Awalker

I see what you are saying about the blown burners, and no I havn't see many well designed homemade ones. I was assuming the blown and venturi burners to have the same size orifice. If the orifices are different sizes then no, pressure is no basis for comparison. So, assuming that, PSI has everything to do with fuel economy, as the higher the pressure the more gas can be crammed through the orifice until such a point as the orifice goes sonic and no more gas will go through no matter the pressure. BTW, my burners are venturi burners that I am forcing air into, when the air stops on mine they still run just fine. When I am running my burners (with #65 orifices) at 7psi they are more economical than running them at 12psi (uses less fuel at lower pressure), but I like the hotter forge running at the higher pressure. So if I add the forced air I get the hotter forge at a lower pressure. The thing I am curious about is the other pipe forge I used had #72 orifices, and would run all day long on 4 gallons of LP but I can't get mine to run on #72 orifices.

Looper, I have worked in the gas industry for 15years and PSI means as much as orifice size. For each orifice size you will get a certain amount of btus per pound of pressure. So if I wanted to get a certain amount of btus I could use a small orifice size and higher pressure or a larger orifice size and lower pressure. There is a chart around here somewhere with the btu rating and pressures of various orifices. Volume (your flow rate), and pressure are inversley related to one another as per the ideal gas laws, so pressure does mean something! The main reason I see people putting 1/8" or 1/16" orifices in blown burners is that the burners are adjustable by installing either a needle valve upstream or adjusting the pressure regulator upstream to change the flow rate of the burner for their desired characteristics. I have also heard more variable fuel usage reports from people with blown burners for that very reason, they just have them adjusted to use too much fuel. A well designed forced air burner won't explode with the forced air stops either. Now if you are running to rich and you stop of the air supply the flame will want to exit the forge looking for air to burn but it won't explode because it is already on fire. Also, just a point to ponder, how many people have changed to blown forges, then gone back to atmospheric?

I would be very interested to see some pictures of both of your pipe bells. I have made some cylinder bells in the past but quit doing them when they got to be so ubiquitous.

I really like the forced air, and the compressor solution is temporary as I didn't have a blower around to try.

I just changed my forge from a single burner at an angle in the side to a two burner from the top. The side burner was a Ron Reil 2 x 3/4" bell reducer burner. When I changed to top burners I used a 1 1/2" x 3/4" swage into a 3/4" elbow then into a 4 1/2" nipple and I used a forged 3/4" coupler that I flared the end on. I started out with a #72 drill size orifice but found it to be unstable and wouldn't stay lit. I bored it out to a #65 and it is much more stable but still not as hot as I'd like I am running it around 7 to 12psi. I started out with the #72 orifice as that was what was in a forge I had used previously that ran fine, and would run all day on about 4 gallons of LP. My single burner would use every bit of a a 5 gallon tank in 5 hours (it had a #56 orifice in it running at 17psi). I think I may go back and rebuild the venturi portion of the burner with the 2x3/4 bell reducer, as that seemed to work well on my other burner (I didn't have 2 of them handy or I would have used them on these burners). After I had it running I played around with injecting some air into it to see if it would burn noticably hotter, and it did. So, I made an additional air injection manifold that stands off the burner a few inches and has a valve I can throttle that is connected to my compressor. It doesn't take a lot of 175# compressed air to make a big difference in the flame characteristics and I was very impressed. I think when I change the swages out I am going to change to a blower as well, the compressor works but adds even more noise and a 7.5 horse motor coming on and off all the time is annoying. With the air injection on I can run the LP pressure around 3 to 7 psi and it gets good and hot in the. BTW the forge is made of 12" pipe that is 12" long. I added Kaowool when I moved the burners and that made a big difference (it had a firebrick liner before), and it has a brick closure in front and back. Any thoughts on those burners would be much appreciated.

I am making some larger scrolls on the scroll jigs I made.The scrolls are 8"-12" in diameter and porbobly use 24"-36" of stock. I have used the jigs quite a bit for smaller scrolls and had no trouble. I notice that when I take a nice long heat, to get as much of the scroll formed as possible that the square bar (1/2") wants to twist. This only seems to happen when the stock I a scrolling is long (6') as the shorter ones seem to come out without the twist. I am wondering if I am taking too long a heat and my right hand bias is coming out, but the shorter heats it is not apparent. Any ideas on this would be great as I have about a dozen more of this size to make.

Manual pressure control or regulated? If it is a manual control use 1/16th inch holes, if it is regulated you need to know the water coulumn pressure you are running at and the desired BTU output to arrive at the orifice sizes.