Practical Maintenance Guide for Industrial Fans and Blowers: Balancing, Belt Tension, Bearing Lubrication and Vibration Limits

1. Scope and Purpose

This maintenance guide covers essential procedures for the inspection, adjustment and verification of industrial fans and blowers used in various applications, including HVAC systems, fume extraction, pneumatic conveying and drying processes. The main objective is to ensure the reliable and efficient operation of this equipment, prevent premature failures and prolong its useful life. This intervention should be performed as part of scheduled preventive maintenance or when operational anomalies such as excessive noise, unusual vibration or increased bearing temperature are detected.

2. Safety Precautions

CRITICAL SAFETY WARNING!

• Lockout and Tagout (LOTO): Before any intervention, ensure that the fan or blower is completely de-energized and locked following the LOTO procedure (UNE-EN 1037). Verify the absence of voltage using a calibrated multimeter.
• Hazardous Energies: Identify and control all stored energies (electrical, mechanical, thermal, pneumatic) before starting work.
• Personal Protective Equipment (PPE): Always wear appropriate PPE, including safety glasses (EN 166), protective gloves (EN 388), safety footwear (EN ISO 20345) and hearing protection (EN 352). In dusty environments, use FFP2 or FFP3 mask (EN 149).
• Hot Surfaces: Avoid contact with motors, housings or ducts that may be at high temperatures.
• Moving Components: Never attempt to adjust, clean or lubricate components while the equipment is in operation. Make sure all moving parts have come to a complete stop.

3. Tools and Materials Required

4. Pre-Maintenance Checklist

5. Step by Step Procedure

1. Preparation and Isolation

   1. Lockout Tagout (LOTO): Activate the LOTO procedure. Disconnect power to fan/blower motor at main disconnect point. Apply locking devices and warning labels. Check the absence of voltage using a multimeter on the motor.
      Common error: Skipping the no-voltage check, which can result in serious electric shock.
   2. Work Permit: Ensure all necessary work permits are signed and posted.
   3. Initial Cleaning: Remove any visible buildup of dust, dirt, or debris from the fan's outer casing, blades, and motor. Use compressed air (with caution and appropriate PPE) or industrial vacuum.

2. Detailed Visual and Hearing Inspection

   1. Housing and Bracket: Inspect the fan housing and its supports for cracks, deformations, corrosion, or loose attachment points. Make sure all anchor bolts are tight and have no signs of movement.
      Common mistake: Ignoring small cracks that can propagate and cause structural failure.
   2. Blades/Rotor: Check the blades or rotor for material buildup, erosion, corrosion, cracks, or warping. The blades must be clean and undamaged. Knocks or nicks can affect the balance.
      Visual: The blades must have a uniform and clean surface, without apparent vibrations when rotating manually.
   3. Bearings and Housing: Visually inspect bearing housings for lubricant leaks, discoloration from overheating, or physical damage.
   4. Drive (Belts and Pulleys):
      • Belts: Inspect each belt for cracks, excessive wear, fraying, hardening, or signs of slippage (shining). Check that all straps are the same type and length.
      • Pulleys: Check pulleys for groove wear, corrosion, cracks, or misalignment. The slots must be smooth and free of burrs.
      
      Visual: Pulley grooves should match the shape of the belts, with no signs of excessive polishing or material buildup.
   5. Engine: Check the engine for cleanliness, dust accumulation on the cooling fins, condition of the engine fan and electrical fasteners.
   6. Auditory Inspection (manual): Manually rotate the fan/blower shaft (if possible and safe). Listen carefully using a mechanical stethoscope or directly at the bearing housings. Look for rubbing, grinding, creaking or knocking noises that may indicate damaged bearings or lack of lubrication.
      Criteria: The turn must be smooth and silent. Any abnormal noise is an indication of a problem.

3. Checking and Adjusting Belt Tension

   1. Tension Measurement: Use a belt tension meter (ultrasonic or mechanical) to verify the current tension of the belts. Consult the fan manufacturer's or belt manufacturer's specifications for recommended tension values ​​(UNE 53569).
      Typical values: For new V-belts, tension can be between 5-7 N/mm per belt. For used belts, 3-5 N/mm. These values vary significantly by strap type and size.
   2. Tension Adjustment: If the tension is not correct, loosen the motor fixing bolts and move the motor to increase or decrease the wheelbase. Make small, consistent adjustments to maintain parallelism. Tighten the motor fixing bolts to the specified torque (e.g. M12: 70-80 Nm; M16: 120-140 Nm). Measure the voltage again.
      Common error: Overtightening the belts, which causes overloading of the bearings and reduces the life of the belts.
   3. Pulley Alignment: Use a laser aligner to check pulley alignment. Make sure the faces of the pulleys are perfectly parallel and in the same plane. Make any necessary adjustments by loosening and repositioning the motor or pulleys. A misalignment of 0.5 mm per 100 mm of wheelbase is acceptable, but 0 mm is ideal.
      Visual: The laser beam must be projected continuously onto the targets of the opposite pulley, without deviations.

4. Bearing Lubrication

   1. Lubricant Identification: Check the type of lubricant (grease or oil) and the amount recommended by the bearing or fan manufacturer. Use only the specified lubricant to avoid incompatibilities.
   2. Cleaning Grease Nipples/Caps: Thoroughly clean grease nipples or oil housing caps to prevent contaminants from entering during lubrication.
      Common error: Not cleaning the grease nipples, introducing dirt directly into the bearing.
   3. Grease Application: Using a grease gun, slowly inject the recommended amount of grease. Generally, this is measured in grams or gun pulses. For bearings rotating at high speed, lubricate with the equipment running (if safe and recommended by OEM) for even distribution. For closed bearings, the amount can be 30-50% of the free volume.
      Typical value: 6205 bearing: 3-5g; Bearing 6310: 10-15g. Frequency can vary from weekly to annually, depending on speed, load and environment.
      Common error: Over-greasing, which generates excessive heat, seal pressure and premature failure. Excess fat acts as a brake.
   4. Oil Change: If the system uses oil lubrication, drain the old oil completely, clean the crankcase and refill with the specified volume and type of fresh oil. Check the oil level with the sight glass or dipstick.

5. Swing Verification and Vibration Limits

   1. Preliminary Vibration Measurement: Before any balance adjustment, perform a vibration measurement on the fan/blower (with the equipment running after power is restored). Measure the vibration speed (mm/s RMS) at the support points of the bearings in horizontal, vertical and axial directions, according to the standard ISO 10816-3.
      Vibration limits (ISO 10816-3, Class II - medium machines):

      Vibration Range	Machine Status
      Less than 1.1 mm/s RMS	Good (Zone A)
      1.1 mm/s to 2.8 mm/s RMS	Satisfactory (Zone B)
      2.8 mm/s to 7.1 mm/s RMS	Unsatisfactory (Zone C) - Requires corrective action
      Greater than 7.1 mm/s RMS	Unacceptable (Zone D) - Imminent damage, stop operation

   2. Rotor Balancing (if applicable): If vibrations exceed acceptable limits, especially at the rotor rotation frequency, balancing is required. This is a specialized procedure that typically requires portable dynamic balancing equipment. Follow the instructions of the equipment and the certified technician. The goal is to reduce the vibrations to the 'Good' or 'Satisfactory' zone.
      Consideration: Dirt buildup on the blades is a common cause of unbalance. Cleaning may resolve the problem before balancing with counterweights is required.

6. Reassembly and Final Testing

   1. Reinstallation of Guards: Reinstall all safety guards and protective covers for belts and moving parts. Make sure they are securely fastened.
      WARNING! Operating the equipment without guards is extremely dangerous.
   2. LOTO Removal: Unlock and remove LOTO tags only after confirming that all personnel are out of the danger area and that all tools have been removed.
   3. Start and Monitoring: Start the fan/blower. Closely monitor the initial operation. Listen for unusual noises. Check the temperature of the bearings with the infrared thermometer (normal operating temperature: 40-70°C; maximum: 95°C).
   4. Post-Maintenance Vibration Measurement: Perform a final vibration measurement to confirm that levels are within acceptable limits.

6. Post-Maintenance Verification Checklist

7. Troubleshooting Guide

8. Recommended Maintenance Schedule

9. Spare Parts Reference

To purchase these and other high-quality spare parts, visit our electronic catalog: www.unitecd.com/e-catalog/

10. References

• UNE-EN 1037: Machine safety. Prevention of untimely start-up.
• UNE-EN ISO 10816-3: Evaluation of machine vibration through measurements on non-rotating parts.
• UNE 53569: V and poly-V transmission belts. Calculation and application.
• UNE-EN ISO 6789: Manual dynamometric tools. Requirements and test methods for verification of design conformity, quality conformity and recalibration procedure.
• UNE-EN 166: Individual eye protection. Specs.
• UNE-EN 388: Protective gloves against mechanical risks.
• UNE-EN ISO 20345: Personal protective equipment. Safety footwear.
• UNE-EN 352: Hearing protectors.
• UNE-EN 149: Filtering half masks for protection against particles. Requirements, tests, marking.
• ISO 281: Bearings. Basic dynamic load and nominal life.
• Technical documentation from the original manufacturer (OEM) of the fan/blower and critical components (motor, bearings, belts).