal and Inspection
- Disconnect the fittings using two wrenches to avoid twisting the hose.
- Inspect the inside of the removed fitting for residual contamination or rubber degradation. Never reuse fittings with damaged or deformed threads.
3. Selection and Cut
- Verify that the new hose has the correct specifications (pressure rating, temperature, chemical compatibility).
- Cut the tubing to the required length adding 3-5% allowance for shrinkage under pressure.
4. Assembly and Installation
- Clean the new hose thoroughly with filtered compressed air.
- Tighten the fitting to the prescribed torque (consult the manufacturer's specific tightening torque table, e.g. for JIC fittings: 1/2'' = 40-50 Nm).
- Install the tube avoiding twisting. A twist of even a few degrees reduces the useful life of the hose by 50%.
5. Routing
- Secure the route using cable ties every 500-800 mm.
- Maintain a safe distance from moving parts.
6. Post-Maintenance Verification Checklist
| Tests | Expected Result | Actual | Pass/Fail |
|---|---|---|---|
| Pressure test | No leaks at operating pressure | -- | -- |
| Visual inspection | Dry fittings | -- | -- |
| Functional test | Smooth movement without constraints | -- | -- |
7. Troubleshooting Guides
| Symptom | Probable Cause | Corrective Action |
|---|---|---|
| Leak from the fitting | Insufficient tightening or damaged seal | Check torque, replace gasket |
| Burst pipe | Pressure above the limit or water hammer | Check relief valve, recalibrate |
| Obvious abrasions | Rubbing against metal parts | Reprofile the routing, add protective sheath |
8. Recommended Maintenance Schedule
| Tasks | Frequency | Estimated duration | Skill Level |
|---|---|---|---|
| Visual inspection | Weekly | 15 min | Basic technician |
| Leak test | Monthly | 30 min | Expert technician |
| Preventive replacement | Every 2-3 years | 2 hours | Specialized technician |
9. Spare Parts Reference
| Description | Specify | UNITEC category |
|---|---|---|
| High pressure hose | DIN EN 853 2SN | Hydraulics/Pipes |
| Straight fitting | Galvanized steel | Hydraulics/Fittings |
| Protective sheath | Anti-abrasion | Hydraulics/Accessories |
To purchase certified spare parts, consult our online catalogue: https://www.unitecd.com/e-catalog/
10. References
- UNI EN ISO 4413: Fluid power — General rules and safety requirements for systems and their components.
- DIN EN 853: Rubber-covered hydraulic hoses — Wire braid reinforced types — Specification.
- Guidelines for CNC machine tool manufacturers.
