Flashback Arrestors & Check Valves
In a flashback, the flame burns back inside the torch and can race through the hose toward the regulator and cylinder. Check valves and flashback arrestors are small, cheap devices that stop it. They should be on every oxy-fuel outfit.
- Welders & fabricators
- Pipefitters
Photo: flashback arrestors installed on the outlets of oxygen and acetylene regulators
Backfire vs. flashback
| Backfire | Flashback | |
|---|---|---|
| What happens | Flame goes out with a loud pop, or pops back into the tip briefly | Flame burns back inside the torch and can travel into hoses |
| Signs | Pop or bang; flame may relight | Squealing or hissing, smoke or soot at the torch, hot torch handle |
| Danger | Usually minor, but a warning sign | Can burn through hoses and reach regulators and cylinders |
The devices
- Check valve: lets gas flow only in the normal direction, preventing oxygen and fuel from mixing in the hoses.
- Flashback arrestor: stops a flame from passing through. Most also include a check valve, and some have a thermal shutoff.
- Where: commonly at the regulator outlets, and often also at the torch inlets. Follow the maker’s instructions.
Common causes of flashback
- Wrong gas pressures, especially oxygen pressure much higher than fuel
- Not purging hoses before lighting
- Leaks at connections or in hoses
- Clogged or damaged tips
- Kinked or pinched hoses
- Holding the tip too close to the work
- Overheated tips
If you hear squealing or hissing at the torch, close the torch valves immediately as your equipment maker instructs, then close the cylinder valves. Let the torch cool and find the cause before relighting.
After a flashback
- Inspect the torch, hoses, check valves and arrestors before using them again.
- Replace any hose that was burned inside or damaged.
- Replace or test flashback arrestors as the maker requires; many must be replaced after a flashback.
- Fix the cause before relighting.
Maintenance
Flashback arrestors and check valves wear out and can stick. Test or replace them on the schedule the maker sets, often yearly, and whenever you suspect a problem.
Standards & references
- 29 CFR 1910.253: Oxygen-fuel gas welding and cutting
- See also: Oxy-Fuel Torch Setup & Shutdown · Compressed Gas Cylinders
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