Andy98

Thanks - it's funny, I will likely have to transition from worrying about not enough output to dealing with too much. It'll take me a while to accept that concept - but I guess that makes sense given the total BTUH potential I calculated. I went with the ball valve simply because someone else had used one in their NG build - but I did have it mostly closed already, so if I do need to meter it down further I won't have have a lot of precision. I'll look into globe valves. The NG hose is 3/8" and the output pipe is 1/2" - are you suggesting a 1/4" globe valve then?

Hi, thanks for your comments. The fan in question is a beefy unit, actually, not your typical fan by any means. To illustrate, I picked this typical cheapo 40mm fan for comparison. The fan I'm considering is: Almost 3x the depth of a typical fan (2.8cm vs 1cm). That should allow the blades to be more "scoopy", so to speak, which makes sense to me as what you'd need for higher static pressures. It Is 4.5x faster (18000 rpm vs 4000rpm) - which means it's not only bulk moving more air, it means there are higher tip speeds involved. It draws almost 10x the current (0.43A vs 0.05) and thus higher wattages as well (5W vs 0.4) It's almost 3x louder (54dB vs 20) So, assuming the manufacturer isn't outright lying about their fan performance specs, then it should be able to keep up with the draft inducer I tested with. The draft inducer appears to have a lower static pressure max (~1inWC vs almost 2 for the PC fan) but for sure has a much higher CFM in free air (the video shown has the draft inducer running with it's opening gated down to about 10% of max - it makes waaay more air than I need). I'm not sure what else I could be missing here - but of course there could be something. At this point I think I've proven enough things out that it's a reasonable next step, and if it turns out not to work then I'm out less than $40 anyway and can revert back to the draft inducer. Finally, I'd rather take a shot at the PC fan than continue to invest in the draft inducer. To finish the draft inducer approach I still would need to make a weather resistant housing for it, get better ducting, get some proper HVAC reducers, and make a better gate valve. There is at least $20-30 worth of materials required there and probably about 6 hours work. The PC fan, if it works, will give me a clean solution with a lot fewer hassles. It'll be easier to setup, store, etc....plus I'll be able to modulate the speed better. ..and I'll have fun building the PWM circuit.

Hi, 1) Control probably would be better - but I doubt it's necessary. It's regulated (at the gas main) which is all of 40ft away, so I suspect my pressure will be pretty constant (there isn't a tank that will deplete or change temperature). Also, I think an adjustable regulator for such a low pressure range would be hard to source. 2) The funnels were a (largely unsuccessful) water toy for my kids. They pour water into them, or use the hose. Seemed like it should be fun, but in reality they just like to use the hose and don't seem to care what, exactly, they are filling/soaking. Cheers, Andy

Due to unseasonably warm weather, I was able to find 15 minutes today to give this burner a test run: It definitely seems to work. This video was take about 20 seconds after it was lit for the first time. I didn't spend much/any effort trying to tune it. The NG valve is not very open (it's a ball valve, turned maybe 20 degrees (with 90 degrees of total travel). My observations: It's odd to me that I do not see an actual flame cone. It seems to have gotten a lot of the forge wall to an orange heat faster than my propane burner. There seems to be a cool spot where the gas is hitting the sidewall, rather than a hot spot. I guess that means the gas isn't actually burning when it hits that wall, but I don't understand why the ceiling of the forge is hot along that same line. I believe some of the behavior will change when the forge is actually fully hot. I'd love to hear other's observations. I take this as a pretty positive test. Based on this, I'm thinking of buying one of the CPU fans (this one) so I can get rid of the draft inducer. Thoughts and comments are very welcome.

Different thicknesses. Ive been told, but I'm not sure its true, that the white tape is not any guaranteed thickness and is used in unregulated applications. in any case, you don't want the tape to apply the tape to any joint that will get hot. So use it for the gas supply feed, but not the burner itself.

Ok, so more info (forgive me, I'm using this as a multiplatform notepad to some extent): I've built the burner very simply: 3/4" black pipe T 3/4" x 6" black pipe nipple as mixer tube NG goes in drop/bottom of the T (3/4 to 1/2" bushing, 1/2" x 2" nipple, 1/2" to 3/8" flare full port ball valve) Air goes in the run of the T (3/4 x close nipple, 3/4 to 1.5" PVC bushing, 1.5"x2" PVC reducer) Basically, the most controversial thing above is that I've decided to just try going 3/4" for the whole assembly rather than using a larger diameter and reducing it as a nozzle (e.g.,going from a 1" or 2" down to a 3/4" nozzle). I did look into the flow-resistance of 1" to 3/4" black-pipe reducer, and the few bits of reference material I could find implied that the reducer itself was equivalent to around 10-20x the downstream diameter (10x3/4"=7.5") which means the reducer looked like it was going to add more back pressure than just having the whole short length at 3/4". So I decided I'd give it a try. Cheap parts, why not. I've also chosen a relatively short mixing tube (at 6"). This follows the T-burner guidance of 8D, plus I figure there'll be enough turbulence in the T to mix it well (who knows?). I put it all together and gave an airflow test with my draft inducer. Using my highly calibrated plastic garbage bag, I appear to be getting around16cfm. Still above my target. I did a crude pressure drop measurement using my plastic tube manometer, and it looks like I'm like my 3/4" pipe arrangement creates >0.25inH20 of pressure head. Seems ok. Interestingly, I am measuring almost no pressure drop between the fan outlet and the inside of the T. Again, these are really crude measurements. In contemplating how to get the blower hooked up to the burner, I started looking into some axial fans (like regular PC fans) rather than blowers. The benefit being that I could simply stick one of these into the 2" PVC reducer, rather than having to duct it in. It also means I have less weight to support, and the burner assembly becomes more portable. That turns out to be a goldmine - still using the 7cfm desired flow to make this list comparable to the one from my previous post: 7cfm @ 1.1inH20, $16 (NMB: 1611RL-04W-B80-B00) 7cfm @ 0.8inH20, $14.58 (Mechatronics Fan Group: MD4028V12B-RSR) 7cfm @ 0.6inH20, $17 (NMB: 04028DA-12Q-AA-F0) 7cfm @ 0.7inH20, $19 (Sunon: PF38281B2-000U-A99) 7cfm @ 0.8inH20, $19(NMB: 04028DA-12R-AU-F0) Since I don't trust my pressure measurements, I'd probably look at the first one.

I've been using this conversation over on reddit as a rough guide for my planning. I've decided to do a lot differently, mind you, since I want to try and make the whole burner assembly smaller.

...I've always been confused on whether excess flow valves are actually on the tanks. Are they on all tanks? Or only larger tanks? I read one thing that suggested only motor-home tanks had them, but that for BBQ tanks at least it was always in the pigtail. I've had a hard time finding clear answers on this...

Question for clarity: You're saying that once the tank is half-full, the tank-side gauge reads zero and the burner produces no/little flame and it stays that way until you fill the tank up again - so even if you shut it all down and came back a week later (with the tank above freezing temperature) the tank would still not work, and would still read zero pressure? Also: The regulator is connected directly to the tank valve (no other hoses, etc..)? What kind of connector (POL connector?) Are you sure your regulator(s) don't have excess flow protection? Some of the regulators designed for fryers/boilers have a excess flow protection mechanism built into them. The reset on those is to shutoff the propane at the tank, disconnect the valves, the put it all together again. Here is a good explanation: http://www.rvdoctor.com/2001/04/not-your-fathers-pigtail.html

...yet my stove and my BBQ apparently are managing to push enough gas and air down their burner assemblies - so it's obviously possible to some extent. I've resisted bringing my furnace into the discussion, since it has a dedicated draft inducer, but older lower efficient furnaces did not - using nothing more than the residential NG gas pressure they were more than capable of producing a small forge worth of heat. I speculate it's about size - even a small furnace has multiple large burners.

Thanks everyone. So, if a Natural gas stove and grill can run NA, inducing enough air for combustion, then what stops a NG forge burner from doing the same? The only guess I have left is that there would be a max orifice size (and thus max burner output) that can work at NG residential pressure...?

I'll be interested to find out how they do. They look to me to be the glass filled nylon wheels from Oregon Knife Maker (I stumbled upon then from here: http://dcknives.blogspot.ca/2016/11/2x72-grinder-wheel-set.html). For some reason his wheel sets (metal and plastic) have two crowned wheels...I always thought you only wanted one... @RogueGeek How are you finding it rigidity wise? The all steel 2x72s always look crazy overbuilt to me, but I've never used one so wouldn't know for sure.

Really nice! Was it just 1018-W2-1018? In ine of the photos there is a neat crystal effect around the shinogi? The photos are something else too!

Frosty, a question on that front: I've been assuming that gas stoves and grills must not be inducing any/all/most of their combustion air (my stove doesnt look like it induces any...) mostly because of their low pressure operation. I was guessing they would just combust with the free air at the flame point. Is that right?

Ok, some measurements now: 1) The draft inducer (not the computer fan): I measured it, using a makeshift poly tube manometer, at 1"WC when full blocked. 2) When connected to approx 5' of 4" flexible plastic duct line, which will not be the final install, it was able to move approx 26cfm of air. 3) With my NG connection, the 10' 3/8" BBQ hose with nothing connected to it will expel approx 6.3 cfm of natural gas. That's 378 cuft/hr, and if I assume 1000 BTU/cuft then that's should be 378,000 BTU. So with a target of approx 40000 BTUs, and thus a need for 0.6cfm of NG and 6 cfm of air, I seem to have a 4.5x margin on the air supply and a 9.45x margin on the gas side. So I feel like this has a pretty good chance of working. Also, even running full out at 378k btu, I'd only be burning $1/hr of NG.

I do my forging in my extremely small, big-city back yard. To get the 1" line back there I'd need/want a gas fitter to do it and there would need to be an external wall penetration and I'm not quite ready to make that kind of an investment yet. Perversely, the more serious I get about this hobby, the more likely it is that I'll end up relocating where I forge (i.e., not in the backyard at all). I could also get shut down by an annoyed neighbor pretty easily, based on the local bylaws (as I read them at least). I'm prepared to have to tinker, and I'm also prepared for this to fail - although I will be disappointed. I figure that I need less than $20 worth of black pipe and fittings to get a test run going (using the BBQ hose that is actually connected to my grill). If that works, then I'm happy to invest more. If it doesn't work then I ruminate and possibly go back to propane. I am putting a lot of energy into resisting the temptation to just experiment on burners instead of actually forging. On that topic, I'm at a loss as to how I can actually measure the effectiveness of my burner? Other than "will it weld" what kinds of tests can/should I do?

Hi - Sorry if it seemed I was trying to offload work. That wasn't my intention - I am just looking for additional "gut checks" on NG supply being sufficient. As you are no doubt aware, for every "I built a NG Forge" post out there on the internet, there are 100 posts stating that residential NG can't work. I'm sensitive about the NG supply since I know my feed is not ideal (being at the end of a 3/8" BBQ line...). Thanks as always for your comments! I'm hoping I can get some of this build done during the winter months here, but I will post further once progress is made however long that takes...

Ok, so I'm now starting to process what you said here and it leads me to few questions: Are there any design guidelines for the mixing tube? I am aware of the guidance for naturally aspirated burners, but I don't know if they apply to forced air, and to forced air with natural gas in particular. How would I diagnose inadequate pre-combustion mixing? Regarding the outlet: I'm not prepared to make a ribbon burner (I don't think my small forge would accommodate it, but mostly I am looking to avoid buying a bag of refractory). I can easily do the 1" to 3/4" transition. Should I consider making a small manifold and having 2 or 3 small (1/2") burners? I'm inclined at the moment to try and keep it simple (ok, I'm inclined to overthink and overbuild it, but I'm disciplined enough to keep it simple...) What is a good design flame speed to shoot for? I know people usually say 1ft/sec for NG, but from here I see that at high temperatures it can get to ~ft/sec. At 2ft/min even 1" pipe at (say) at low end operation of 2cfm should keep me above the flame speed...? Also, I went and checked out the eclipse engineering guide you posted a while back. Using (abusing) the orifice table, it tells me that a 3/8" orifice at 1"wc will yield 270cfh (4.5cfm). If I pretend that is comparable to my 10' long 3/8" BBQ hose with closer to 7"wc NG (yes, lots of approximation) it suggests a fuel BTU potential of 240,000 BTU. I have trouble accepting this number (and have no practical experience to validate it) but it's encouraging!

Understood. See below the next quote. Great link! Their products are competitive - randomly picking a blower model #PMB1297PYB1-AY it looks like they are around the same prices ($30-40) as the other fan I mentioned above. At 7cfm, it'll handle .8inH20 which means it'll work for 3/4" and 1" but not 1/2". The fan I mention above would only work at 1" pipe sizes. Regarding the fan curves: If I look at the ones provided by that Sunon link, it looks like (for their fans at least) you can almost just treat them as linear and then round down a bit. So with the .27inH20 and 100cfm fan I mentioned in my previous post, it seems somewhat likely at .08inH20 it'll do something a little under 30cfm, well above the 7cfm I need. So - apparently there are options! Actually digikey is fantastic - makes sense that they have full spec sheets. Some other options: 7cfm at 1.1 inH20, for $28. 7cfm at .7 inH20 for $25 7cfm at 3.7 inH20 for $45 ...seems like lots of choices from our friends in the electronics industry. That last one might actually work with a 1/2" burner. Downside of these blowers is that they are not variable speed as far as I can tell, so they'll need gates.

Hi - thank you very much for your reply. Lots of stuff in there to address (plus I have a week of additional calculations and research done). I arrived at the BTUH using the BTU calculator referenced off Ron Reil's site - it's working off orifice size and input PSI to calculate BTUH. The same spreadsheet also estimates propane consumption in hours, and that seemed to line up approximately enough with my real world results. I then proceeded to round up to help ensure that I had the necessary headroom. No doubt I did. I was working with a really first-principles calculator scrounging all around the net for input values. I found a better calculator, intended for HVAC (here: http://bry-air.com/resources/utilities/static-pressure-calculator/) that gives me results closer to yours. I'm now calculating that 2' of duct carrying 7 cfm (I've upped my volume a bit) will present: .08 inH20 (1.98 mmH20) @1" nominal. .28 inH20 (7 mmH20) @ 3/4" nominal. 1.22 inH20 (31 mmH20) @ 1/2" nominal. ...plus, as you indicate, additional static pressure amounts for bends, constrictions, etc. The mm units are there because that's how computer fans are rated. More below... Yes - so what I've uncovered is that there are (now) two classes of computer fans being sold - some optimized for high volume/low-pressure, and others optimized for static pressure. Unsurprisingly, the high static pressure fans are called "Static Pressure Fans" and the highest rated one I could find in 120mm size has a static pressure rating of 7mmH20 (0.27inH20) and 100cfm. This a $35 fan, not the $8 fan. Bonus is that it's IP67 rated. I found one that went to 10mm in 140mm size. Both are PWM variable speed, and 12VDC. The manufacturer for these fans is here: http://noctua.at/en/products/fan So it looks like right off the bat I'd need to go to 1" for sure, but it seems at 1" it might actually work - by those numbers at least. Next thing I looked into was the NG supply. My NG supply piping would look like this: Gas Company Regulator -=> 1" black pipe, approx 30' + 6 elbows and 2 T's -=> Reducer to 5' of 1/2" copper -=> 3/8" quick connect -=> 10' 3/8 flexible BBQ hose -=> Burner. Unfortunately, I haven't found a good reference for calculating the NG flow. If I approximate by pretending that the 5' of 1/2" copper + 3/8" quick connect + 10' of 3/8" BBQ hose is equal to 15' of .3" ID duct, then that same calculator tells me I'll drop 2inH20 (0.07psi). That seems suspiciously low to me. Any thoughts on this calculation? I imagine that there will actually be some amount of suction on the NG outlet inside the burner as well, which should a bit? ...actually I am talking about one of those cheap, inline paddle wheel draft inducers. It was free, so I'm not out anything - will it not be up to the task? Thanks again for all information and the time taken to respond. I'm not 100% convinced I'll proceed with this yet, by the way. The biggest obstacle is that I'm cheap, and the 10' NG hose ain't. At full price for that hose alone, I'm looking at a 2-3 year payback with the meager amount of forge time I get. If I do proceed, I will certainly update with results.

Wow - I see now they do carry cfm ratings, but no performance curves. Any suggestions on how much I should derate their cfm? I'm looking at a 70cfm 120mm fan with pwm speed control, for all of $8. That seems...too easy. I suppose (wonder) if I needed to I could stack them like tubine stages...

I didn't realize that they would work! I think I saw you mention them in the burner thread, but I thought that was just to induce a swirl. I assumed they must not get enough flow, and that for sure they weren't build to deal with any kind of back pressure. Is sizing just a trial and error kind of thing? I dont believe I've ever seen a performance rating - just a physical size rating.

One can be negative and critical: "This place is stupid, and we do crap work" And one can be positive and critical: "We are not doing the best we can. We are capable of doing better" Negative is demoralizing and corrosive - it does wreck a workplace. Meanwhile positive and critical people can compeletly transform a workplace (if allowed). It's cynic/critic vs coach. Coaches are great. Maybe talk with your manager, tell him you really want to help improve things, and ask him for advice on how to do it. Be open to what he says. Also ask him for help - two people are better than one. Or maybe your workplace is pathalogical... I read a study once that compared actual error rates of people in various roles, to perceived error rates of those people. They found that weathermen had the best handle on how correctly they do their job, since are errors are quickly apparent and irrefutable. I think about this at election times whenever an incumbant government gets the boot. So here in Canada we pushed out an old incumbant government about a year ago. For that to happen, millions of people must have had to decide that the guy they voted for 4 years ago is no longer any good. Its an opportunity to go look at your decision 4 years ago and ask, "Did I get it right?" and if the answer is "no" then start asking why you blew the call.

Hi, I'm in the contemplation stage of a forced air natural gas burner. Typically when I see forced air burners (and NG ones) people use 2-3" pipe. I believe most people do that using the argument that you need a higher volume of flow, and thus larger pipe. I'm getting stuck on that line of reasoning. Here is my logical argument: I am essentially trying to replace my 1/2" T burner with a NG forced air burner. Lets assume that my T burner is producing 30000 BTUs (just to anchor the math - I believe that is almost the top end of where I operate it). 30K BTUs = 11.6 cuft/hr of propane, and will need 24:1 air:fuel by volume for a stoichiometric burn. That means a total of 290 cuft of gas/hr for my T burner. 30K BTUS = 28 cu/t/hr of NG, and will need 9.7:1 air:fuel by volume for a stoichimetric burn. That means a total of 299 cuft of gas/hr for my theoretical NG burner. I know that the gas/fuel mixture inside my T burner *must be* atmospheric, or slightly below atmospheric - so it's not like it's "packing in" the volume and benefiting from that. I need a blower volume than 300 cuft/hr or 5 cuft/min. I'm cheating and assuming that the blower is pushing all of this (even though only the air is going through the blower - the NG is being injected afterwards and thus contributes probably to some backpressure on the blower....) I understand and accept that the larger pipe will have lower flow resistance. The blower I am planning to use is a furnace draft inducer. I don't have a spec sheet for it, unfortunately, but it seems to move a heck of a lot of air - I find it hard to believe that it couldn't push 5 CFM through 1/2" pipe, or even 1" pipe if necessary. If I do a bunch of hacky math using sketchy online calculators, then I calculate that 3ft of 1/2" black pipe will give me less than .3in-h20 of static pressure loss at these velocities, and inferring from other blower data that might bring the 100cfm down to maybe 50cfm, still well above the 5cfm I'll need. That diverges a lot from the 2" and 2.5" pipes I see people using, so I'm of course worried I have lots of things wrong. Does anyone have any comment or suggestion here? Where and what am I missing? Has anyone made/used a small diameter pipe blown burner? Thanks!

Fantastic post. Thank you very much.