Practical Manual for Maintenance of Cooling Towers: Filler, Water Treatment, Fan Balancing and Basin Cleaning

1. Scope & Purpose

This manual describes the essential maintenance procedures for industrial cross-flow cooling towers, critical to maintaining optimal thermal performance and long equipment life. Specific attention is paid to the inspection and cleaning of the filler, effective water treatment, balancing of the fan and thorough cleaning of the water basin. The procedures apply to periodic, preventive and corrective maintenance, and serve as guidance for qualified maintenance technicians to ensure the efficiency and safety of the cooling tower installation, in accordance with NEN standards for safe operations.

2. Safety measures

WARNING: Always perform a complete Lockout/Tagout (LOTO) procedure before beginning any work on the cooling tower. This includes completely de-energizing and locking out the electrical supply for the fan, circulation pumps and any dosing pumps. The water supply and drain must also be closed and secured against unintentional opening.
WARNING: Always wear the prescribed personal protective equipment (PPE) to protect yourself against mechanical, chemical and biological hazards. This includes, but is not limited to, safety helmet, safety goggles, chemical-resistant gloves (when handling water treatment agents), safety shoes, hearing protection (for fan work) and, if necessary, respiratory protection (when spraying biocides or cleaning in confined spaces).
WARNING: Be aware of moving parts such as fan blades, even when stationary, and hot water. There is a risk of slipping when working in the water basin. Take measures against Legionella contamination, as described in VDI 2047 Blatt 2 and local guidelines, by disinfection and avoiding aerosol formation.
WARNING: Enter confined spaces, such as the reservoir, only after a risk assessment and with proper confined space procedures, including air quality monitoring and presence of a standby person. Ensure sufficient ventilation.

3. Required Tools & Materials

The following tools and materials are essential for the safe and effective performance of maintenance procedures:

4. Pre-Maintenance Inspection Checklist

Perform this inspection before beginning detailed maintenance procedures to gain an initial idea of the cooling tower condition and identify potential problem areas.

5. Step-by-Step Procedure

This procedure describes the detailed steps for performing preventative maintenance on an industrial cooling tower.

5.1. Preparation & Safety Precautions

1. Insulating the Cooling Tower:
   • Perform the LOTO procedure:
   • Switch off the main switch for the fan and all pumps (circulation, dosing) and lock it. Confirm the absence of voltage with a suitable multimeter (in accordance with NEN 3140).
   • Shut off the main supply of make-up water and lock the valve.
   • Close the drain line unless it is used for emptying.
   • Avoid mistakes: Don't forget to isolate secondary power sources such as heating elements or control panels.
2. Putting on PPE: Wear at least a safety helmet, safety glasses, safety gloves (nitrile/PVC for chemicals) and safety shoes. If cleaning agents are used, or when working in the vicinity of the fan, add respiratory protection and hearing protection.
3. Setting off the work area: Place warning signs and cordon off the work area with barrier tape to keep unauthorized persons out.

5.2. Water Drainage & Cleaning Water Basin

1. Draining the basin:
   • Open the basin's drain valve and allow all water to drain to a suitable drain or holding tank, in accordance with local environmental regulations.
   • Avoid mistakes: Make sure the drained water is treated properly, especially if it contains biocides or other chemicals.
2. Removing coarse dirt:
   • Use brushes and scrapers to remove loose silt, leaves, mud and other coarse contaminants from the basin.
   • Use an industrial wet vacuum cleaner to suck up any remaining water and sludge.
3. High-pressure cleaning:
   • Clean the entire water basin, including walls and bottom, thoroughly with a high-pressure cleaner (150-200 bar). Remove all algae, biofilm and stubborn deposits. If necessary, use a suitable, cooling tower-safe cleaning agent (descaler or biocide).
   • Rinse the basin with clean water until all chemicals and dirt residues have been removed.
   • Avoid mistakes: Do not use abrasive tools that could damage the protective coating of the cymbal. Avoid spraying directly on sensors or vulnerable wiring.
4. Inspection of basin construction: After cleaning, check the internal coating and the construction of the basin for cracks, corrosion or other damage. Repair minor damage immediately with a suitable coating or sealant.

5.3. Inspection & Cleaning Filler (Fill Media)

1. Creating Access: Open the access hatches on the sides of the cooling tower to access the filler.
2. Visual inspection of filler:
   • Check the filler (usually PVC film fill) for excessive limescale, biofilm (slime layer), algae growth and blockages. Also pay attention to physical damage such as collapses, cracks or holes.
   • Visual indicator: Clean filler is free of visible deposits and has an open structure. Subsidence or blockage is immediately visible as tightly packed or misshapen sections.
3. Cleaning filler:
   • Use a high-pressure cleaner with a lower pressure (max. 50-80 bar) and a wide spray nozzle to gently clean the filler. Work from top to bottom to rinse off dirt and deposits.
   • In case of serious contamination, chemical cleaning may be necessary. Circulate a suitable cleaning agent (descaler, biocide) through the system, in accordance with the manufacturer's instructions, followed by a thorough rinse.
   • Avoid mistakes: Too high pressure can damage the filler. Always use chemicals that are compatible with the filler material.
4. Filler Replacement: Replace severely damaged or irreparably clogged sections of the filler. Make sure the new filler is installed correctly, with no cracks or open spaces that could cause bypass flow.

5.4. Inspection & Maintenance Fan System

1. Visual inspection of fan blades:
   • Inspect each fan blade for cracks, dents, edge erosion, or loose fasteners. Check the tightening torques of the blade mountings (typically 70-90 Nm for M12 bolts).
   • Visual indicator: Blades must be smooth, undamaged and securely mounted.
2. Lubricate and check bearings:
   • Check fan and motor bearings for play, noise and excessive heat (manually at standstill, or with temperature gauge after brief start-up if safe). Lubricate the bearings according to the OEM (Original Equipment Manufacturer) specifications, usually with an EP2-based lithium grease.
   • Avoid mistakes: Excessive lubrication can lead to bearing damage. Use the correct lubricant and the correct amount.
3. Check belt drive (if applicable):
   • Check the V-belts for wear, dry cracks, glazing or missing parts. If in doubt, replace the complete set of belts.
   • Measure the belt tension with a belt tension tester or check the deflection (typically 15-20 mm deflection per meter span at 5 kg pressure). Adjust the tension according to the manufacturer's specifications.
   • Align the pulleys with a laser alignment tool. A deviation of more than 0.5 mm per 100 mm distance is unacceptable and leads to premature belt wear and bearing damage.
   • Visual indicator: Belts should appear uniform with no tears or shiny spots. Pulleys must be perfectly aligned.
4. Fan balancing:
   • Use a vibration meter to measure the vibration of the fan system. The total vibration speed (RMS) must not exceed 4.5 mm/s (according to EN ISO 10816-3 for class 2 machines).
   • If the vibrations are too high, perform static or dynamic balancing on the fan blades. This may mean adding or removing small weights from the blades.
   • Avoid mistakes: Do not attempt to balance without appropriate equipment and training. Improper balancing can cause serious damage.

5.5. Inspection & Maintenance Water Distribution System

1. Check and clean nozzles:
   • Inspect all nozzles for blockages, wear, or damage. Clean clogged nozzles with a brush and flush them with water.
   • Visual indicator: Each nozzle must provide a complete and uniform spray pattern, without 'void' spots or jets.
2. Distribution pans/Distribution pipes: Check these for corrosion, leaks and deposits. Clean them thoroughly and repair any damage or leaks.

5.6. Inspection & Calibration Water Treatment System

1. Check metering pumps: Inspect the metering pumps, hoses and injection points for leaks, blockages or wear. Check whether the pumps function correctly and the chemicals (anti-corrosion, anti-fouling, biocides) are dosed correctly.
2. Chemical levels: Check the levels in the chemical tanks and replenish them if necessary.
3. Sensor calibration: Calibrate the pH and conductivity sensors according to the manufacturer's instructions. This is essential for correct water treatment.
4. Water quality tests: Take water samples and perform tests for pH value (typically 7.5-8.5), conductivity (maximum 2000-3000 µS/cm, depending on water make-up), hardness, alkalinity and biocide concentration. For Legionella prevention, follow the procedures specified in NEN 6265.

5.7. General Construction & Accessories

1. Frame and panels: Inspect the entire cooling tower structure (frame, side panels, doors) for signs of corrosion, dents, or loose fasteners. Repair or replace damaged parts.
2. Drip catchers and slats: Check these for damage, blockages and correct positioning. Clean them if necessary.
3. Float valve and overflow: Check the mechanical operation of the float valve and the overflow for any blockages.

5.8. Closing & Start-up

1. Reinstall: Properly replace and secure all access panels, grilles, and guards.
2. Cleanup: Remove all tools, materials, and debris from the work area.
3. Fill with water: Open the make-up water valve and fill the water basin to the operational level.
4. To cancel LOTO: Reverse the LOTO procedure to return the cooling tower to service.
5. Start-up and checking:
   • Start the circulation pumps and the fan.
   • Immediately check for leaks throughout the system.
   • Measures operating parameters: water temperature in/out (delta T typical 5-10 °C), motor amperage (within specifications), water pressure (according to P&ID).
   • Visual indicator: Even water distribution across the filler, normal noise levels and absence of visible leaks.

6. Post-Maintenance Verification Checklist

This checklist serves to confirm the correct operation of the cooling tower after maintenance.

7. Troubleshooting Guide

This table helps diagnose and resolve common cooling tower problems.

8. Recommended Maintenance Schedule

A strict maintenance schedule is necessary for the reliable operation and long life of the cooling tower.

9. Reference Parts

For an efficient maintenance strategy, it is important to have the most critical spare parts in stock. UNITEC-D GmbH supplies a wide range of quality parts for cooling towers, in accordance with EN and ISO standards.

For specific product information and orders, please consult our extensive e-catalog: www.unitecd.com/e-catalog/

10. References

• NEN-EN 13121-3: Filled cooling towers – Part 3: Design, construction and inspection of cooling towers in glass fiber reinforced plastic.
• VDI 2047 Blatt 2: Hygiene in cooling tower installations – Cooling towers with wet heat transfer.
• EN ISO 1940-1: Vibration measurement and evaluation of machines – Part 1: General guidelines.
• NEN 3140: Operation of electrical installations – Low voltage.
• OEM (Original Equipment Manufacturer) documentation for the specific cooling tower installation.
• Local laws and regulations regarding water quality and Legionella prevention (e.g. Water Worksheet 1.4G).