i just recently purchased a vulcan firepot. it looks like the opening for the air pipe is 3". the only problem is that i cant find a flange anywhere that big. any ideas where i could find one or how to hook up the air pipe? i currently have a few lengths of 2" pipe and a hand crank blower.

When I was faced with that problem I looked around the hardware stores until I found and floor flange that would cover the diamater of the vulcan fire pot . Then I adapted down and connected to my air source with flexible tubing form Home depot. Some times local plumbers and hardware outlets have stuff that Home depot doen't think to carry.

Probably an unnecessary comment but remember not to use galvanised pipe in any part of a forge that get hot.

lol yeah i'd rather not die of zinc poisoning, but yeah its getting the floor flange to fit the forge that i havent been able to find. im going to try a few plumbers supply stores around here and hope to get lucky.

I see four options:
1. Use a section of metal flex pipe for clothing dryers and jam an end into or over the end of the blower and an end into or over the end of the firepot air intake.
2. Forge a reducing fitting out of 2" pipe. Heat up one end in a forge and expand that end over the horn of an anvil or on the end of a floor mandrel.
3. Cut a 3 inch disc out of steel and then cut a 2" hole in the center.
4. Go to Fastenal.com and purchase a 2" flat washer with "plain finish" (no zinc coating, just oil finish) Product Details | 2" USS Flat Washer plain finish DOMESTIC | Fastenal
and attach the flat washer as a reducer to the firepot.

Your best solution depends on what tools you have available to you. If you are lacking in tools, then the flex pipe from a hardware store and duct tape may be your only option.