screw compressor has excessive vibration

Comprehensive Guide to Compressor Vibration Fault Diagnosis & Maintenance

1. Vibration Standards & Measurement

• Normal: ≤ 4.5 mm/s
• Attention Required: 4.5 ~ 7.1 mm/s
• Danger (Immediate Action Required): ≥ 7.1 mm/s

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2. Step-by-Step Troubleshooting Procedures

• Anchor Bolts: Perform a full-torque re-tightening (refer to the manufacturer's manual) and inspect for foundation cracks or loose shims.
• Levelness: Re-measure using a precision level. If deviation exceeds 0.1 mm/m, re-leveling is required.
• Piping Stress: Check if inlet/outlet hard pipes are exerting force on the machine. Inspect flexible connections for aging or cracking. Install support brackets (spacing ≤ 1.5m) to eliminate resonance.

• Precision Check: Use a dial indicator or laser alignment tool.
  • Radial deviation: ≤ 0.1 mm
  • Angular deviation: ≤ 0.5°
  • Axial deviation: ≤ 0.2 mm
• Component Check: Inspect the elastic element for damage and bolts for looseness.
• Thermal Compensation: During cold alignment, leave a clearance of 0.1 to 0.15 mm to account for thermal expansion.

• Oil Quality: Maintain the oil level at the center line of the sight glass. Change oil immediately if it turns black, emulsifies, or contains impurities (use OEM-recommended oil).
• Oil Circuit: Check for clogged oil filters and verify normal oil supply pressure. Insufficient lubrication leads to rapid bearing wear.

• Bearing Check:
  • Listen: Use a stethoscope for "rustling/gurgling" sounds.
  • Temperature: Monitor bearing housing temperature; a differential greater than 15℃ indicates abnormality.
• Rotor Check:
  • High-frequency vibration (> 100 Hz) is often caused by bearing or rotor issues.
  • Oil Sludge/Scaling: Requires disassembly, inspection, cleaning, and re-balancing.
  • Meshing Clearance: Normal clearance is 0.03–0.05 mm. Excessive wear or clearance requires repair or replacement.
  • Axial Movement: Excessive movement due to failed bearing preload can cause the rotor to touch the end cover, resulting in vibration and noise.

• Mechanical: Check for an unbalanced motor rotor, loose fan, or damaged bearings.
• Electrical: Imbalanced current, phase loss, or VFD harmonics can induce electromagnetic vibration.

• Air Path: Check for clogged intake filters, intake pulsation, or exhaust pressure fluctuations.
• Load Dynamics: Frequent loading/unloading cycles or abnormal slide valve operation can cause sudden load changes and vibration.

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3. Vibration Spectrum Analysis

• 1× Frequency: Indicates loose foundations, misalignment, or rotor imbalance.
• 2× / 3× Frequency: Indicates coupling misalignment or early-stage bearing failure.
• Meshing Frequency: Indicates rotor wear or abnormal clearance.
• High Frequency (> 500 Hz): Indicates bearing fatigue or rolling element failure.

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4. OEM-Specific Critical Points (Atlas Copco Standards)

• Bearing Clearance: Maintain a strict tolerance of 0.03–0.05 mm. Installation outside this tolerance is prohibited.
• Rotor Dynamic Balance: Grade G1 (≤5g·mm). Re-balance is mandatory after cleaning or if dirt accumulates.
• Internal Cleanliness: No foreign objects are allowed inside the main unit. After disassembly, thorough cleaning and torque-controlled reassembly are required.

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5. Recommended Inspection Sequence

1. Foundation & Installation
2. Coupling Alignment
3. Lubrication & Oil System
4. Operating Conditions & Airflow
5. Motor & Electrical System
6. Main Unit Internals