For most oxy-acetylene work, set acetylene between 3 and 8 PSI and oxygen between 10 and 40 PSI, depending on whether you’re cutting, welding, or brazing. The exact numbers depend on your tip size and the thickness of the metal you’re working with, but one rule never changes: acetylene must never exceed 15 PSI at the regulator.
Cutting Pressure Settings by Metal Thickness
Oxy-fuel cutting requires higher oxygen pressure than welding or brazing because the oxygen jet is what actually does the cutting. Acetylene stays relatively low and consistent across all thicknesses. Here are standard settings based on American Torch Tip charts for common steel thicknesses:
- 1/8″ steel: Oxygen 20–25 PSI, acetylene 3–5 PSI (tip size 000)
- 1/4″ steel: Oxygen 20–25 PSI, acetylene 3–5 PSI (tip size 00)
- 3/8″ steel: Oxygen 20–30 PSI, acetylene 3–5 PSI (tip size 0)
- 1/2″ steel: Oxygen 30–35 PSI, acetylene 3–5 PSI (tip size 0)
- 3/4″ steel: Oxygen 30–35 PSI, acetylene 3–5 PSI (tip size 1)
- 1″ steel: Oxygen 35–40 PSI, acetylene 3–6 PSI (tip size 2)
Notice the pattern: as the metal gets thicker, you step up the oxygen pressure and move to a larger tip size. Acetylene barely changes. It’s only there to maintain the preheat flame, while the high-pressure oxygen stream oxidizes and blows through the steel.
Brazing and Soldering Settings
Brazing copper pipe and fittings calls for a different balance. You’re not cutting through metal or creating a fusion weld. You’re heating a joint evenly so filler metal flows into it. For standard copper work with tip sizes 1 through 4 (covering 1/4″ up to about 1-1/8″ pipe), set acetylene to 6–8 PSI and oxygen to 10–14 PSI.
For larger copper, 1-3/8″ and above, switch to a rosebud heating tip. A rosebud spreads heat across a wider area, which you need to bring bigger joints up to temperature without overheating one spot. With a rosebud, bump acetylene to 5–7 PSI and oxygen to 15–20 PSI, adjusting upward depending on the rosebud’s size.
Why Acetylene Must Stay Below 15 PSI
Acetylene is chemically unstable at pressures above 15 PSI. At that threshold, the gas can spontaneously decompose, ignite, or detonate without any external spark or flame. This isn’t a soft guideline. It’s a hard physical limit of the gas itself.
Inside the cylinder, acetylene is dissolved in acetone and packed into a porous filler material, which stabilizes it enough to store at higher pressures. But once the gas leaves the cylinder and passes through your regulator, that stabilization is gone. The 15 PSI ceiling applies to the working pressure at the regulator’s delivery gauge, not the cylinder pressure. Every regulator, every hose, every connection downstream of the tank must stay at or below 15 PSI.
Compensating for Long Hose Runs
The pressures listed above assume a standard hose length, typically 25 feet or less. If you’re running longer hoses to reach a work area, pressure drops between the regulator and the torch tip. The fix is straightforward: increase the regulator pressure to compensate for the drop so the tip still receives the correct delivery pressure.
The critical thing to remember is that even when compensating for hose length, your acetylene regulator must not exceed 15 PSI. If your hose run is so long that you’d need to push past that limit, shorten the hose or move the cylinders closer to the work.
How to Set Pressure Safely
Getting the pressure dialed in is part of a specific startup sequence. Skipping steps or doing them out of order creates real hazards, from flashbacks to regulator damage.
Before Lighting
Start with both regulator pressure adjustment screws fully backed out (turned counterclockwise until loose). Confirm both torch valves are closed. Then slowly open each cylinder valve separately. The high-pressure gauge on each regulator will climb to show tank pressure, but no gas flows to the torch yet because the adjustment screws are backed out.
Now turn each regulator’s adjustment screw clockwise to set your working pressure on the delivery gauge. Open and close each torch valve briefly to fine-tune the pressure under flow. If you’re cutting, depress the cutting lever while adjusting oxygen pressure, since that lever opens a separate high-flow oxygen valve that affects the reading.
Lighting the Torch
Purge both lines separately by briefly opening each torch valve to blow out any mixed gases in the hoses. Then open the fuel gas (acetylene) valve about half a turn and light it with a striker. Once the acetylene flame is burning, open the oxygen valve on the torch and adjust until you get a neutral flame, where the inner cone is well-defined with no feathery acetylene excess and no harsh, pointed oxidizing appearance.
Shutting Down
Close the oxygen torch valve first, then the acetylene torch valve. For short breaks, that’s sufficient. If you’re done for the day or storing the equipment, also close both cylinder valves, then open each torch valve separately to bleed the remaining pressure from the lines. Watch both regulator gauges drop to zero. Finally, back out both regulator adjustment screws so they’re fully loose. Leaving pressure loaded on a regulator during storage wears out the diaphragm and can cause creep, where pressure slowly builds in the hose while nobody is watching.
Getting Your Flame Right
Correct regulator pressure gets gas to the tip, but the final adjustment happens at the torch valves. A neutral flame is the default for most steel work. You’ll see a bright inner cone surrounded by a darker outer envelope, with no acetylene feather extending beyond the cone tip. If you see that feather, you have too much acetylene relative to oxygen, called a carburizing flame, which deposits carbon into the weld. If the inner cone shrinks to a small, noisy, pointed shape, you have excess oxygen, an oxidizing flame, which makes steel brittle.
For brazing, a slightly carburizing flame (with a small feather) is sometimes preferred because it reduces the chance of oxidizing the base metal and interfering with filler flow. For cutting, you set a neutral preheat flame first, then the cutting oxygen lever delivers the separate high-pressure stream that does the actual work.