How on-site oxygen generators use compressed air
Most on-site oxygen generators in hospitals, small industrial plants, aquaculture, water treatment and glass or metal work use pressure swing adsorption (PSA) with zeolite molecular sieve. Compressed air enters a bed in which the zeolite adsorbs nitrogen, letting oxygen-enriched gas pass. When the bed nears saturation, the unit switches to a second bed and vents the first to release the nitrogen. Larger plants may use vacuum pressure swing adsorption (VPSA), fed by a low-pressure blower and regenerated by a vacuum pump rather than by a compressor at several bar.
PSA oxygen typically delivers around 90–95 percent oxygen, with argon making up much of the balance, because zeolite does not separate argon from oxygen well. The air demand per unit of oxygen is high, so the air system is usually the largest energy user and the commonest source of performance problems. Zeolite is also strongly attracted to water: once wetted or contaminated with oil, its capacity can fall permanently.
Three separate acceptance decisions
An oxygen installation joins three systems that are approved on different evidence. Keeping them apart avoids the dangerous assumption that one good result proves everything.
| Decision | Who is normally responsible | Evidence that supports it |
|---|---|---|
| Feed air meets the generator inlet specification | Air-system supplier and site utility team | Measured pressure, flow, dew point, temperature, oil and particle content at the generator inlet |
| Generator delivers the stated oxygen purity, flow and pressure | Generator supplier | Calibrated oxygen analyser readings, product flow and pressure, alarm tests |
| Oxygen-side equipment and gas use are suitable | Generator supplier, oxygen-system designer and the user’s quality or medical authority | Oxygen-compatible materials and cleanliness, applicable medical or industrial gas standards, product approval |
A good dew-point reading does not prove an oxygen valve is clean for oxygen service. A good purity reading does not prove the feed air is free of oil that is slowly degrading the sieve. Medical oxygen in particular is governed by its own pharmacopoeia and hospital-gas standards and by the regulator, which sit outside the compressed-air scope.
Feed-air requirements to obtain from the maker
- Inlet pressure range at the generator connection; many compact PSA oxygen units run at a few bar to around 7–8 bar (roughly 60–115 psig). Confirm the exact range for your model.
- Feed-air flow at your required oxygen flow and purity, with its reference conditions.
- Pressure dew point; refrigerated drying (typically about +3 °C PDP) is common, and some units specify desiccant drying or include their own dryer.
- Oil content limit and whether activated-carbon filtration is required.
- Particle filtration class and maximum inlet temperature.
- Air receiver volumes recommended before and after the generator.
For VPSA plants the feed is a low-pressure blower rather than a compressor; the same principles of filtration, temperature control and steady supply apply, with the vacuum pump as an additional critical machine.
Designing the air supply step by step
- Define the oxygen duty. Purity, flow, delivery pressure, hours of use and the consequence of an interruption. For hospitals, the back-up arrangement (cylinder manifold or liquid oxygen) is part of the design.
- Obtain feed-air data at that duty. Flow and minimum inlet pressure at your purity and summer ambient temperature.
- Choose the compressor type. Oil-free compressors remove oil at source and are often preferred for oxygen duties; oil-injected screws can be used where the maker permits, with coalescing and activated-carbon filtration that is strictly maintained.
- Add treatment. Aftercooler and separator, wet receiver, coalescing filters, dryer, carbon filter where required, particulate after-filter, dry receiver.
- Allow for losses. Filter and dryer pressure drop and any dryer purge, which on a heatless desiccant dryer takes a significant share of the dried air.
- Plan redundancy. Duty and standby compressors, dryers with bypass and isolation, and an alarm when inlet pressure or dew point drifts.
Set the compressor discharge pressure only as high as the generator inlet plus losses requires. About 7 percent more power is used for every extra bar, and on a machine running continuously this adds up quickly in kWh.
Why oil and water control matter more here
Oil aerosol and vapour coat zeolite and reduce its adsorption capacity. Water is preferentially adsorbed by zeolite and displaces nitrogen capacity. Both lead to falling purity that can look like a generator fault. Beyond performance, oxygen-enriched gas raises the fire risk of hydrocarbons; this is why oxygen-side components require oxygen-compatible materials and cleaning, and why oil management on the air side deserves discipline.
- Change coalescing and carbon elements on time; do not wait for a pressure-drop alarm alone, because carbon saturation does not raise differential pressure.
- Check condensate drains daily on critical installations and after power cuts.
- Monitor dew point continuously where possible and alarm on drift.
- Locate the compressor intake away from vehicle and diesel generator exhausts and solvent stores.
Investigating a purity or feed excursion
When purity drops or the generator alarms, work through the air side methodically before opening the separation package.
| Observation | Probable cause | Check |
|---|---|---|
| Purity low only at peak oxygen demand | Inlet pressure sags during bed pressurisation | Trend inlet pressure over several cycles; review receiver size and compressor control band |
| Purity falling slowly over weeks | Moisture or oil reaching the sieve | Dryer dew point, drain operation, filter element dates, oil carry-over |
| Problems on hot afternoons | High inlet temperature, dryer overloaded | Room ventilation, dryer inlet and outlet temperatures |
| Sudden fall after power cut | Drain stuck, dryer slow to recover, valve left in bypass | Valve positions, dryer status, condensate in filters |
| Compressor cycling rapidly | Insufficient storage for pulsed demand | Receiver volume and pressure settings |
Record what was found, the corrective action and the readings after the fix. If contamination is suspected, the generator supplier should assess whether the sieve needs replacement; restoring good feed air will not always recover a damaged bed.
Maintenance routine for the air side
An oxygen generator is only as dependable as the routine that keeps its feed air in specification. A practical schedule for a hospital or plant installation includes the following, adjusted to the makers’ manuals and running hours.
- Daily: check compressor and dryer alarms, drain operation, inlet pressure at the generator and the dew-point indication if fitted.
- Weekly: inspect filter differential-pressure gauges, look for condensate in filter bowls and confirm standby compressor readiness by a short run.
- Monthly: clean intake filters and room ventilation openings, especially in the dry, dusty months, and review the pressure and purity log for drift.
- At the stated intervals: change coalescing, carbon and particulate elements, service the compressor, check dryer refrigerant or desiccant condition and calibrate the dew-point sensor.
- After any power cut or breakdown: confirm drains, dryer status and valve positions before returning the generator to full output.
Keep a simple record of readings, element changes and alarms. When purity issues arise, this history usually points to the cause faster than any single test, and it gives the generator supplier the evidence they need if the sieve must be assessed.
Plan replacement elements and service kits in advance, matched to the compressor and filter models, so that a change is never postponed for lack of a part.
Indian conditions: heat, dust and power
Hospitals and plants in Telangana and Andhra Pradesh face summer ambient temperatures of 40–45 °C, and above 45 °C on open sites, dust during dry months and humid monsoon air. These conditions raise compressor discharge temperatures, load the dryer with more water and warm the air reaching the generator. Give the compressor room proper ventilation, select dryers for the real inlet and ambient temperatures, and keep intake filters clean. Where power quality is variable, confirm automatic restart behaviour and that the oxygen receiver and back-up supply bridge any gap.
How Reddy Compressors helps
We handle the compressed-air side of oxygen installations as an independent multi-brand specialist, working alongside the generator supplier rather than replacing them. Our office is at Tarnaka, Secunderabad, and our service team of more than 20 service engineers and technicians covers all of Telangana and Andhra Pradesh, with equipment and spares supplied across India.
- Supply of new and used/refurbished oil-free and oil-injected compressors from ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic and other makes, sized from the generator’s feed-air data.
- Dryers, filters, receivers and drains matched to the inlet specification.
- Air audits measuring pressure, flow and dew point at the generator inlet.
- Service and AMC for the compressors and treatment train, including filter and drain maintenance.
- Rental compressors, including oil-free units, from our own fleet for breakdowns, shutdowns or commissioning.
- Generator power back-up through Reddy Generators, under the same management.
Oxygen-side materials, cleaning for oxygen service and product-gas approval remain with the generator supplier, the oxygen-system designer and the user’s authority.
What to send us
- Oxygen generator make, model, type (PSA or VPSA) and inlet specification.
- Required oxygen purity, flow, delivery pressure and duty hours.
- Nameplate photos of existing compressors, dryers and filters.
- Pipework sketch with receiver sizes and filter positions.
- Recent purity, pressure and dew-point readings and when issues occur.
- Site location, room size and ventilation arrangement.
Frequently asked questions
What compressor is best for a PSA oxygen generator?
The right choice is the one that meets the generator maker’s inlet pressure, flow and quality specification reliably. Oil-free screw or scroll compressors are often preferred because they remove oil at source. Oil-injected screws are used where the maker allows, provided coalescing and activated-carbon filtration are fitted and maintained. Always add a suitable dryer, receivers and a standby arrangement for critical oxygen.
Why is my oxygen concentrator purity dropping?
Common causes are low inlet pressure during bed switching, moisture from a failed drain or overloaded dryer, oil reaching the zeolite, and hot inlet air. Measure pressure, dew point and temperature at the generator inlet over several cycles. A slow decline over weeks usually indicates contamination of the sieve, which may need assessment by the generator supplier.
What dew point is needed for an oxygen generator?
Zeolite is very sensitive to moisture, so the maker’s inlet specification decides. Many PSA oxygen units accept refrigerated-dryer air with a pressure dew point around +3 °C plus filtration, while others call for desiccant drying to −20 °C or −40 °C or include an internal dryer. Monitoring dew point continuously helps catch dryer problems before purity falls.
Can an oil-injected compressor supply a medical oxygen plant?
Some generator makers permit it with specified coalescing and activated-carbon filtration, but medical installations must also satisfy hospital-gas standards and regulatory approval for the product. Many hospitals choose oil-free compressors to reduce risk. Follow the generator supplier’s written specification and your medical-gas authority’s requirements; compressed-air quality is only one part of the approval.
How big an air receiver does an oxygen generator need?
PSA units draw air in pulses as beds pressurise, so a receiver close to the generator inlet is needed to hold pressure and stop the compressor short-cycling. The generator maker usually recommends a volume. We check it against the compressor’s capacity, control band and the measured pressure dip during cycling, and size wet and dry receivers accordingly.
Does good feed air guarantee medical-grade oxygen?
No. Correct feed air is necessary for the generator to reach its rated purity, but product oxygen quality is verified separately with calibrated analysers, and medical use requires compliance with the applicable pharmacopoeia, hospital-gas standards and regulatory approval. Oxygen-side materials and cleanliness are also separate checks owned by the generator supplier and system designer.
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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.