Hello, I have built a propane forge and when running it for a while the jet changes and starts to stutter.

This is a video of it when I just lit it, it is running well, a little bit to much gas. I will open up the air intakes later on.

http://www.youtube.com/watch?v=hN0UAjuImJc

This is a video when the forge is running badly and I limit the air intake. Then it starts running properly again for a while.

http://www.youtube.com/watch?v=1tgWz0H2zJ4

What do you think is the problem? To much gas and to little air? I am using a 0.8 mm tip right now. Should I use a smaller one?

/E

Do you have a separate expanded nozzle that you can use to adjust your flame? Usually if the nozzle and choke are adjusted properly with the right gas volume you you won't have a stuttering issue.
i assume you have read Ron Reil's forge and burner design pages on the ABANA website? http://ronreil.abana.org/design1.shtml

With more information from you; you may get more thoughts on this: Did you build the burner from plans or just from materials you had? If you built from plans did you follow those proven plans exactly or change anything? i built my own a lot of years ago and used plans. If I converted your metric tip size correctly it is a little smaller than wot worked for me. Chart says a little over .031 I fussed with mine a bit and ended up with a .035,,Lots of folks posting here say they used that size also. And do you have a pressure adjustable regulator in the system? When I turn my pressure down too low it acts just like yours in the second video.

Wot size lpg bottle are you using?,,,not sure where you are but bottles may ice up in use, More so if they are low on fuel.You will see this as a frost line on the side of the bottle at the line where the liquid is turning to gas inside.

Hello, thank you for your comments.
I have read almost everything on that site, but the amount of information is massive. :)

I have built it by combining the information from different types of burners. Not exact plans. The problem is that in Sweden we are metric and not all the different bushings and assemblies are available, so I had to make some changes to the different plans that are available.

This is how the burner looks:




This is the air intake:



And I am running the burner at about 19 PSI, approx 1.2 Bar.

I use a P45 (45 Kilo) propane tank.

I have a adjustable regulator. When I turn up the PSI it does not stop stuttering. It only starts doing this when it is hot enough.

This a movie of it running in free air.

http://www.youtube.com/watch?v=EslQd7DamLg&feature=plcp

I forged the flare, so it is not a scientific 1:12 ratio. But the flare "sticks" properly to the burner even on high PSI.

Thank you for your help.
/E

Very hard to diagnose a problem with a mutt type burner. That is why Rich ask about following a proven design. One feature may work very well with the type burner it was designed for but not work well at all with another. Choose one design and if it's not working, its easier to fix. Also, try one fix at a time. Don't change the air flow volume AND change the orifice size, for example, because if it still doesn't work right, you don't know which issue is giving you problems. In other words, don't try to fix what you're not sure is broken

It looks like you need to adjust for centered down the pipe. Adjusting the position of the nozzle in and out along the length can change your fuel/air mix between lean and rich.

Hooking up to water can make this very obvious if you are misaligned. It is also cold making for easier adjusting for centered. Use a small box wrench or some screwdrivers or needle nose pliers to bend and tweek the aim of the jet.

What pipe diameter are you using 3/4 inch (19 mm)? The .8mm (0.030 inch) tip should be fine if you are. Changing up a tip size is up to you.

Phil

You may have already tried these suggestions, if you have, just ignore them. First put your gas jet a little further down in the burner. It looks like you have the end of the jet just slightly above the end of the last hole. I have mine positioned about 1 cm past the holes. Then loosen the nozzle and while running the the burner pull the nozzle in until the flame dies out. Mark that point. Then running the burner again push the nozzle out until the flame again dies. Mark that point. Now position the nozzle halfway in between the two marked points and tighten it up or fix it to not move at the halfway point. See if that helps.

I've not tried a burner of that design and want to learn a bit about them.

In the bottom video, I assume you restricted the airflow at about 2 seconds, unrestricted it at about 3 seconds and it burnt ok until about 15 seconds?

Did the flame travel back up the burner toward the jet when the noise changed at 15 sec?

I have made several different burner types, all with fairly good success. I would think your version should work OK if you get it tuned properly. .8MM for an orfice is a small size, but should work OK. That is between drill bit sizes 67 and 68. Drill bit size 60, which is a little over 10MM, is a generally recommened size for burners. I have used drill bit sizes from 60 to 70 with success. You can find a table online to tell you the sizes of each numbered drill bit (Google).

I agree with Phil for you to confirm that your orfice is centered down the pipe. If the orfice doesn't squirt the propane down the center, the results will be unsatisfactory. Second, if you can plumb in a good (industrial quality, not the hardware store types) needle valve near the end of the burner, you can control the propane volume, and vary the needle valve position to get the best consistant flame (also, it will be easier than using the regulator to increase or decrease the heat from the burner). Third.... play a little with the position of the flare. If the flare is not in a fairly optimal position, the burner may not behave well. 12 degrees is supposed to optimal (according to someone anyway), but it certainly is not critical.

One last thought.... If you can't get your burner to behave with these (and those from other members) suggestions, cover the set of holes nearest the input end of your burner, you may have too much opening for an optimum mixture with your size orfice. Some burner designs have a sliding cover so the amount of air coming in can be tuned also.

I made a video, describing how to make a burner similar to this (orfice mount slightly different than yours). If you are interested in viewing it, use this link...

http://www.youtube.com/watch?v=VxzdqcPzXj8&feature=channel

Good luck....

Hello all, thanks for your replies.

Dodge, you are correct, it would have been much better to run with a tested design. I built it because a friend in a swedish forum had successfully built one similar and when I saw Daves howto movie I thought it would be safe to build one.

Phil: I centered after that picture was taken, so it was as dead center as possible. I am using 3/4 inch pipe. 0.8 mm nozzle. I had the impression that I needed a smaller tip.. but that may be wrong.

Fatfudd: I have not tried to move the nozzle, I positioned the tip 1 cm over the last hole because the burner that I used for a reference had it there. But it also had one of those sliding chokes that I do not have. So I will change the position as you say and mark the max and min. Do you think it will be dangerous to pull the nozzle out to much? I do not want it to start burning outside the burner... Should I do this test outside the forge or with the burner positioned inside it?

timgunn1962: It is as you say in the video. I restrict the airflow, unrestricted it and the burner burns just fine until 15 sec. I do not think the flame went up into the tube when it started to stutter.

Dave: Nice of you to post here, it was your video that made me go for this design. I have been planning to build a burner for several years, and when I saw both my friends build and your tutorial I thought that I need to start testing and not keep on just planning and reading up on burner designs. The big problem here in Sweden is to get all the proper parts for a burner. The parts are dirt cheap but the access to it is crap. I think I will try to tweak according to your recommendations and then if it does not work, either buy a T-Rex, shorty or a z-burner kit.

I need this small forge to be my "workhorse" when I forge the shape of the blades. I will not do any welding in it. So I may remove the shelf and only use wool for saving heating time.

Thanks again for your help. I will post more test results after I been on vacation for a week.

/E

Melchior
Sorry, to be clear I was referring to moving the flare when I said the nozzle not the jet. Leave the jet fixed slightly past the holes and just move the flare. You should do it outside of the forge so that you can mark the locations when the flame goes out. Also if you can set you pressure at about 6 psi when you are adjusting it will be a more accurate.