Used Oxygen Concentrator Guide: Buying a Secondhand Medical Unit for Lampworking
Short answer: A used home medical oxygen concentrator is one of the cheapest ways to feed a small or mid-size torch — if you buy the right kind and check the right things. You want a continuous-flow unit (never a pulse-dose portable), typically a 5 L class machine like the Philips Respironics EverFlo or Drive DeVilbiss 525, which delivers roughly 87-94% oxygen at 5-9 psi outlet pressure. Before buying, check the hours meter, watch the low-purity indicator light during a warm-up run, and understand that the zeolite sieve beds — the part that actually separates the oxygen — wear out slowly over thousands of hours and are not a user-serviceable part. One healthy 5 LPM unit will comfortably run torches like the Nortel Minor or GTT Bobcat.
This guide pairs with oxygen concentrator vs tanks (should you use a concentrator at all?) and how many LPM does my torch need (how much oxygen your specific torch drinks).
Why used medical concentrators are lampworking’s best-kept bargain
Home oxygen concentrators are built as durable medical equipment (DME): they run for years in patients’ homes, then get retired, refurbished, or sold off when a prescription ends — a steady secondhand supply of machines that make oxygen from room air, no cylinders or refills, for the cost of electricity.
How they work matters for what you’ll inspect later. These machines use pressure swing adsorption (PSA): a compressor forces filtered room air through beds of zeolite molecular sieve, which adsorb nitrogen and pass oxygen; the cycle then reverses to purge the nitrogen, and product oxygen collects in an accumulator tank (FDA consumer update; Respironics EverFlo service manual). Buying used comes down to two questions: is the compressor healthy, and how much life is left in those sieve beds?
LPM and PSI: what the ratings actually mean at your torch
A concentrator carries two numbers that matter at the bench:
- LPM (liters per minute) is volume of oxygen delivered. A “5 LPM unit” can supply up to 5 liters of ~90%-pure oxygen per minute, adjusted with the front flowmeter. This is the number you match to your torch’s appetite — see how many LPM does my torch need.
- PSI (outlet pressure) is how hard the machine pushes that oxygen out. Home units are regulated low — the EverFlo’s product tank is set to a nominal 5.5 psig, and the DeVilbiss 525’s maximum outlet pressure is 8.5 psig (per their respective service manuals). This is nothing like the pressures a tank regulator can deliver.
One number the spec sheet won’t say out loud: a concentrator’s oxygen is not 100% pure. The FDA puts home-unit output at roughly 87-94% oxygen, versus essentially pure cylinder oxygen — the DeVilbiss 525 specs 87-93% across its settings, the EverFlo 93% +/-3% at 5 LPM. Torches run fine on this; just remember it when comparing notes with tank users.
The spec that matters most: continuous flow (skip pulse-dose portables)
The single biggest filter when shopping used: the machine must be continuous flow. The FDA distinguishes two delivery modes in home oxygen equipment:
- Continuous flow: the valve stays open and the unit delivers a steady LPM stream. This is what stationary home units like the EverFlo and DeVilbiss 525 do — and it’s what a torch needs.
- Pulse dose: the unit releases a small bolus of oxygen only when it senses the patient inhaling. Portable travel concentrators use this to save battery and weight.
A torch never “inhales,” so a pulse-dose portable will sit there waiting for a breath that never comes. Those small, light, battery-powered units look tempting on the used market — pass on all of them. If the listing says “portable” or “pulse,” it is not a lampworking machine.
Output pressure: why 5-9 psi is normal and what it limits
Typical home-unit outlet pressures cluster around 5-9 psi (EverFlo 5.5 psig, DeVilbiss 8.5 psig per their service manuals). That’s not a defect — it’s the design — but it shapes your setup two ways:
- Torch choice. Concentrator-friendly torches are engineered for low-pressure oxygen. Small and mid surface-mix bench torches thrive; burners built around tank-regulator pressures starve.
- Operating habit. Keep the torch’s oxygen valve open whenever the machine is running, so the compressor isn’t dead-heading against a closed valve, and never set the flowmeter above rated LPM (D.A. Clarke, “Using a DME Oxygen Concentrator for Lampworking”; Lampwork Etc. archives).
Two benchmark 5 L machines
These two show up constantly on the used market and have public service manuals, which makes them easy to research and easy to have serviced:
| Spec | Philips Respironics EverFlo | Drive DeVilbiss 525DS |
|---|---|---|
| Flow range | 0.5-5 LPM | 0.5-5 LPM |
| Outlet pressure | 5.5 psig nominal (5.5 +/-0.25 in service) | 8.5 psig max |
| Purity spec | 93% +/-3% at 5 LPM | 87-93% across settings |
| Power draw | ~350 W | ~310 W |
| Weight | 31 lb | 37 lb |
| Purity indicator | OPI (ultrasonic) | OSD variant (low-purity light) |
(Sources: EverFlo Service & Technical manual and Philips specifications page; DeVilbiss 525 service and user manuals.)
Inspecting a used unit: hours meter, purity light, and a listening test
Always inspect running, not just “powers on.” Work through:
- Hours meter. Most units log total run hours. Lower is better, but hours alone don’t tell the whole story — sieve life also depends on the humidity the machine lived in (see below).
- Purity indicator. Many concentrators include a built-in low-purity sensor — DeVilbiss OSD, Respironics OPI (which measures output purity ultrasonically), Invacare SensO2 — that flags when concentration falls below threshold. On a used unit this is your stand-in for an oxygen analyzer: warm the machine up at rated flow and confirm the purity light stays green with no alarm. Prefer units that have one.
- Sound and airflow. A healthy unit cycles rhythmically as the sieve beds swing. Listen for compressor knocking, hissing leaks, or a unit that never settles into its cycle, and check the intake filter area is clean.
- Steady flow at the top setting. Set the flowmeter to rated maximum and confirm the ball holds there without straining or alarming.
An oxygen analyzer reading at rated flow is the definitive test, but a working factory purity sensor plus a full-flow warm-up run is a reasonable field substitute.
Sieve bed health: the slow death you can measure
The zeolite sieve beds are the consumable heart of the machine. Over thousands of operating hours the zeolite gradually loses its nitrogen-binding capacity, and moisture contamination accelerates the loss. The tell-tale symptom: the unit sounds and runs completely normally while delivered purity slowly declines at rated flow (HengYe zeolite manufacturer guides). That’s why the purity indicator matters so much on a used purchase — a worn machine passes every casual test except the one that counts.
Purity loss also isn’t uniform across the dial — it’s worst at the top of the flow range. Lampworkers report worn 5 LPM units doing around 85% at 5 LPM but ~95% at 4 LPM, and the common workaround is to run the flow ball one mark below the machine’s max (Lampwork Etc. archive threads). A tired concentrator often has years of life left at a slightly reduced setting — you’re just buying a “4 LPM machine” instead of a 5.
To slow the decline: sieve-bed guides recommend roughly 60-80 F ambient with relative humidity below ~60%, plus an annual purity/output check to catch fading beds early.
Maintenance you can do: filters, placement, humidity
User-serviceable maintenance is deliberately limited:
- External gross-particle intake filter: check roughly every 1-2 weeks and clean when visibly dirty (DeVilbiss 525 service manual; AirSep NewLife Elite patient manual).
- Clearance: keep intake and cabinet vents unblocked so the compressor breathes cool air.
- Environment: dry, moderate-temperature room — humidity is the sieve killer.
Everything else — internal HEPA/inlet filters, valves, compressor, and the sieve beds themselves — is technician-level work covered in the service manuals.
When a concentrator is dead vs just dirty
A rough triage, based on the failure modes above:
| Symptom | Likely meaning | Worth buying/fixing? |
|---|---|---|
| Weak output, filthy intake filter | Starved for air | Clean the filter and retest — often fine |
| Runs normally, purity light trips at max flow | Sieve beds fading | Usable at a lower setting; beds are a technician job |
| Purity alarm even at low flow | Sieve beds spent (or sensor fault) | Effectively dead without a rebuild |
| Compressor knocking, won’t build pressure, constant alarms | Mechanical failure | Walk away unless it’s nearly free |
A unit whose beds have truly died costs technician money to revive, and the used market is full of healthy replacements. Buy the machine with the green purity light, not the project.
Matching one 5-10 LPM unit to your torch
A single healthy 5 LPM unit is a confirmed match for the small and mid surface-mix bench torches lampworkers actually run on concentrators — community torch-comparison threads specifically list the Nortel Minor, GTT Bobcat, GTT Cricket, and small Bethlehem-class bench torches like the Bethlehem Alpha as running well on one 5 LPM machine (Lampwork Etc. “Torch Comparisons on 5 LPM Oxygen Concentrator” archive thread). Hungrier torches need a 10 LPM class unit or multiple concentrators — and at some point tanks make more sense; see oxygen tanks, suppliers, and costs for that side of the math.
The safe expectation: one 5-10 LPM machine per small-to-mid torch, run at or below rated flow, delivering ~90% oxygen at single-digit psi. Plan around that and a used concentrator will not disappoint you.
Oxygen safety rules that never bend
A concentrator is gentler than a high-pressure cylinder, but it still fills your line and exhaust path with oxygen-enriched gas. From the equipment manuals and the FDA’s home-oxygen guidance:
- Never use oil, grease, or lubricants on fittings, tubing, or connections — petroleum products can ignite spontaneously in contact with pressurized oxygen.
- Oxygen doesn’t burn, but everything else burns harder in it. Materials ignite and burn far more readily in oxygen-enriched air.
- Keep smoking and open flame away from the machine’s intake side and its enriched exhaust area — your torch flame belongs at the end of the hose, nowhere near the box.
These sit on top of your normal station practice — flashback arrestors, leak checks, ventilation — covered in the glass torch safety setup checklist. And as always: the manufacturer’s manual for your specific unit takes precedence over anything in this article.
Key takeaways
- Buy continuous-flow stationary units only; pulse-dose portables cannot feed a torch.
- Expect 87-94% purity and 5-9 psi at the outlet — normal for the class.
- Inspect running: hours meter, factory purity indicator (OSD/OPI/SensO2) green at rated flow, smooth compressor cycle.
- Sieve beds die slowly and invisibly — purity fades at max flow first; running one mark below max extends a worn unit’s life.
- Your maintenance is the external intake filter and a dry, cool room; everything internal is technician territory.
- One healthy 5 LPM unit runs a Nortel Minor, GTT Bobcat, GTT Cricket, or small Bethlehem-class torch; keep the torch oxygen valve open while the machine runs and never exceed rated LPM.
- No oil or grease near oxygen, ever, and your unit’s manual overrides any general guide.
Sources
- FDA Consumer Update, “Pulse Oximeters and Oxygen Concentrators: What to Know About At-Home Oxygen Therapy” — https://cacmap.fda.gov/consumers/consumer-updates/pulse-oximeters-and-oxygen-concentrators-what-know-about-home-oxygen-therapy
- D.A. Clarke, “Using a DME Oxygen Concentrator for Lampworking” — https://www.daclarke.org/ArsBrevis/oxyBoxen.html
- Lampwork Etc. archive, concentrator purity/flow discussion — https://www.lampworketc.com/forums/archive/index.php/t-107834.html
- Philips EverFlo home oxygen system specifications — https://www.usa.philips.com/healthcare/product/HC1020000/everflo-home-oxygen-system/specifications
- DeVilbiss 525 Oxygen Concentrator service manual — http://www.frankshospitalworkshop.com/equipment/documents/oxygen_concentrators/service_manuals/DeVilbiss%20525%20Oxygen%20Concentrator%20-%20Service%20manual.pdf
- Respironics EverFlo Service & Technical manual — https://oxygenalliance.org/wp-content/uploads/2024/03/Respironics-EverFlo-Service-Manual.pdf
- AirSep NewLife Elite patient manual — https://oxygenalliance.org/wp-content/uploads/2024/03/AirSep-NewLife-Elite-Patient-Manual.pdf
- HengYe Inc., oxygen concentrator zeolite guides — https://hengyeinc.com/oxygen-concentrator-zeolite/
Editor’s note: pressures, purity ranges, and model specs above come from the cited FDA guidance and manufacturer service manuals as of 2026, and individual units vary with age and condition. Always follow the manual for your specific concentrator and torch — it takes precedence over this guide.