When I first set it up, I ran some tests for temp checks, additional paint cure, etc. Basically I treated it like a brand new, unproven device that could have the potential to be a source of serious threat to life or damage to property. My former work background has given me the skills to perform these types of functions with reasonable care and due caution. Watching every possible threat of failure like a hawk is crutial to not having a catastrophic event. Finding the little glitches before they become big problems is one key to success. And last, but definately not least, keep all bystanders away...point being this: what is a safe distance? That's why we do testing, to find out (1) if in fact it is safe, (2) can it be operated effectively (3) will it do what we want it to do?
Caution: this LPG conversion was done to an otherwise un-modified SNP. I strongly suggest that you take any modifcations into consideration if you are planning to do this to your rig. Most note-worthy mods would include (but not be limited to) sealed seams between the firebox and cooking chamber, sealed side door on side fire box, sealed top door on side fire box, sealed cook chamber door, lowered exhaust stack or any other mods which might effect combustion gas venting or flow by means of re-directing, stoppage, regulating, etc. Please, use caution and think it through very carefully before making the changes.
So let's go through the process here.
During start-up and test firing all went better than even I had expected. I always plan for the worst & hope for the best, but I don't expect the latter of the two, especially when "playing with fire". I ran with wide open combustion air intake on side box and exhaust stack vent as well, so it had the best chance of a good draft to keep the flame lit and allow enough venting of gases.
I installed a long-stem cooker thermometer of 50-550 degree range accross the center plane of the cook chamber inlet from the side box. This was achieved by drilling a hole in the cook chamber up front on the left side, just below the door opening and about 3/4" from the left end. I fired the box at temps of 350 for a half hour, then 450 for another half hour. Final cure and test temp was 525 for an hour while watching the flame closely during the entire test firing for signs of impending flame-out situations. The only time I got concerned was with the wind direction changing a few times. It made that funky rumbling sound in the fire box as if she was telling me to get the gas cranked back a bit. Also, I did a few runs of less than a 1/2 minute at wide open flame, and it was a bit more than the smoker could vent out, but, it was also good to know it didn't cause an immediate flame out (or worse).
I did need to re-adjust the air inlet on the venturi of the burner, because the inlet is not in open air now like it was when mounted in the outdoor cooker stand, so it needed to be open a bit more to compensate for some inlet restriction. I knew this would more than likely be the case, but wanted to see how much it would need to be opened-up to dial her in before I touched it, because this was a major change from the designed application. I didn't want to over tweak it and have a nice big bomb in the fire box when I first tried to light her up. No problem there. Just ran low flow, just enough to get a flame, then took it from there to the near full flow for short periods just to make sure the thermodynamics and smoker internal flow characteristics would allow for sufficient expansion and exhausting of the combustion gases. Simple, right? Well for me anyway, I have that kind of thinking.
Pre-testing also included cook chamber temp monitoring with several internal oven type therms and a few external probe thermometers, as well. I didn't want to smoke (burn up) my new rig. Cooking grates and everything that would be in her (except food) during a smoke was installed. Testing cook chamber temps where running very high for a smoker (for me anyway) between 300 to 350 (higher towards the end of the test) and I wasn't getting western with the burner yet, so I kept the flame to a dull roar. Also, I had to consider internal mods to the cook chamber to get more even temps.
During testing, I had the cook chamber charcoal grate and ash pan installed in the normal fashion and at the highest position. That seemed OK for the first modded smoke, but for the Jerky I just did yeserday, I tried something new: I drilled two 1/4" holes in both ends of the cook chamber ash pan to hook the suspension bracket from the coal grate into the pan. Only thing is, I wanted it to hang upside down for this low temp smoke to help disperse the heat more evenly. And it worked pretty well, but during testing this mod it worked opposite of what I thought: The right end had to be lower than the left (fire box) end in order to even out the heat from left to right.
OK, now, this is so weird. I didn't sit myself down yet to really try to figure this one out yet, and I really do like to understand everything I work with. Life seems to be better when you know what to expect under as many possible concievable situations as mother nature or(?) can throw at you. This situation is just too strange for me to overlook or ignore and just shrug it off. Putting more heat closer to the source to get less at the outlet end to even it out...well, it must have something to do with the internal flow of the smoker's gases to the vent stack. Just a theory I'm working on here...like, maybe, if the gases are flowing relatively quickly through the chamber, then, maybe, not as much thermal energy is transferred from the gases to the metal of the smoker's internals and shell. The left end may have a slightly accelerated gas flow in comparison to the mid and right sections, and, this may be caused from the gases still being in an expansion phase as they exit the fire box. Anyone have thought's on this one? Feel free to share.
I also had (and still always use) a vent stack gas temp thermometer to really get a good picture of what's happening in there when smokin' up my grub. Stack temps always run higher on this rig than the cabinet/shell and also higher than the internal rack temps. Usually it's about 40-45 degrees. Normal? Probably, my GOSM does the same thing. I can detect temp swings much faster with this method, than just with a rack probe or two.
I ran it at 450 sidebox outlet temp (with a long cooker probe thermometer) installed at the inlet to the cooking chamber while doing brisket and spares. This smoke was before I lowered the LPG burner to the bottom of the side box. I think what may have been happening there was this: high rates of evaporated water was cooling the smoker gases enough to reduce the efficiency of the burner dramatically. Evaporated water cooling the smoker gases? Yes. Here's an example: up here many people cool their homes with what we call swamp coolers. Evaporation of water is what provides the cooling of the air as it is discharged into the home from the cooling unit. This works really well, but only because it is low realive humidity of usually 20-40 percent, sometimes less.
During this first brisket/rib smoke, the cook chamber was running between 185-200 depending on several things: a couple smaller areas ran hotter, at around 225.
I've still got a few more little things I want to make better with this transformed SNP, but they're small issues. I'll fix 'em on an as-needed basis, and see how they work.
Water pan caution: during her first LPG smoke I failed to keep the water pan, shall we say...happy? Two things happened: several times I had a boil-out (no water) and glowing red pot to deal with (cold water poured into a hot pot? not pretty); then there was the dreaded overfilling of the pot to the point of boil-over when it got happy again. Well yer gears are probably turning a bit already here, and, yes it did boil-over and put out the burner. Oh, no, no, NOOOO... HOLY CRAP!!! FLAME OUT, FLAAAAAAME OUT!!!!!!!!! OK, so it wasn't quiiiiite thaaaat bad because, as my luck would have it at this particular point in time, I was actually standing there with the top door on fire box open to add some wood chunk in foil when all hell (coulda) broke loose. Still, it could've really been a very, very bad day (for my neighbors, too). Don't over-fill yer pot with H2O to save time or trips or? Yes I was boilin' off a gallon plus per hour, but from a 6 quart pot? C'mon, Eric it's only every hour or less that she needs a fill-up. Trust me, I know you don't want to go where I almost went! Waaaaay toooooo close for comfort, and yes, I did put on clean drawers after that one...
All-in-all, I'd have to say I'm VERY HAPPY with this conversion. Let me know if you want to try it. We'll look at the burner you'll be using and see if it'll fly. This is not a project for certain folks, as small children (or ?)can cause too many distractions. Remember, distractions...keep them at a minimum when dealing with new things like this conversion.
I think I'll go outside and snap a few more pics of her and post them just so everyone reading this can get a better understanding of what I did to my rig.
I was considering (had drawings too) for a charcoal & LPG hybrid conversion on my Brinkmann Gas Grill King, and also mod it to make a 6 ft tall wide body smoker. Don't wanna do it now that I've made this conversion work for my SNP.
I'll keep you posted, literally...heh.
Anyway I'm off for some pics. Later.
Eric
