How an air bearing uses compressed air
An aerostatic air bearing floats a moving part on a thin film of pressurised air, typically only a few microns thick. Air enters through small orifices, porous media or grooves and escapes at the edges. Because there is no contact, there is almost no friction, no wear and very smooth motion, which is why air bearings are used in coordinate measuring machines, precision stages, spindles, wafer and display handling, optical inspection and test equipment.
The thin film also makes the bearing intolerant of poor air. A particle larger than the gap can scratch the surface or block an orifice. Oil or water droplets can clog porous media or alter the film. A pressure dip reduces stiffness and load capacity; a total loss of air can let the surfaces touch while still moving, which can damage the bearing permanently.
What the bearing maker specifies
Every air-bearing maker publishes its own supply requirements, and these govern. There is no universal “air-bearing grade”. Typical items in a specification are:
- Supply pressure at the bearing inlet, often a few bar with a narrow allowed band.
- Flow at that pressure, which is usually small and steady per bearing but adds up across a machine.
- Filtration, commonly very fine particulate and coalescing filtration ahead of the bearing.
- Pressure dew point, often a desiccant-level dew point so no condensation can form in air-conditioned rooms.
- Oil content, frequently stated as oil-free or a very low limit.
- Air temperature and its stability, because air temperature changes affect thermal stability of precision machines.
- Pressure ripple or stability limits, and start-up and shutdown sequencing.
Express the plant-side target in ISO 8573-1 terms where possible, but do not assume a class number on its own captures every requirement, for example ripple, temperature or the shutdown sequence.
Supply architecture for precision air
| Element | Purpose | Good practice |
|---|---|---|
| Compressor | Source of air | Oil-free compressor, or oil-injected with verified multi-stage filtration; duty and standby for critical machines |
| Dryer | Remove water vapour | Desiccant dryer at typical −40 °C PDP where the bearing maker requires low dew point; refrigerated at typical +3 °C only if documented as acceptable |
| Main filtration | Remove particles and oil aerosol | Coalescing before the dryer, dust filter after; carbon stage if oil vapour is limited |
| Distribution | Carry clean air to the machine | Corrosion-resistant pipe (aluminium or stainless), no dead legs, take-offs from the top of headers |
| Local receiver | Buffer demand changes and supply interruptions | Sized to support controlled stop of the machine on loss of supply |
| Point-of-use filtration | Final protection at the machine | Fine particulate and coalescing filters close to the bearing, with differential pressure indication |
| Precision regulator | Hold the bearing pressure steady | Dedicated regulator for the bearing circuit, not shared with valves or blow-offs |
| Monitoring | Detect loss before damage | Pressure switch or transducer interlocked to the machine; dew point monitoring on critical lines |
Why pressure stability matters more than pressure level
Air-bearing stiffness and lift depend on supply pressure. If the same header supplies blow-off nozzles, cylinders or tools, their demand surges cause pressure dips that reach the bearing. In a measuring machine this can appear as a repeatability or accuracy problem rather than an obvious air fault.
- Feed the bearing circuit from its own branch with a check valve and local receiver, so other users cannot draw it down.
- Set the main system pressure above the bearing regulator setting by enough margin to keep the regulator in control during header dips.
- Avoid unstable compressor control bands reaching the machine; the regulator and receiver should flatten them.
- Record pressure at the bearing inlet during the heaviest motion and while other plant users are at peak, not only at idle.
Measuring what the bearing actually receives
- Identify the bearing maker’s limits for pressure, flow, filtration, dew point, oil and temperature.
- Fit a test point immediately upstream of the bearing manifold.
- Log pressure with a fast-responding transducer through a full machine cycle and during known plant upsets, such as compressor changeover or a large user starting.
- Measure pressure dew point at the machine, not only at the dryer outlet.
- Where oil or particles are a concern, arrange sampling to ISO 8573 methods at the point of use.
- Check point-of-use filter differential pressure and drain condition.
- Compare results with the documented limits and record the outcome.
Measuring at the compressor room only tells you what left the plant room. Piping corrosion, poor drains and dead legs can all change the air before it reaches the machine.
Common problems and their causes
| Symptom | Likely air-side causes |
|---|---|
| Reduced accuracy or repeatability | Pressure ripple from shared users, temperature swings in supply air |
| Bearing sticking or scoring | Loss of supply while moving, particles, oil or water reaching the gap |
| Rising bearing flow over time | Wear or damage, or a regulator setting drifting upward |
| Falling flow and lift | Partially blocked orifices or porous media from oil, water or dirt |
| Frequent filter element changes | Poor upstream treatment, corroded pipework, oil carry-over from the compressor |
| Machine alarms on start-up | Air not established before motion, receiver not charged, sequencing fault |
Continuity, standby and shutdown
For a precision machine, a short air interruption can be far more expensive than the air itself. Plan what happens on loss of supply:
- Interlock the machine so motion stops when bearing pressure falls below the maker’s minimum.
- Provide a local receiver with a check valve to allow a controlled stop.
- Run duty and standby compressors and dryers on critical lines, with automatic changeover.
- Plan maintenance so filter and dryer work does not interrupt supply; bypass lines must not bypass treatment.
- Keep a rental compressor and dryer option ready for planned shutdowns and breakdowns. In Hyderabad’s summer, power fluctuations and high ambient temperatures make this more than a theoretical risk.
Estimating the air demand of a precision machine
Individual air bearings use small, steady flows, but a measuring machine or stage may have many pads, plus counterbalance cylinders, clamping and cleaning blow-offs. Add the bearing maker’s flow at the set pressure for every bearing, then add the other users on the same machine with their own duty. Convert the total to free air at the compressor’s reference conditions and add a margin for wear, because bearing flow tends to rise as surfaces and restrictors age.
The flow is small enough that compressor size is rarely the problem. The usual difficulty is delivering that small flow with the required cleanliness and stability through a plant system that also feeds large, fluctuating users.
Where precision air is used in India
Air bearings and precision air support are found in quality laboratories with coordinate measuring machines, electronics and semiconductor assembly, solar cell and display handling, precision machining spindles, aerospace and defence component inspection, and laboratory instruments. In Hyderabad and Telangana these sit alongside pharma, defence and electronics manufacturing, where clean, dry air is already expected. Air-conditioned rooms make dew point especially important, because pipes passing through cooler areas can condense water that warmer plant air would carry as vapour.
How Reddy Compressors helps
Reddy Compressors, Tarnaka, Secunderabad, works as an independent multi-brand specialist with Atlas Copco, Ingersoll Rand, ELGi, KAESER, Chicago Pneumatic and other makes. We are not an authorised dealer of any brand, and bearing selection and machine design stay with the bearing and machine makers. We have tie-ups with all major and reputed brands. What we deliver is the air supply side:
- Supply of oil-free and oil-injected compressors, desiccant and refrigerated dryers, filters and receivers sized for the duty.
- Air-quality and pressure-stability audits at the point of use, including dew point and pressure logging.
- Service and AMC of compressors, dryers and filtration across Telangana and Andhra Pradesh by over 20 service engineers and technicians.
- Rental compressors and dryers for standby and planned shutdowns.
- Filter elements, drains and spares identified from your equipment and confirmed before quoting.
What to send us
- The machine and bearing maker, model and documented air requirements.
- Number of machines and their combined flow at working pressure.
- Existing compressor, dryer and filter details, and pipe material.
- Any measured pressure, dew point or air-quality results.
- Symptoms or alarms, and when they occur.
- Criticality of the machine and any standby requirement.
Frequently asked questions
What air quality is needed for an air bearing?
The bearing maker’s documented requirement governs. It usually calls for very fine particle filtration, oil-free or very low oil content, and a low pressure dew point so no condensation forms. These can often be expressed as ISO 8573-1 classes, but ripple, temperature and shutdown sequence also matter. Verify the air at the bearing inlet, not only at the compressor room.
Can I use an oil-injected compressor for air bearings?
Often yes, provided the air passes through correctly maintained coalescing and, where required, carbon filtration, and is dried to the required dew point, with results verified by sampling. Some makers or industries prefer oil-free compressors to remove the risk of oil carry-over altogether. Choose based on the bearing maker’s limits and the consequence of a filtration failure.
Why does my measuring machine lose accuracy when other machines start?
Other users drawing from the same header cause pressure dips that reach the bearing and change its stiffness and lift. Give the bearing circuit its own branch with a check valve, a local receiver and a dedicated precision regulator. Log pressure at the bearing inlet while the other machines start to confirm the cause.
What happens if the air supply to an air bearing fails?
The air film collapses and the surfaces can touch. If the axis is still moving, the bearing can be scored or damaged permanently. Machines should be interlocked so motion stops when bearing pressure falls below the maker’s minimum, with a local receiver to support a controlled stop and standby compressors and dryers on critical lines.
Do I need a desiccant dryer for air bearings?
In many cases yes. Air bearings often sit in air-conditioned rooms, and any condensation can block orifices or porous media. A desiccant dryer at a typical −40 °C pressure dew point removes that risk. A refrigerated dryer at a typical +3 °C dew point may be acceptable only where the bearing maker documents it and pipework never passes through cooler areas.
How often should point-of-use filters for air bearings be changed?
Follow the filter and bearing makers’ intervals and change elements earlier when differential pressure reaches the recommended limit. Log the pressure drop at each service. If elements load quickly, the problem is usually upstream: oil carry-over, a failed drain, a dryer issue or corroded pipework shedding particles, and fixing that protects both the filters and the bearing.
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Technical content reviewed by D. Srinivas Reddy, Managing Partner and service engineer, Reddy Compressors. Last updated 17 October 2026. How our engineering content is reviewed.