forgemaster Posted June 1, 2009 Share Posted June 1, 2009 I have been given a gas furnace in pretty good condition from our local TAFE college. It has a blower installed on it and was set to run on natural piped gas. We normally run our big furnaces on oil but we do have a bulk LPG tank for running our little furnace that we use on our 2cwt hammer. The little furnace is a venturi style 2 burner setup using fairly high pressure LPG. My question is has anyone had any experience in conversion of natural to LPG, ie will I have to change jets, mixers, and recomended or suggested gas pressures to use. Basically I was going to put a plug and cord on the blower, plug it in, connect the LPG to the furnace, put in a lighting flare and see if it will light. I can reduce to LPG to what ever pressure is needed. The furnace internal dimensions are about 12" wide x 18" long x about 10" high. The burner comes in from the top of the combustion space. Ta Phil Quote Link to comment Share on other sites More sharing options...
AndrewOC Posted June 1, 2009 Share Posted June 1, 2009 Hi Phil, for a memory jet needs to be smaller for LPG than natural gas, LPG has more oomph. Examples are buried somewhere in anvilfire site... (burly) Andrew oc Quote Link to comment Share on other sites More sharing options...
jimmy seale Posted June 1, 2009 Share Posted June 1, 2009 if memory surves me. nat gas carries more O2 than prop. naturaly so jets need to be smaller, and O2 needs to be increased.but a ratio i sure don't know so i guess experiment but be safe about it. Quote Link to comment Share on other sites More sharing options...
ThomasPowers Posted June 1, 2009 Share Posted June 1, 2009 No need to "experiment" a good gas supply place should know how much to reduce jet size to go from NG to Propane. For a simple burner they did it for me by soldering over the jet and redrilling to the proper size. If you don't have to guess you don't have to worry about guessing wrong! Quote Link to comment Share on other sites More sharing options...
Nakedanvil - Grant Sarver Posted June 1, 2009 Share Posted June 1, 2009 Forgemaster: Kind depends on how sophisticated the controls are. Some sensors and solenoid valves won't work on higher pressure. Easiest thing is to get a regulator from the gas supply and install it on the forge. If it has a blower there probably isn't any sort of "jets". Probably has gas and air controls so you shouldn't have any problem. Quote Link to comment Share on other sites More sharing options...
Charlotte Posted June 1, 2009 Share Posted June 1, 2009 Forgemaster: Kind depends on how sophisticated the controls are. Some sensors and solenoid valves won't work on higher pressure. Easiest thing is to get a regulator from the gas supply and install it on the forge. If it has a blower there probably isn't any sort of "jets". Probably has gas and air controls so you shouldn't have any problem. If it is a fixed forge, which we can assume it is, then there may be local fire and safety regulations that have to be followed. Some localities require inspection of every change to installed systems. Quote Link to comment Share on other sites More sharing options...
Frosty Posted June 1, 2009 Share Posted June 1, 2009 Talk to the manufacturer, they'll have the LP conversion "kit" and instructions to do it properly. Check with the fire marshal, insurance, etc. to make sure you're covered. Here, most insurance companies will NOT cover a gas appliance that's been modified by the owner rather than the manufacturer or authorized agent. Some places here do not allow ANY modification of a gas appliance other than lp/ng conversion. Frosty Quote Link to comment Share on other sites More sharing options...
Nakedanvil - Grant Sarver Posted June 1, 2009 Share Posted June 1, 2009 Charlotte & Frosty: What a bunch of wimps! Actually you do make good points, I just kinda tend to to what works. In an industrial forge there is usually no such inspections. Most inspectors are lost if it's not a range, furnace or hot water heater. If it's a commercial for made for low pressure NG then a regulator should do just fine. Quote Link to comment Share on other sites More sharing options...
forgemaster Posted June 1, 2009 Author Share Posted June 1, 2009 No Brand on it probly made in bulk to supply the tech colleges all around the state, all had pretty much the same thing. Asked gas supply people, they looked and said,"wow thats a really big furnace, we don't know. Heres a bloke you should ring." Rang the bloke, same reaction. Nakedanvil you're correct, I don't see any "jets" as such. It is all manual control. Adjustment on the air, adjustment on the gas. Have no fear all, I have a current copy of the relevant Australian Standard for fired furnaces and heating apparatus. It will all be done to Standards. Thanks for the help guys Phil Quote Link to comment Share on other sites More sharing options...
forgemaster Posted June 9, 2009 Author Share Posted June 9, 2009 Thanks guys for all your assistance. Flashed the furnace up this arvo on LPG, just put a 3 phase plug on the blower to see if it would run. It was a goer, so connected up the gas and put in the flare, we had to set the pressure regulator back to about 5 psi to get the furnace to run with all valves full open. It ran up to about 1200 deg C in about 1 hour which is about what I expected for a furnace of that size that has sat outside for 3 or 4 years in the weather. It lit up OK with very little mucking about then I tweaked some of the settings as suggested by Nakedanvil to get a efficient combustion. Will give it a whirl with a couple of real jobs tomorrow, and take some photos as well if I can remember. Very happy forgemaster tonight Thanks everyone Phil Quote Link to comment Share on other sites More sharing options...
arftist Posted June 9, 2009 Share Posted June 9, 2009 Actuly some blown forges do have jets. When I converted my Johnson #122 to propane, I called Johnson, and they told me what size to change it to. What I did was drill the old orifice out to 1/8" pipe tap size, tapped it, drilled my propane orifice size in a brass pipe plug, etc. If I want to go back to natural, I buy another brass pipe plug. Forgemaster, you may want to dig a little deeper. Quote Link to comment Share on other sites More sharing options...
Nakedanvil - Grant Sarver Posted June 9, 2009 Share Posted June 9, 2009 They put a small orifice in for propane due to the (often) higher pressure. So you only have to change it if it came from the factory with the smaller orifice. The big orifice will allow too much gas if the valve is opened too far, that's all. Quote Link to comment Share on other sites More sharing options...
Frosty Posted June 9, 2009 Share Posted June 9, 2009 Whether or not you need to change the orifice will depend on the appliance. Some like Johnson appliances will require it, others will allow you to simply adjust the gas supply. Frosty Quote Link to comment Share on other sites More sharing options...
Nakedanvil - Grant Sarver Posted June 9, 2009 Share Posted June 9, 2009 There's what you should and then there's what you can get away with. When I converted Johnson forges from NG the only problem I had was with the solenoid valve because it was not made for the higher pressure and would not open. So I had to turn the forge on before I opened the service valve. Could have just put a regulator on it I guess. Quote Link to comment Share on other sites More sharing options...
arftist Posted June 10, 2009 Share Posted June 10, 2009 Interesting. Knock on wood, I have yet to have a problem with the solenoid valve. Maybe because I use a regulator? Quote Link to comment Share on other sites More sharing options...
forgemaster Posted June 10, 2009 Author Share Posted June 10, 2009 No solenoid valves, no flame failure device, and after taking it apart no jets of any sort. The gas pipe comes directly into a mixing valve which is adjustable. We have adjusted the gas pressure to allow the furnace to run with full blower flow and the gas tap fully on. Goes like a charm. Only problem now is the workshop sounds like there is a jet engine in here, the oil furnace just has a low rumbling roar, this has like a higher whining sound, along with a roar. Tafe Colleges all over NSW used to have these furnaces and not all tafes would have had natural gas piped in. (As not all towns in NSW have town gas supply) so it is logical to assume that they were made to accept both types of gas. The furnaces were used by metal fab students to heat a disk of plate to hot press a dished end for a pressure vessel exercise which they then had to fabricate. Tafe management obviously decided that this exercise was not of any use to industry so the presses have all gone as have the furnaces. Thanks for everyone help on this. Phil Quote Link to comment Share on other sites More sharing options...
texasroseforge Posted May 11, 2022 Share Posted May 11, 2022 Have a Johnson 120 forge that I picked up at auction. It was set up for NG, but needed to run on propane. Called Johnson and ordered/installed the smaller orifice. Installed a 11.0 LPG regulator. The safety solenoid valve was bad, so replaced it with a “mechanical” back flow valve, it’s working fine. Run off of a 5 gal. propane tank. The forge will light, but as soon as the forced air fan hits it, even at its lowest setting, blows out the flame. Son has lit it a couple times, kinda blew up/popped. Do we put a restriction on the air blower, or did we get something else wrong? I found a replacement for the ITT safety valve, but haven’t put that on yet, but it’s real intention is to open the valve at just the right moment to ignite the gas/air mixture. My biggest concern is that he won’t be able to adjust the air/fuel mixture accordingly, or that he’ll blow his head off trying! Any suggestions/tips/etc... would be greatly appreciated. Thanks, Ross Quote Link to comment Share on other sites More sharing options...
Frosty Posted May 11, 2022 Share Posted May 11, 2022 Ask Johnson gas Appliance, they fully support all their products. But till you do. Is it the stock blower? Do you have the intake gate fully open? I have a 122 I've never hooked up, I have zero use for a huge propane trench forge but when I enquired they sent me a complete, operator, repair, manuals and part book with order forms. They offered every darned THING including paint. Give them a call. Frosty The Lucky. Quote Link to comment Share on other sites More sharing options...
Mikey98118 Posted May 11, 2022 Share Posted May 11, 2022 On 6/1/2009 at 9:17 AM, jimmy seale said: if memory surves me. nat gas carries more O2 than prop. naturaly so jets need to be smaller, and O2 needs to be increased.but a ratio i sure don't know so i guess experiment but be safe about it. You are correct that natural gas (methane) requires less oxygen to burn, but since it also has about one-third less heat output, the fan speed probably won't change much. Various natural gas promoters used to publish gas orifce diameter changes. I think that anyone who sells "gas jets" would have those figures handy. Perhaps some appliance stores... Quote Link to comment Share on other sites More sharing options...
Irondragon Forge ClayWorks Posted May 11, 2022 Share Posted May 11, 2022 Welcome from the Ozark mountains. I'm by far no expert in Johnson gas forges. That being said an 11 WC LPG propane regulator seems to be too low for a forge. Did Johnson recommend that regulator which is usually used for household appliances, BBQ grills, camp stoves etc . Most forges I have seen use an adjustable regulator from 0-20 or 30 psi. An 11 WC regulator delivers less than 1 psi. OK after a little Googling it appears the 11 WC LPG regulator is correct. Do you have the manual for it? If you don't have a manual it is a free download from Johnson. 122 furnace - manual temperature control & thermocouple Quote Link to comment Share on other sites More sharing options...
Frosty Posted May 11, 2022 Share Posted May 11, 2022 There is NO need to figure any of this out yourself, just buy the correct parts for THE one you own. Contact Johnson Gas Appliance. I've PMed the link so it doesn't get deleted on the open forum. Frosty The Lucky. Quote Link to comment Share on other sites More sharing options...
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