Last reviewed 30 July 2026
Compressor Balancing: Ensuring the Reliability of Compressed-Air Supply
In shortCompressor rotors are balanced to G2.5–G6.3 for screw types at 3,000–10,000 rpm, G2.5 for centrifugal at 10,000–30,000 rpm and G1–G2.5 for turbochargers at 50,000–150,000 rpm. Correction is by removing metal only — welding weights onto compressor rotors is prohibited.
When this applies
- After compressor overhaul or rotor cleaning
- Gradual vibration rise from deposits or erosion
- High-speed rotors needing tight grades G1-G6.3
- Turbocompressors requiring hot balancing
When it doesn’t
- Grade G2.5 is achievable with sound mechanics — the machine's condition sets the limit
- Welding weights onto rotors is prohibited
- Requires sound mechanics and rotors free of deposits
Compressors are the "heart" of many production facilities. Compressed air is used everywhere, from pneumatic tools to process control. A stopped compressor means a stopped production line.
Types of compressor and the specifics of balancing
1. Screw compressors
Design: two screw rotors (drive and driven) rotate within the casing
Speed: 3,000–10,000 rpm
Balance quality grade: G2.5–G6.3
The specifics:
- The rotors work as a pair — precise synchronisation is essential
- High rotational frequency → strict balancing requirements
- Oil cooling — deposits may build up
Balancing: performed in the rotor's own bearings; after an overhaul, precise adherence to grade G2.5 is required, with correction by removing metal.
2. Centrifugal compressors
Design: a rotor with impellers (working wheels)
Speed: 10,000–30,000 rpm
Balance quality grade: G2.5 (strict!)
Applications:
- Gas pipeline transfer stations
- Petrochemicals
- Metallurgy (blast-furnace blowers)
Criticality: unbalance at such speeds can lead to catastrophic destruction of the rotor!
3. Turbocompressors (turbochargers)
Speed: 50,000–150,000 rpm (extremely high!)
Balance quality grade: G1–G2.5 in practice. ISO 1940-1 lists turbo-chargers under G6.3; makers hold these rotors far tighter because of the speed.
The specifics: they run at high temperatures (up to 800°C on the turbine side). Balancing must account for thermal deformation.
4. Reciprocating compressors
The specifics: the main vibration comes from the reciprocating motion of the pistons, but the crankshaft and flywheel also require balancing.
Balancing: the flywheel and pulley are balanced in their own bearings, right on the machine. The inertia forces of the piston group act at 1× and 2× running speed and cannot be removed by balancing — if a trial weight fails to change the amplitude by 20–30%, the vibration is not unbalance.
Causes of compressor unbalance
1. Deposits on the rotor
Cause: oil deposits, combustion products (in turbocompressors), corrosion
Solution: regular cleaning, balancing after cleaning
2. Impeller erosion
Cause: abrasive particles in the air/gas, cavitation (in vacuum compressors)
Symptom: a gradual rise in vibration
3. High-temperature deformation
For turbocompressors: a rotor at 800°C deforms differently than at room temperature
Solution: balancing that accounts for the operating temperature (hot balancing)
The consequences of unbalance
Energy losses: an increase in vibration of 1 mm/s on a 100 kW compressor can lead to annual electricity losses of more than 2,000 kWh — an extra cost of around €600/year.
Technical consequences:
- Destruction of bearings (life cut by a factor of 5–10)
- Damage to the shaft seal (oil leakage)
- The rotor rubbing against the stator (a disaster!)
- Cracks in the casing
Economic consequences:
- Production stoppage: €4,000–20,000/day
- Repair: €8,000–80,000
- A new compressor: €60,000–600,000
The balancing process
Stage 1: Diagnostics
- Measuring vibration in the operating regime
- Spectral analysis (checking: unbalance or another cause?)
- Inspecting the bearings and seals
Stage 2: Disassembly and preparation
- Stop the compressor and let it cool
- Remove the rotor (a 1–3 day operation)
- Clean off deposits
- Fault inspection (checking geometry and integrity)
Stage 3: Balancing on a machine
Why centrifugal and turbo rotors (10,000+ rpm) go on a machine:
- High speeds demand precision accuracy
- Safe test runs at such speeds need a protective enclosure
- Grade G2.5 is achievable with sound mechanics — the machine's condition sets the limit
The process:
- Mount the rotor on the machine
- Low-speed balancing (500–1000 rpm)
- High-speed balancing (up to operating speed)
- Check the residual unbalance
- For turbocompressors: balancing at elevated temperature
Correction methods:
- Drilling into the impeller discs — removing metal
- Grinding the blades — for precise correction
- Balancing screws — in special threaded holes
The economics of compressor balancing
| Compressor type | Power | Balancing cost | Cost of downtime (1 day) |
|---|---|---|---|
| Small screw | 15–30 kW | €3,200–4,800 | €2,000–4,000 |
| Medium screw | 50–200 kW | €6,000–12,000 | €6,000–12,000 |
| Centrifugal | 500–5000 kW | €20,000–80,000 | €20,000–80,000 |
| Turbocompressor | — | €12,000–60,000 | €12,000–40,000 |
The ROI of preventive balancing
Example: a 100 kW screw compressor
Prevention:
- Balancing once every 3 years: €8,000
- Planned stoppage: 2 days = €16,000 in losses
- Total: €24,000
Without balancing (a breakdown):
- Destruction of bearings: €6,000
- Rotor repair: €14,000
- Unplanned downtime: 5 days = €40,000
- Total: €60,000
Saving: €60,000 − €24,000 = €36,000
ROI: prevention is 2.5× more cost-effective than an emergency repair
Conclusion
Compressors are critically important equipment. Balancing the rotors ensures reliable operation and prevents costly downtime. For compressors, balancing is not an option but a mandatory condition of safe operation.
Compressor balancing
Instruments and services for balancing compressor equipment
Quick checklist
- Measure vibration in the operating regime
- Run spectral analysis to confirm unbalance
- Inspect bearings and seals
- Stop, cool and remove the rotor
- Clean off deposits and check geometry
- Correct only by removing metal, never welding