Diagnosing and Correcting Excessive Vibration in Rotating Equipment: A Guide for Technicians

1. Problem Description & Scope

This guide covers diagnosing and troubleshooting excessive vibration in rotating equipment, a common cause of failure and production loss in industrial environments. It focuses on installations such as pumps, fans, motors, compressors, gearboxes and turbines that are essential for continuous business operations in the Benelux manufacturing industry. Excessive vibration can lead to accelerated component wear, structural damage, increased energy consumption, unsafe working conditions and ultimately catastrophic machine failure. The severity of vibrations is classified as:

• Critical: Immediate shutdown of equipment is required to prevent serious damage or injury. Typically associated with vibration levels above the alarm thresholds according to ISO 10816.
• Major: Requires rapid planning of corrective actions. Production can continue temporarily, but the risk of deterioration is high. Vibration levels near the alarm threshold.
• Minor: Requires monitoring and scheduling for maintenance during planned downtime. Vibration levels above acceptable, but below alarm threshold.

2. Safety measures

Before performing any diagnostic or maintenance work on rotating equipment with vibration problems, it is absolutely essential to follow strict safety procedures to prevent personal injury and further damage to equipment.
Safety comes first, always!

WARNING!
Lockout/Tagout (LOTO): Ensure that all energy sources (electrical, hydraulic, pneumatic) are fully isolated and locked in accordance with the NEN 3140 standard and company procedures. Confirm the absence of voltage with appropriate test equipment.
Personal Protective Equipment (PPE): Always wear the required PPE, including safety glasses, hearing protection, safety shoes, gloves and suitable work clothing. Check for loose clothing or jewelry that could be caught by rotating parts.
Stored Energy: Be aware of stored energy in springs, accumulators, capacitors, or pressurized liquid and gas systems. Vent and relieve systems where necessary before carrying out work.
Hot Surfaces: Rotating equipment may have hot surfaces. Use thermal gloves and be careful.
Hazardous Substances: Identify and manage any hazardous lubricants, coolants or process media in accordance with applicable safety regulations and ATEX guidelines if applicable in potentially explosive areas.

3. Required Diagnostic Tools

The following specialized tools are crucial for effective vibration diagnosis:

4. Initial Assessment Checklist

Before you begin detailed vibration measurements, go through the following checklist to gather crucial information and streamline diagnosis.

5. Systematic Diagnosis Flowchart

Follow this decision tree to isolate the primary cause of vibration using spectrum analysis. (Conforms to ISO 13373-1:2018 for machine condition monitoring and diagnosis).

1. Identify High Vibration Levels
   1. Perform a broadband vibration measurement on bearing shells and machine house.
      Measurement point: Horizontal, Vertical, Axial on each bearing. Reference: ISO 10816-3 (industrial machines), ISO 20816-1 (general).
      Acceptable: Class A/B (e.g. 0-4.5 mm/s RMS for medium machines). Alarm: Class C/D (e.g. > 7.1 mm/s RMS for medium machines).
   2. If Vibration > Acceptable: Go to step 2 (Spectrum Analysis).
   3. If Vibration < Acceptable: Monitor periodically. No acute malfunction.
2. Spectrum Analysis (FFT) – Initial
   1. Collect vibration spectrum data with the vibration analyzer. Settings: Fmax = 100 x RPM (up to 60,000 cpm) or 1000 Hz, Lines = 1600, Averages = 4, Window = Hanning.
   2. Observe Dominant Peaks: Which frequencies are most prominent?
   3. Compare to Rotation Speed ​​(1X RPM):
      1. Is the dominant peak 1X RPM?
         1. Yes: Probable imbalance or misalignment. Go to step 3 (1X RPM Analysis).
         2. No: Go to step 4 (Non-1X RPM Analysis).
3. 1X RPM Analysis
   1. Peak only at 1X RPM, relatively few harmonics (2X, 3X):
      1. Is 1X RPM peak high in the radial direction (H/V)?
         1. Yes: Very likely Unbalance. Go to 'Diagnostic Matrix - Imbalance'.
      2. Is 1X RPM peak high in axial direction (A) or radial with 2X/3X harmonics?
         1. Yes: Probably Alignment error. Go to 'Diagnostic Matrix - Alignment Error'.
      3. Is the 1X RPM peak high and in phase at all measurement points?
         1. Yes: Probably Fundamental Mode Resonance. Go to step 5 (Resonance Analysis).
4. Non-1X RPM Analysis
   1. Dominant peaks at higher frequencies (2X, 3X, 4X RPM, etc.)?
      1. Yes: Likely Alignment error (specifically coupling or angular alignment errors), Mechanical Looseness, or Bearing faults. Go to 'Diagnostic Matrix - Alignment Error' or 'Diagnostic Matrix - Mechanical Looseness' or 'Diagnostic Matrix - Bearing Errors'.
   2. Dominant peaks at sub-synchronous frequencies (<1X RPM, e.g. 0.4X-0.48X RPM)?
      1. Yes: Probably Oil scraping/Swirl (in plain bearings). Go to 'Diagnostic Matrix - Oil Scrape'.
   3. Dominant peaks at bearing frequencies (BPFI, BPFO, FTF, BSF)?
      1. Yes: Very likely Bearing fault. Go to 'Diagnostic Matrix - Bearing Faults'.
   4. Dominant peaks on gear frequencies (GMF, GMF harmonics, sidebands)?
      1. Yes: Probably Gear problems (wear, backlash, incorrect engagement). Go to 'Diagnostic Matrix - Gear Problems'.
   5. High vibration in a wide frequency range (noise floor increased)?
      1. Yes: Probably Cavitation (pumps), Friction, Electrical Problems (motors). Go to 'Diagnostic Matrix - Miscellaneous Problems'.
5. Resonance Analysis (If suspected)
   1. Perform a Run-Up/Coast-Down test with continuous vibration measurement. Observation: A rapid increase and decrease in vibration amplitude as the machine passes through a certain speed (critical speed) indicates resonance. Impact: Very high vibrations that increase linearly with speed, but suddenly peak around the critical speed. Confirmation: Compare critical speed with the vibration frequencies of the machine parts and structure.
   2. Go to 'Diagnostic Matrix - Resonance'.

6. Error Cause Matrix

This matrix describes common symptoms in the vibration spectrum, possible causes and the expected results upon confirmation. (Based on VDI 3832 guidelines).

Imbalance

Misalignment

Bearing faults (Rolling Element Bearings)

Mechanical Looseness

Resonance

7. Root Cause Analysis for Each Error

7.1 Imbalance

Why it happens: Imbalance occurs when the mass of a rotor is not uniformly distributed around the axis of rotation. This may be due to:

• Manufacturing defects: Tolerances in component production.
• Wear or corrosion: Uneven material removal on blades or vanes.
• Dirt accumulation: Accumulation of process material on rotating parts (e.g. fan blades).
• Repairs: Improperly performed repairs or replacement of parts without rebalancing.
• Missing parts: Loss of balancing weights or small components.

How to confirm: The primary indication is a dominant vibration peak at 1X RPM in the spectrum, mainly in the radial direction. The amplitude of this peak generally increases quadratically with the speed. Phase measurements show that the vibrations on either side of the bearing are almost in phase in the radial direction (0-30 degrees). A balancing test will confirm the imbalance and indicate the location of the necessary correction weight.

Damage if left unresolved: Imbalance leads to increased radial forces on bearings and seals, resulting in accelerated wear and reduced service life. It can also lead to loosening of fasteners, foundation damage and excessive stress on the axle, potentially resulting in axle breakage.

7.2 Misalignment

Why it happens: An alignment error occurs when the axes of rotation of two coupled machines are not perfectly co-linear. This may involve radial (offset) and/or angular alignment errors. Causes are:

• Improper installation: Poor alignment during installation.
• Thermal Growth: Machines expand at operating temperature, changing alignment. Compensation for this is essential.
• Foundation problems: Subsidence, loose foundation bolts or 'soft foot' (uneven support of the machine feet).
• Pipe stresses: Forces from connected pipework that pull the machine out of position.
• Wear: Wear of machine feet or shims.

How to confirm: Alignment errors often manifest as dominant peaks at 1X and 2X RPM, often with higher harmonics (3X, 4X RPM). Angular misalignments typically cause high axial vibrations, while parallel offset misalignments lead to high radial vibrations with a dominant 2X RPM peak. Laser alignment tools provide final confirmation by measuring the exact deviations. Phase measurements generally show a large phase shift (approximately 180 degrees) across the coupling.

Damage if unresolved: Alignment errors generate cyclic bending stresses in the shaft, excessive axial and radial forces on bearings and seals, and increased temperature in the coupling. This results in premature bearing failure, seal leaks, coupling damage, increased energy consumption and potential shaft breakage.

7.3 Bearing Errors (Rolling Element Bearings)

Why it happens: Bearings are critical components that support rotation. Errors can occur due to:

• Lubrication problems: Insufficient, excessive, wrong type or contaminated lubrication.
• Contamination: Ingress of dust, moisture or metal particles.
• Installation errors: Improper installation, excessive interference fit, damage during installation.
• Overload: Excessive radial or axial loads.
• Fatigue: Material fatigue after prolonged use.
• Corrosion: Exposure to moisture or aggressive chemicals.

How to confirm: Bearing errors manifest in the vibration spectrum as peaks at the calculated bearing frequencies (BPFI, BPFO, BSF, FTF), often with sidebands around 1X RPM. In the early phase these peaks are often small and visible with envelope analysis (high frequency acceleration). As damage progresses, the peaks become larger and broader, and an increase in bearing temperature can be observed with a thermal camera.

Damage if left unresolved: Bearing failures lead to increased friction, overheating and increased vibration, ultimately resulting in catastrophic bearing failure and secondary damage to the shaft and machine housing. Production downtime and high repair costs are the result.

7.4 Mechanical Looseness

Why it happens: Mechanical looseness indicates a lack of structural integrity in the machine or its mountings. This could be:

• Foundation looseness: Loose anchor bolts, cracked concrete foundation.
• Structural looseness: Cracks in the machine frame, loose welds, worn machine feet.
• Component looseness: Play in bearings or bushings, loose rotor parts on the shaft, worn keyways.

How to confirm: Mechanical looseness is often characterized by a complex vibration spectrum with high 1X RPM and harmonics (2X, 3X RPM), sometimes with sub-harmonics (0.5X RPM), and an elevated noise floor. The phase may be unstable. Visual inspection and manual testing (prying) may reveal loose components. A dial indicator can quantify excessive play in bearings or fits.

Damage if left unresolved: Looseness leads to instability, excessive stress on bearings and other components, and friction. This results in accelerated wear, fatigue cracking in structures, and the potential for components to loosen and cause catastrophic damage.

7.5 Resonance

Why it happens: Resonance occurs when an excitation frequency (for example, the rotational speed of the machine or a harmonic thereof) coincides with a natural frequency of the machine or its supporting structure. At resonance, energy is transferred efficiently, leading to extremely high vibration amplitudes even at relatively low excitation forces. Causes:

• Design errors: Natural frequency too close to operating speed.
• Structural changes: Adjustments to the foundation or machine that affect stiffness.
• Degradation: Cracks in foundation or frame that reduce stiffness, causing natural frequency to decrease.
• Imbalance/Misalignment: Although not the cause, these 'excitation forces' can activate resonance if the frequencies match.

How to confirm: A Run-up/Coast-down test is the most effective method. The machine is gradually switched on and off while continuous vibration data is collected. A rapid and significant increase in vibration amplitude at a specific speed (critical speed) confirms resonance. Modal analysis (with impulse test) can identify the natural frequencies of the structure. Vibrations due to resonance are often difficult to reduce with balancing or alignment unless the unbalance/alignment error is the primary excitation source.

Damage if left unresolved: Resonance can lead to extremely high dynamic stresses in components and structures, resulting in fatigue cracking, loosening of fasteners, and ultimately structural failure or even disintegration of the machine. This is often a critical failure that requires immediate action.

8. Step-by-Step Troubleshooting Procedures

8.1 Imbalance Correction

1. Safety First: Activate LOTO. Provide safe access to the rotor.
2. Cleaning & Inspection: Clean the rotor thoroughly. Inspect for dirt buildup, missing balance weights, or damage.
3. Balancing: Use a portable field balancing kit (according to ISO 21940-12).
   1. Place acceleration sensor and tachometer on the machine.
   2. Start the machine (if safe and controlled) and measure the initial vibration and phase at 1X RPM.
   3. Place a test weight at a predetermined position on the rotor.
   4. Measure vibration and phase again.
   5. Calculate the required correction weight and angular position with the balancing software.
   6. Insert the correction weight. Repeat measurements if necessary until vibrations are within tolerances (e.g. < 2.8 mm/s RMS for G2.5 according to ISO 21940-11).
4. Verification: After balancing, perform a full vibration analysis to confirm effectiveness.

8.2 Alignment Error Correction

1. Safety First: Activate LOTO. Disconnect the coupling.
2. Initial Check: Check for 'soft foot' with a dial indicator (max. 0.05 mm deviation on the foot). Correct with precision shims (UNITEC Category: Assembly aids).
3. Laser alignment: Use a laser alignment tool (e.g. Pruftechnik Rotalign).
   Procedure:
   1. Attach laser transmitters/receivers to the axes.
   2. Take a measurement; the system shows the radial and axial deviations.
   3. Calculate the required vertical and horizontal corrections (shims under the motor feet, displacement of the motor).
   4. Make corrections (move the engine with jacks and jackscrews, install or remove shims).
   5. Repeat the measurement until the values ​​are within tolerances (e.g. less than 0.03 mm offset and 0.03 mm/100 mm angular deviation).
4. Verification: Manually rotate the shaft 360 degrees to check the consistency of the alignment. After tightening the foundation bolts, rotate the axle again to check for soft foot induced by tightening. After alignment, perform a complete vibration analysis.

8.3 Bearing replacement

1. Safety First: Activate LOTO.
2. Preparation: Disassemble machine parts to access the bearing. Use a bearing heater to remove stuck bearings.
3. Shaft & Housing Inspection: Clean and inspect the axle and bearing housing for damage, contamination, or wear. Check dimensions (diameters, fits) with a micrometer.
4. Bearing choice: Select the correct UNITEC bearing (according to specifications, type: Ball, Roller bearing, etc., certification CE, TUV).
5. Mounting: Use appropriate mounting techniques:
   1. Cold Mounting: Small bearings with a hydraulic press or mounting kit to prevent force on the balls/rollers.
   2. Hot Assembly: Heat the bearing inductively to a maximum of 120°C (NEVER with an open flame) for larger bearings to create expansion. Use suitable gloves and tools.
   3. Hydraulic Mounting: For very large bearings, use hydraulic pressure.
6. Lubrication: Apply the correct amount and type of lubricant (per OEM specifications). UNITEC offers various industrial lubricants.
7. Seals: Always replace the seals together with the bearing (UNITEC Category: Seals).
8. Verification: Assemble machine parts. Perform a test run and check for noise, temperature (thermal camera) and vibration (vibration analyzer).

8.4 Remedy Mechanical Looseness

1. Safety First: Activate LOTO.
2. Identification: Locate the source of looseness (visual, hammer/pry test, phase measurements).
3. Tighten/Strengthen:
1. Loose Bolts: Torque all mounting bolts to the correct torque (refer to OEM specifications or ISO 4014 for standard bolts). Use a calibrated torque wrench.
2. Cracked frame/foundation: Repair cracks by welding (if metal and possible) or reinforce the foundation with chemicals/concrete injection. Consider strengthening with additional support beams.
3. Bearing clearance: Replace bearings if clearance exceeds tolerance (see Bearing Replacement).
4. Loose components: Check keyways, locknuts, crimp connections. Repair if necessary (e.g. new key, loctite, crimp).
4. Verification: After repair, perform vibration analysis to confirm harmonic reduction and noise floor.

8.5 Resonance Control

1. Safety First: Activate LOTO.
2. Frequency shift: The most effective method is to shift the natural frequency away from the excitation frequency.
   1. Increase stiffness: Add structural reinforcements (e.g. additional supports, thicker plates, cross beams).
   2. Reducing stiffness: (Less often, but sometimes possible) Remove unnecessarily stiff connections.
   3. Changing mass: Adding or removing mass to change the natural frequency (e.g. weights on the foundation or structure).
3. Add damping: Install damping materials or vibration dampers to absorb energy (UNITEC Category: Vibration dampers).
4. Excitation Change: If possible, change the operating speed of the machine to move the excitation frequency away from the natural frequency. However, this is often impractical.
5. Verification: Perform another Run-up/Coast-down test or Modal Analysis to confirm that the natural frequency has shifted sufficiently and the vibration amplitudes are within tolerances.

9. Preventive Measures

Prevention is better than cure. Implement these preventative strategies to minimize vibration problems.

10. Spare Parts & Components

For a quick and efficient solution to vibration problems, it is crucial to have the right spare parts in stock. UNITEC D GmbH offers a wide range of certified components that comply with NEN, EN and ISO standards.

Visit the UNITEC D GmbH e-catalogue for the complete range of spare parts.

11. References

• ISO 10816-series: Mechanical vibrations – Evaluation of machine vibrations by measuring on non-rotating parts.
• ISO 20816-series: Mechanical vibration – Measurement and evaluation of machine vibration.
• ISO 13373-1:2018: Machine condition monitoring and diagnosis – Vibration condition monitoring – Part 1: General guidelines.
• ISO 15243: Rolling Bearings – Damage and Failure – Terminology, Classification and Causes.
• ISO 21940-series: Mechanical vibration – Balancing of rotating machines.
• NEN 3140: Operation of electrical installations – Low voltage.
• EN 61010: Safety requirements for electrical measuring, regulating and laboratory equipment.
• EN 13187: Thermal performance of buildings – Qualitative detection of thermal irregularities in building envelopes – Infrared method.
• VDI 3832: Schwingungsanalyse an Wälzlagerungen von Maschinen (German).
• OEM documentation: Always consult the specific machine manufacturer's manuals for detailed tolerances and procedures.
• Related UNITEC D GmbH maintenance guides: See our website for guides on bearing installation, laser alignment and preventive maintenance.