Compressor Balancing: Ensuring the Reliability of Compressed-Air Supply
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: only on a specialised machine after an overhaul. It requires precise adherence to grade G2.5.
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: imbalance 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
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 crankshaft and flywheel are balanced on special machines, accounting for the dynamics of the piston group.
Causes of compressor imbalance
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 imbalance
⚡ 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: imbalance 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 only on a machine:
- High speeds demand precision accuracy
- It is impossible to create safe conditions in the bearings
- Grade G2.5 is unachievable in field conditions
The process:
- Mount the rotor on the machine
- Low-speed balancing (500–1000 rpm)
- High-speed balancing (up to operating speed)
- Check the residual imbalance
- 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