twyer backfire.

[redd1981]

Hey guys my forge seems to be backfire sometimes a few seconds after I turn the air supply off. Does anyone know what is causing this?

Im guessing it has to with excess water dripping down in it and causing steam to build pressure until there is enough to get through the grate. Its not so much force that blows my charcoal out or anything and its usually not very loud but the last one was so loud the ol' lady came out to see if I was ok lol.

[HWooldridge]

It happens because the volatiles in the fuel occasionally build up combustible gas between heats.  It usually only occurs when first starting up the blower after it's been sitting a few minutes.  I'm told it can wreck a traditional great bellows but it won't do much to a blower.

[redd1981]

Ok is there anyway way to prevent this?

Just had another big one about 2 minutes ago

Its a brake rotor forge whith the basic 2" "T" configuration with a blow dryer.

I live in the county and dont want my neighbors thinking Im shooting skeet in the backyard.

[HWooldridge]

Is your ash dump a flapper or screw off?  You could open the ash dump every time you turn on the blower and it should diffuse the gas enough to stop the backfire.  Although that would be a pain with a threaded cap.

You can also leave the blower on all the time and choke the air with a damper.  A slight trickle of blast should prevent gas buildup.

[ThomasPowers]

passing steam over hot coke produces producer gas---what used to run most gas lights in Victorian cities.  It is combustible and can be explosive.  (I've never had it when using charcoal only coal---unless you are coaling wood to make charcoal then there are combustible gasses evolving)

Use less water, design your system so gas can't collect in lower areas. install a safety valve, keep a low amount of air blowing to push the gas out, etc

[Glenn]

Smoke/volitals are collecting in the air supply tube. When you give ir a fast crank of air you introduce oxygen to the smoke/volitals and when the mix hit a ignition source, BOOM. I have been next to a bellows when it went off and it sounded like a shotgun. I used to use an expandable plastic clothes dryer vent pipe at my forge until the day it went BOOM and caught 4-6 feet of the plastic pipe on fire and melted the plastic leaving just the support wire.

One way to avoid the problem is to keep a small positive air flow going through the pipe to the forge. If you using a hand crank blower or bellows, give it just a wee bit of air in order to push any collected gasses toward the fire. This is not enough air to mix with the gasses, but just enough to gently move them down the pipe. A crank or two of gentle air is enough, then you can crank at normal speed.

Keep the air source below the level of the forge. Weather also plays a part in boom or no boom.

Yes, BOOM can and WILL get your attention and your heart started. (grin)

[Quarry Dog]

I don't know about charcoal, but I've seen this happen a couple times with a coal fired forge using a hand cranked blower.

  Apparently it is most likely to happen when you're watering the edges of your fire and you aren't providing any blast.  I hear it has something to do with steam forcing volatiles down the tuyere.  

  The only things I know for sure are that I didn't do it, it shook all the dust loose in the shop, and the first time I heard it I had to recover from the crouching "grenade" position. I actually saw it happen a few months later and there was a little fireball that came out of the blower.

  Hopefully if you guys don't find this informative,  you do find it entertaining.

[Glenn]

No watering or steam involved when my forge backfired.