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PBC Upper Vent Modifications - Version X

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    PBC Upper Vent Modifications - Version X

    Why 'version x'? because I suspect I'll be adding a few more to this thread - ultimate goal is a controllable vent like Jerod's.

    So, in the spirit of "If it ain't broke, fix it till it is", I've decided that my PBC clearly needs an upper vent to create a more controllable temp (not just the hot and hope that we live with in the stock version - although I have no complaints!). My goal is to cut down the trailing temp descent that can happen as the cook progresses, that then require a big temp spike through cracking the lid to get the cooker right back up to the 275 - 310 cooking zone.

    This first stage is really about keeping it stupidly simple, and seeing if it works. Knowing that simply removing a bar can affect the temp significantly, additional 3/4" holes at the bar level will probably work with most single meat cooks. (Lots o' meat - 5 briskets or whatever, will need something more engineered). I plan to drill 3, space them at middle back and middle each side as you look at the front lower vent. Nothing on the front edge.

    Question arises about how to control the airflow through those holes and hence controlling the temp. 3 solutions I'm going to test:

    1) Plugging one, two or three. It seems like the PBC only needs a marginal increase in airflow to get to a consistent higher temp, so maybe unplug each hole in turn as the cook progresses. How to plug the holes? Here is my best 'simplest' idea:

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    A wine cork. I'll coat it with some flax seed oil, but it shouldn't burn (temp won't be high enough, and cork can't maintain a flame to burn itself). (apologies for the pic angle. For demonstration purposes, I'm using the existing bar holes). Finally, if it does burn, I'll open some more wine - problem solved and situation improved.

    2) How about more control for each vent hole: 2 Simple ideas:

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    The carved cork. Chop down one the chopping block a couple of times and you've got a smaller hole. Took about 5 seconds. (and another bottle of wine! Engineering is one hell of a career choice if you ask me.)

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    The round 1" magnet. This can just slid up and down to partially cover the hole. 6 were $2? at lowes. Magnets fail with higher temps, so we'll see how this lasts. The curvature of the barrel obviously affects the seal, but the gap is so small I fully expect a little bit of grease build up will fill in the gap.

    So with the two finer adjustment ideas, again I think it would work for adjusting as the cook progresses, probably not necessary for the first hour or tow unless a lot of meat is used or a higher temp required.

    Anyway. That's the plan. Wish me luck - I'll post the results!

    Matt
    Last edited by mtford72; December 5, 2014, 12:20 PM.

    #2
    I love this post already! Dead cheap (but very qualified) solutions. Way to go. The only 'drawback' is that one must keep a fully stocked wine cabinet at all times. And they say engineering is easy...

    Looking forward to the next posts.

    Comment


      #3
      Looks good. There are lots of different air flow valves available pretty inexpensively, here is a quick one that should meet the criteria. A small needle valve would be cool too if you could get one low profile enough.

      Comment


      • mtford72
        mtford72 commented
        Editing a comment
        I'm thinking a larger bore - maybe 3/4 of a inch valve should work. A quarter turn ball valve would be perfect, then attach a chimney of 3/4" pipe to create draft. The quarter turn would be a good visual of how open the valve is from a distance. (basically the conversion Jerod did).
        All the ones at Lowes have a teflon membrane on the ball and consequently a max operating temperature below 300F. I might need to do a little searching.

        BTW - thanks for putting me on to that website in your post - I'll have a dig around there.

      #4
      Nice. My little magnets I have to cover the holes when trying to achieve lower temps have held up nicely.

      I realized I maybe should have went 3/4 with mine. I think if I crack them up at start up, they do fine.

      Comment


        #5
        What if you added holes to the lid instead of the barrel? Then placement is adjustable (just rotate the lid) and curvature of the barrel does not impact the magnet seal.

        Or is it more important for holes to be on the side of the barrel?

        Comment


          #6
          Hey Jeff,
          Timely question - I'm moving on to Ver 2 (in my head at least - more on that in a moment). As for vents on the lid, that seems to be the conventional location for barrel smokers, and both your points are valid. But there are two unique features about the PBC that steered me away from that idea.

          The two are the operating temperature and the moist environment. The PBC seems to achieve the odd combination of a hot temp and moist environment. I believe that comes from the air being essentially 'static' within the system. My concern is that a lid vent may disrupt that, creating much more draw or setting a more active convection cell within the PBC. Either of which would change the moisture level, as more air would be leaving through the top of the chamber - I'll call it 'exhausted convection'. I have absolutely no scientific basis for that, but its a strong enough hunch that I don't want to put holes in the lid.

          I should note, that most conventional UDS have the holes in the lid, and then control through the intake valve. However, they also may well have water pans and baffles, and typically cook at a classic smoking 225 or there abouts.

          So, Ver 2, essentially involves dropping the vent holes to just above the top of the basket, and using a nipple pipe to reach the basket edge. The idea is that the air is drawn up through the basket and vented just above basket height. I think that this would cause the fire to burn a little hotter as the coals are getting more airflow, but not disrupt the air in the chamber by creating a convection cell. The 'block' of air surrounding the hanging meat with all its smoky, moisty goodness would be made hotter through a higher percentage of radiant heat, rather than either circular convection or an exhausted convection.

          I'll sketch something out and post it.

          Matt

          Comment


            #7
            Hey Matt,

            Makes perfect sense, and while you may not have scientific basis it is clear that the PBC is a unique animal in the smoking world and sets the bar for all others.

            Being the PBC novice that I am (first cook today), it is also evident that you (and the other experts here in The Pit) have vastly more experience and knowledge of the process, and I am certain that the quality of today's smoke would have been much lower without inputs from this amazing community.

            Stocking my wine cabinet in anticipation of your post...haha

            Jeff

            Comment


              #8
              Before I drill, any thoughts?

              So, Ver 2, essentially involves dropping the vent holes to just above the top of the basket, and using a nipple pipe to reach the basket edge. The idea is that the air is drawn up through the basket and vented just above basket height. I think that this would cause the fire to burn a little hotter as the coals are getting more airflow, but not disrupt the air in the chamber by creating a convection cell. The 'block' of air surrounding the hanging meat with all its smoky, moisty goodness would be made hotter through a higher percentage of radiant heat, rather than either circular convection or an exhausted convection.

              Comment


              • Spinaker
                Spinaker commented
                Editing a comment
                What size bore are you going to use?

              #9
              3/4" inch. The chimney is 1" dia. There are two, opposite sides.

              Comment


                #10
                I'm probably wrong, but just trying to logic through this. The air heats up and rises and with the vents at the top they escape, pulling some air in through the intake. Opening the lid lets more escape, pulling fresh air across the coals. How it is now the smoke swirls all around the barrel, I know because when some smoke is rolling you can watch the air come in and see how the smoke swirls around. With another vent at the bottom, it would seem that, unless restricted, the new pipe would act the same as the existing intake. If the pipe is restricted, through size and bends, then it shouldn't act as an intake because it is easier for air to come in through the existing intake. As you get more air, which gets hotter and expands and tries to exit, the same restriction that kept it from being an intake would likely prevent it from being an exhaust as it could be easier for the air to exit the existing holes or even the intake. If these two weren't matched right you will probably not get much change at all.

                Holes at the top make it easy for air to escape, pulling in fresh air from the bottom. Right now there are holes on both sides so the smoke hangs up there with the meat until it is forced out. If the opening at the top isn't restricted enough you might just blow the smoke straight out, and while the fire might be hotter, the area near the meat won't get as hot. For example when the temp is way down and you take off the lid the temp at the meat drops because hot air is escaping, but the fire is being stoked so when you put the lid back on it skyrockets.

                We also know that warm air rises, so if the exhaust is at the bottom you could create a situation where the air is swirling up to the meat and back down to the coals to exit, this could bring a lot of ash up to the meat.

                All that said, I would think that holes near the existing ones in height would be ideal. I think your major challenge will be in how you prevent your new exhaust from becoming another intake if placed at the bottom.

                But again, i'm probably wrong

                Edit: I'll add that when you are getting late in the cook and you want more heat, you can take out the rebar and that works well, putting them at the top should be a proven way to do the same thing without having to remove the rebar.
                Last edited by _John_; December 9, 2014, 06:18 PM.

                Comment


                • mtford72
                  mtford72 commented
                  Editing a comment
                  I must admit, I didn't consider the idea that it could turn into a intake. I now want to go back to the original plan of small holes at the top, but that's so mundane! (and effective, and cheap, and simple, and sensible).

                  I planned for a couple of small elbows to point the bottom of the chimney actually at the basket. I suspect that once the fire is going, a draft will get established and the chimney will indeed vent.

                  I'm fairly sure recklessness will get the better of me, and I'll try out the pipes. Worse comes to worst, patching the holes should be straightforward. Then I'll go back to simpler, vastly more effective and reliable version.

                • _John_
                  _John_ commented
                  Editing a comment
                  Nothing wrong with testing it out, might be good to have an intake on the other side if it ends up working that way, will be really easy to hit 325+

                #11
                I think I would put the holes in line with the existing ones. But I would put them at 3 and 9 (if the existing ones are at 12 and 6) I'm thinking maybe that would produce more uniform vertical draw within the barrel. I think there is plenty of smoke in the barrel without having to worry about the smoke just flying right out of the barrel and not flavoring the meat. I would put them on top at the same level as the other holes. Keep us posted.

                Comment


                  #12
                  Tying in to John's comment, the goal is to get a) the variance out of the system - one cook seems to be mid 200s, others 310. b) give a bit of flexibility for crisping, etc. c) gear up for big cooks - I've done 4 briskets at once. That just requires more flow, plain and simple. (see Jerod's posts). The only way to achieve this was cracking the lid for the whole cook.

                  I realize I am describing this as a 'need', when really just a desire to fiddle!

                  So I'll play, test and see.

                  Comment


                    #13
                    I couldn't help myself. I drilled the holes, added the pipes. It works, but I'm stuck thinking 'why the hell did I drill holes in my lovely PBC?" Pics and graphs to follow.

                    Comment


                      #14
                      I love my set up MT. Like you said, especially when you load her down.

                      Comment


                        #15
                        Im thinking about doing the same thing to mine.

                        Comment

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