An acetylene burner is a gas-burning device that mixes acetylene (C2H2) with air or pure oxygen and ignites the stream at a controlled nozzle to produce a high-temperature flame. Edmund Davy first isolated acetylene in 1836, and by the early 1900s engineers like Edmond Fouché had paired it with oxygen to build the oxy-acetylene torch. The burner meters fuel and oxidiser, mixes them, and shapes the flame at the tip. With pure oxygen the flame hits roughly 3,100 °C — hot enough to weld, cut, and braze steel.
Operating Principle of the Acetylene Burner
An acetylene burner is doing three jobs at once: meter the fuel gas, meter the oxidiser, and shape the resulting flame. Acetylene leaves the cylinder dissolved in acetone at around 250 psi and steps down through a regulator to roughly 5–15 psi at the torch. Oxygen comes in separately at 15–60 psi depending on tip size. The two streams meet inside the mixing chamber of the torch handle, then exit through a copper tip with a calibrated orifice. Light it, adjust the oxygen until the inner cone is sharp and bright blue with no feather of unburned carbon, and you have a neutral flame at about 3,100 °C.
The flame structure matters. You see three zones — the inner cone where acetylene cracks into carbon and hydrogen, the intermediate reducing zone where C2H2 + O2 → 2CO + H2, and the outer envelope where those products finish burning in atmospheric oxygen to CO2 and water vapour. A carburizing flame (excess acetylene) shows a feathery secondary cone and is what you want for hardfacing or welding high-carbon steel. An oxidizing flame (excess oxygen) burns shorter, sharper, and hisses — useful for brazing brass, dangerous for steel. The neutral flame sits in between and is the workhorse setting.
Get the tip orifice wrong and the burner misbehaves fast. Drill a #56 tip oversize and the gas velocity drops below the flame propagation speed, the flame walks back into the mixing chamber, and you get a flashback — the bang is unmistakable. Run pressures too low and the same thing happens. That is why every modern oxy-acetylene rig has a flashback arrestor at both the torch inlet and the regulator outlet. If you notice the flame popping, snapping, or burning yellow, stop — the tip is either dirty, oversized from a tip cleaner, or your acetylene pressure is below 5 psi where the gas itself becomes unstable.
Key Components
- Fuel Regulator: Steps acetylene cylinder pressure down from up to 250 psi to a working 5–15 psi at the torch. Never run acetylene above 15 psi — above that pressure the gas becomes shock-sensitive and can decompose explosively without any oxygen present.
- Mixing Chamber: Combines metered acetylene and oxygen inside the torch handle just upstream of the tip. The chamber geometry sets the gas velocity — too slow and the flame flashes back, too fast and the flame blows off the tip.
- Tip / Nozzle: Copper or copper-alloy nozzle with a precision-drilled orifice sized for a specific flow rate. A #1 tip flows roughly 1 SCFH of acetylene; a #8 tip flows about 35 SCFH. The orifice must stay round — clean with a tip cleaner of the matching wire size, never a drill bit.
- Flashback Arrestor: Sintered metal element that quenches a returning flame before it reaches the regulator or cylinder. Required by OSHA on commercial rigs. If yours has ever stopped a flashback, replace it — the element fuses internally after a single event.
- Check Valves: Spring-loaded one-way valves that prevent oxygen from migrating into the acetylene line or vice versa. Reverse flow inside the hose is the most common cause of hose explosions on poorly maintained rigs.
- Cylinder with Acetone: Acetylene cylinders are packed with a porous mass (calcium silicate or similar) saturated with acetone. The acetone dissolves up to 25 volumes of acetylene per volume of acetone at 250 psi, allowing safe storage. Always use cylinders upright — laying one on its side lets acetone migrate to the valve and contaminate the torch.
Industries That Rely on the Acetylene Burner
Acetylene burners cover everything from a single-jet carbide miner's lamp to industrial cutting torches that slice 12-inch steel plate. The reason it has stuck around despite cheaper alternatives like propane is simple — no other commonly available fuel gas matches the flame temperature with pure oxygen, and no other gas delivers the sharp inner cone that lets a welder concentrate heat into a tight puddle. If you are doing precision work on thin steel, brazing brass tubing, or cutting structural members in the field with no electricity, acetylene is still the answer.
- Metal Fabrication: Victor Technologies and Harris oxy-acetylene welding torches used for thin-gauge steel sheet metal, automotive body work, and aircraft tubing repair on Cessna and Piper airframes.
- Steel Cutting: ESAB cutting torches with rosebud or cutting tips used in shipbreaking yards and structural steel demolition where 100–300 mm plate must be severed without electrical power.
- Glassworking: Carlisle Mini CC and Nortel Red Max bench burners running oxy-acetylene for borosilicate scientific glassblowing and Pyrex laboratory apparatus fabrication.
- Mining and Caving: Justrite carbide lamps using calcium carbide and water to generate acetylene on demand — still used by cave explorers because the wide flame illuminates passages better than LEDs.
- Jewellery and Brazing: Smith Little Torch with #3 and #4 tips for silver soldering, gold brazing, and precision platinum work where flame size needs to drop below 6 mm.
- Atomic Absorption Spectroscopy: PerkinElmer and Agilent AA spectrometers using premixed air-acetylene burners with a 100 mm slot to atomise samples for trace metal analysis at roughly 2,300 °C.
The Formula Behind the Acetylene Burner
The core calculation for any acetylene burner is the heat output, which is fuel flow rate multiplied by the heating value of acetylene. This sets your tip selection. At the low end of the typical range — a #0 tip flowing 1 SCFH — you have enough heat to braze 0.5 mm jewellery wire and not much more. At the nominal middle of the range, around 10–20 SCFH on a #4 or #5 tip, you cover most general welding and brazing on 1.5–6 mm steel. At the high end, a rosebud heating tip flowing 100+ SCFH can preheat a 200 mm casting before welding. The sweet spot for most shop work sits at 8–20 SCFH where the flame is hot enough to weld but the gas consumption stays economical.
Variables
| Symbol | Meaning | Unit (SI) | Unit (Imperial) |
|---|---|---|---|
| Q | Heat output of the flame | kW | BTU/hr |
| ṁC2H2 | Mass or volumetric flow rate of acetylene through the tip | kg/s or m³/s | lb/hr or SCFH |
| HVC2H2 | Heating value of acetylene (lower heating value) | 48.2 MJ/kg | 1,470 BTU/SCF |
Worked Example: Acetylene Burner in selecting a tip for a Victor J-100 torch
You are setting up a Victor J-100 oxy-acetylene torch to weld 3 mm mild steel plate in a small fabrication shop. The manufacturer recommends a #2 tip flowing roughly 5 SCFH of acetylene. You want to know the heat output at that nominal setting, and how it compares to the #0 tip you might use on thinner stock and the #5 tip you would swap in for 6 mm plate.
Given
- ṁnom = 5 SCFH
- ṁlow = 1 SCFH
- ṁhigh = 20 SCFH
- HVC2H2 = 1,470 BTU/SCF
Solution
Step 1 — at the nominal #2 tip flowing 5 SCFH, compute heat output:
That is about 2.15 kW of fuel heat — enough to puddle 3 mm mild steel cleanly with a tight inner cone. The weld pool stays controllable and you can run a 100 mm bead without overheating the surrounding metal.
Step 2 — at the low end of the typical range, a #0 tip flowing 1 SCFH:
That is a pencil-flame burner — appropriate for jewellery work and 0.5–1 mm sheet, but try to weld 3 mm plate with it and the heat dissipates into the parent metal faster than you can build a puddle. You will sit there for 30 seconds watching nothing happen.
Step 3 — at the high end, a #5 tip flowing 20 SCFH:
This is the territory for 6 mm plate and structural work. The flame is loud, the inner cone is roughly 12 mm long, and the puddle forms in 2–3 seconds. Push a #5 tip onto thin sheet and you will burn through before you can move the torch.
Result
Nominal heat output is 7,350 BTU/hr (2. 15 kW) at the #2 tip — the standard setting for 3 mm mild steel. Low-end at 1,470 BTU/hr is too cold for anything beyond jewellery and aircraft tubing, while the high-end 29,400 BTU/hr at a #5 tip is in heavy-plate territory. The sweet spot for general shop work sits between the #2 and #4 tips, 5–10 SCFH. If your measured weld penetration is shallow despite using the right tip, suspect three causes in this order: (1) acetylene regulator drooping below 5 psi under flow, which starves the tip — check static vs. dynamic pressure with the torch open; (2) tip orifice oxidised or carbon-fouled, dropping effective flow by 20–30 % — clean with the matched tip cleaner wire, not a drill; (3) oxygen pressure set too low for the tip number, giving a soft carburizing flame instead of neutral — the inner cone goes feathery and the heat input drops noticeably.
Choosing the Acetylene Burner: Pros and Cons
Acetylene is not the only fuel gas in the shop. Propane, MAPP-substitute (now mostly propylene blends), and hydrogen all compete for similar jobs. The choice comes down to flame temperature, fuel cost, and whether you need to cut, weld, or just heat.
| Property | Acetylene Burner | Propane Burner | Hydrogen Burner |
|---|---|---|---|
| Peak flame temperature with O2 | ~3,100 °C | ~2,800 °C | ~2,660 °C |
| Heating value | 1,470 BTU/SCF | 2,500 BTU/SCF | 325 BTU/SCF |
| Suitable for fusion welding steel | Yes | No — flame too cold and too oxidising | Marginal — used for aluminium and lead |
| Cutting performance on thick steel | Fast preheat, fastest pierce | Slower preheat but cheaper for long cuts | Rare in cutting service |
| Fuel cost per BTU delivered | High | Low (≈ 1/3 of acetylene) | Very high |
| Cylinder safety | Must stay upright, max 15 psi working | Liquid LPG, no orientation limit | Compressed gas, embrittlement concerns |
| Typical applications | Welding, brazing, cutting, AAS | Heating, soldering, propane cutting torches | Underwater cutting, atomic spectroscopy |
Frequently Asked Questions About Acetylene Burner
Popping with a brief flashback usually means gas velocity at the tip dropped below the flame propagation speed of the C2H2/O2 mixture (around 10 m/s for a neutral mix). The two non-obvious causes are a partially blocked tip orifice — even a 10 % carbon deposit drops mass flow enough to let the flame walk back — and an acetylene cylinder that has been stored on its side, allowing acetone to slug into the regulator and intermittently choke flow.
Diagnostic check: shut off, clean the tip with the correct numbered cleaner wire, stand the cylinder upright for 30 minutes, and re-light. If it still pops, the flashback arrestor itself may have partially fused from a prior event and needs replacement.
The neutral flame has a single sharp blue inner cone with no feather around it. A carburizing flame shows a faint secondary feather extending 3–10 mm beyond the inner cone — that feather is unburned acetylene. Adjust the oxygen valve up slowly and watch the feather collapse into the inner cone. The instant the feather disappears, you are neutral. Add another 1/8 turn of oxygen and you tip into oxidising — the cone gets shorter, sharper, and the flame starts to hiss audibly.
For steel welding, set neutral and leave it. For hardfacing rod or high-carbon steel, back off oxygen until you see a 2–3 mm feather.
Depends on the cut volume. Acetylene preheats faster — about 30 % less time to reach the kindling temperature of steel — and pierces thick plate quicker, so for short cuts and frequent piercing it wins. Propane is cheaper per BTU and burns cooler, so on long continuous cuts through 25–50 mm plate where preheat time amortises across a long bead, propane saves money.
The catch: propane requires different tips (designed for the heavier gas density and lower flame speed) and a higher oxygen flow. Do not just swap the cylinder — swap the tip and re-set the regulators. Mixing acetylene tips with propane gives weak preheat and a slag-laden cut.
Cylinder gauge pressure does not tell you how much gas is left or available — acetylene is dissolved in acetone, and you cannot pull more than about 1/7 of the cylinder contents per hour without dragging acetone along with the gas. If you are running a large rosebud at 30+ SCFH off a small MC cylinder, you are exceeding the safe withdrawal rate, the dissolved gas cannot evolve fast enough, and the regulator droops under load.
The fix is either a larger cylinder (a #4 or #5 industrial size) or a manifolded pair of cylinders. As a rule of thumb, never withdraw more than 1/7 of the cylinder volume per hour continuously.
Almost certainly yes. Brass contains zinc, which boils at 907 °C — well below the brazing temperature. A neutral or carburizing flame on brass volatilises the zinc, leaving porosity and a dull grey skin on the joint. You need a slightly oxidising flame, which forms a thin zinc-oxide film that suppresses further zinc loss.
Set neutral, then add 1/8 turn of oxygen until the inner cone shortens noticeably and the flame starts to hiss. The joint will come out clean and shiny. This is the one case where oxidising flame is correct on a fluxed joint — counterintuitive, but it is in every brass-brazing manual for a reason.
No, and this is where people get hurt. Acetylene tips have a small recess and tight orifice sized for the high flame speed of C2H2 (~7.5 m/s laminar). Propane has a flame speed of about 3.7 m/s and requires a deeper recess and different orifice geometry to prevent the flame from sitting on the metal of the tip and overheating it. Use an acetylene tip with propane and the flame parks on the tip face, melts the copper, and drops molten metal into your work — or the tip itself ignites.
Buy propane-specific cutting and heating tips. Most major brands (Victor, Harris, Smith) mark them clearly with an LP or HPN suffix.
Dragline slag means the cutting oxygen is not reaching the bottom of the kerf with enough velocity to blow molten iron-oxide clear. Three real-world causes: the cutting oxygen pressure is too low for the tip and plate thickness (a #2 cutting tip on 25 mm plate wants 40+ psi of cutting O2), the tip is held too far from the work — the preheat cones should sit 2–3 mm above the surface, no more — or you are travelling too fast and the cut cannot keep up.
Slow down to where the sparks shower vertically downward through the kerf rather than trailing behind the tip. If they still trail, raise the cutting oxygen pressure 5 psi and try again.
References & Further Reading
- Wikipedia contributors. Oxy-fuel welding and cutting. Wikipedia
Building or designing a mechanism like this?
Explore the precision-engineered motion control hardware used by mechanical engineers, makers, and product designers.
