1. Scope and objective
This guide details preventive and corrective maintenance procedures for open circuit cooling towers (TAR). This maintenance is essential to guarantee thermal efficiency, prevent corrosion, limit limescale encrustation, and above all, control the risk linked to bacterial proliferation (notably Legionella). These procedures apply to maintenance technicians working on industrial installations.
2. Safety Precautions
WARNING: RISK OF DANGEROUS AND BIOLOGICAL ENERGY.
The padlocking procedure (LOTO) is mandatory before any intervention on ventilation motors, pumps or dosing systems. Wearing the following personal protective equipment (PPE) is imperative: protective suit, chemical-resistant gloves (EN 374 standard), facial protection (EN 166 standard), and FFP3 mask (EN 149 standard) in case of risk of bacterial aerosolization when cleaning filling materials.
3. Required tools and materials
| Tool | Specification | Quantity |
|---|
| Torque wrench | Range 50 - 250 Nm | 1 |
| Digital multimeter | Accuracy < 1% (True RMS) | 1 |
| Vibrometer | Range 10 - 1000 Hz, ISO 10816 | 1 |
| Propeller anemometer | Range 0.5 - 30 m/s | 1 |
| Water quality tester | pH, Conductivity, RedOx | 1 |
| High pressure cleaner | Max 80 bars (for filling) | 1 |
4. Pre-maintenance checklist
| Element | Verification | Criteria | Notes |
|---|
| Basin | Sediment level | < 5 mm deposit | Drain if > 5 mm |
| Filling | Obstruction/Clogging | <20% obstructed surface | Cleaning required if > 20% |
| Fan | Blade clearance/tightening | No games detected | Torque 120 Nm |
| Water quality | Conductivity | < 2000 µS/cm | Adjust purge if outside threshold |
5. Step by Step Procedure
- Preparation and recording (LOTO)
- Identify energy sources (electric, hydraulic).
- Affix the padlocks and locking labels according to the NF standard EN 1037.
- Check the absence of voltage on the ventilation motors using the multimeter.
Frequent error: forgetting to lock out the water return valve, leading to overflow when opening the access points. - Pool cleaning and inspection
- Drain the pond completely.
- Manually remove sludge and debris.
- Inspect the walls for signs of corrosion (cracks, pitting).
- Clean the pump suction strainers (nominal flow must be restored).
- Inspection and cleaning of the filling media
- Visually inspect the physical condition (no deformation, no breakage).
- Use a high pressure cleaner set to a maximum of 80 bars to remove limescale and biological deposits.
- Never use a directional high pressure jet (Karcher turbo nozzle type) less than 50 cm away, this will destroy the structure of the PVC.
- Balancing the fans and inspecting the transmission
- Check the tightness of the hub bolts: torque 120 Nm.
- Check the play at the bearings (no axial or radial play tolerated).
- Measure the vibration speed: it must be < 4.5 mm/s RMS (compliant with the ISO 10816 standard).
- Check the tension of the belts (deflection according to manufacturer's specifications, typically 10-15 mm for a span of 500 mm).
- Water treatment and recommissioning
- Check the operation of the dosing pumps (biocide, corrosion inhibitor).
- Recharge the pool and reboot the system.
- Measure the parameters: pH (7.5 - 8.5), Conductivity (< 2000 µS/cm).
6. Post-maintenance verification
| Testing | Expected result | Real | Pass/Fail |
|---|
| Fan vibration | <4.5mm/s RMS | | |
| Water flow | Nominal (+/- 5%) | | |
| Engine consumption | < I nominal (wafer) | | |
7. Troubleshooting Guide
| Symptom | Probable cause | Corrective action |
|---|
| Excessive vibration | Dirty/unbalanced blades | Clean the blades, check the balancing |
| Water outlet temperature too high | Clogging of the filling | Clean or replace the filling |
| Insufficient water flow | Clogged strainer | Clean the strainer |
8. Recommended maintenance schedule
| Task | Frequency | Estimated duration | Skill level |
|---|
| Basin/Strainer Inspection | Monthly | 1h | Technician |
| Water chemistry analysis | Weekly | 0.5h | Operator |
| Complete cleaning (incl. filling) | Annual | 8h | Specialized technician |
| Fan balancing | Annual | 2h | Specialized technician |
9. Spare parts reference
| Description | Specification | UNITEC category |
|---|
| Fill media (block) | PVC, height 300mm | TAR replacement |
| Fan bearing kit | SKF/NSK waterproof | Transmission |
| Suction strainer | 316L stainless steel | Hydraulics |
To order your certified spare parts, please consult our online catalog: https://www.unitecd.com/e-catalog/
10. References
- NF EN 1037: Machine safety - Prevention of unintended start-up.
- ISO 10816: Mechanical vibrations - Evaluation of machine vibrations.
- INRS technical guide: Assessment of risks linked to legionella in ART.
