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Pit Calculations/DPP Clone design questions

 
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auto5man
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PostPosted: Wed Sep 26 12 12:04 am    Post subject: Pit Calculations/DPP Clone design questions Reply with quote

Hey Guys...a few questions. But first, I should say that although I'm no stranger to bathing meat in smoke, I am a total newb when it comes to building or designing a pit. This will be a first effort.

That being said I need to ask a few questions. My pit will be a DPP style clone. Cook-chamber is one of those short and fat 500 gallon LP tanks, dimensions are 36" x 96" and its already mounted on a trailer. My firebox is an air compressor tank 24" x 46".

My first question is about the firebox to cook-chamber opening size. Using the calculator I'm getting that a rectangular opening 7" x 24" will do the trick, does that sound about right? I'm going with rectangular because I have the steel already on hand for free.

Next question is about chimney stack size. Again using the calculator planning on two stacks, one on each end....I can use either:
1) 4" pipe would give two stacks 41 inches each
2) 5" pipe would give two stacks 25.5 inches
3) 6" pipe...two stacks 18 inches

How should I be thinking as to which stack size to choose? Is the decision just based on availability/cost of materials? (and looks) Or is there some other factor to consider? Personally I like the look of those chrome semi-truck exhaust pipe stacks but I don't know the size of those pipes (?diameter).

Another question is regarding firebox size. According to the pit calculator my firebox is a little small. I'm not really wanting to change that as I already have the material on hand, but would like opinions. My feeling (guess) is that the DPP style is pretty efficient and this size firebox will work.

Assuming this firebox will work, how do I decide how close the firebox should be mounted in relation to the cook-chamber? The longer the distance, the less efficient (more heat loss over the length of the ducting) it will be so how do I decide on this distance between the two tanks? My instinct would be to make it as close as possible given that the firebox is a little small.

Thanks in advance for all advice and opinions!
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smootz
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PostPosted: Wed Sep 26 12 1:17 am    Post subject: Reply with quote

Good luck on the build. I have never attempted a DPP clone but I really admire the style. I am looking forward to watching your progress.
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auto5man
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PostPosted: Wed Sep 26 12 1:24 am    Post subject: Reply with quote

here are a couple pix to show where I'm at so far...(also to test my resizing and pic posting skills, hope I'm doing this right and not over the size limit).







Since taking these two pics the cook-chamber has been moved back about 12 inches to center over the wheels better and allow for the firebox to mate as close as possible. I'm also trying to decide if I have to cut the back of trailer off a bit to drop the firebox down as low as possible.
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Wreckless
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PostPosted: Wed Sep 26 12 1:41 am    Post subject: Reply with quote

getting ready to do a dpp clone sorta kinda. No headers, the Fb backed up right into the smoker, will see how it goes, still using the pit calculator anyways, sorta
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auto5man
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PostPosted: Wed Sep 26 12 4:22 pm    Post subject: Reply with quote

Giving this a bump, and anxious for some responses to my questions, especially about the firebox to cook chamber size. I need to decide on that figure soon, my welder is waiting on it to get started on mating the two tanks. I have been reading all the posts I can find on DPP style. Now I'm wondering if I should increase the firebox to cook chamber size to compensate for FB being a little small?
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k.a.m.
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PostPosted: Wed Sep 26 12 7:22 pm    Post subject: Reply with quote

auto5man, first advice I am going to give you is do not bump it only angers SoEzzy and he will make your thread disappear into never never land. Wink
The calculator does not really hold true to the DP style as it is designed for horizontal draft and a DP is more in and up. Your firebox seems to be a good fit to me for the tank size and dimension.
Are you going to have a convection plate or snouts running forward so the heat smoke is evenly dispersed? You could also use three 6" connector pipes evenly spaced instead of the rectangle.
If you do not plan on a convection plate or snouts reaching into the chamber do you plan on having your stacks forward? I ask this because if you connect directly with no forward diversion and your stacks are rearward then you will have a lot of cold spots forward, left and right.
Two 6" ID stacks will easily run your size cooker.
I personally need this information answered before I can say how I would set up the cooker.
I hope this helps. Very Happy
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auto5man
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PostPosted: Thu Sep 27 12 12:25 am    Post subject: Reply with quote

Quote:
auto5man, first advice I am going to give you is do not bump it only angers SoEzzy and he will make your thread disappear into never never land.


K.A.M., THANKS so much for letting me know, I had no idea. This website is a fabulous resource and I truly would hate to be offending anyone here.

Quote:
Are you going to have a convection plate or snouts running forward so the heat smoke is evenly dispersed? You could also use three 6" connector pipes evenly spaced instead of the rectangle


Yes, definitely planning on using diverter. After all the reading I did yesterday the two methods I l'm liking are either: 1) tuning plates, diverter plate 2) diffuser pipe that Mr Custom Steel posted a picture of. I can post the link to that if you don't remember how it looks...it was posted a while back. Basically it was a 6" pipe attached like a "T" to the pipes coming in the cook chamber, and ran about 3/4 length of the tank and had rectangles cut in along its length to disperse the heat and smoke.

My rough plan though is to mate the FB with the ducting and then experiment with different diversion set ups until I achieve best performance.

As far as the rectangle ducting vs the 6" pipes, I came up with the rectangle b/c I had a free chunk of steel for that. I could easily be persuaded to use 6" pipe if that is a better option.

Absolutely your post helps K.A.M, thanks so much. I have been reading your posts for years....your advice has been literally invaluable to many many builders and I thank you for taking the time and patience. Very happy to hear your opinion on my firebox, can't tell you how excited I will be to finally get that FB mated up. I actually bought the tank on the trailer several years ago, then made some basic mods....then life got in the way and the project has been languishing until now.
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auto5man
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PostPosted: Thu Sep 27 12 1:35 am    Post subject: Reply with quote

K.A.M., Here are a couple pics I found right here on the Ring. I re-post them to help show what I had in mind on the diffuser plate question:

This one shows a reverse flow type diffuser plate rolling the smoke forward under the plate then up and backwards towards the pipes placed on the ends and back (firebox side). This is a very interesting design but I'm not leaning this way. The way I envision the tuning plates would be oriented very similar to the reverse flow plate in this picture. Link to the build is posted under the picture.

http://www-rp0a.thesmokering.com/forum/viewtopic.php?p=551690&sid=879c73262eb36d5ffadb04a7cff8cd40

The next picture shows the diffuser pipe I mentioned. I really like this idea but havn't been able to find any posts yet on how it performed. Looks like a great way to diffuse the smoke/heat evenly. I wonder if it would make it harder to get temps up? Link posted under the pic.

http://www.thesmokering.com/forum/viewtopic.php?t=28921&sid=11677c8b5ab1d6fa374b75d40f604962
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idleminds
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PostPosted: Thu Sep 27 12 6:22 am    Post subject: Reply with quote

Here is what I did on my Clone

http://photobucket.com/albums/d37/freytags/New%20Smoker/

There are always small children around my cooking and having the firebox protected like that would give me alot of peace of mind, got 14 grandkids. The smoker is a propane tank 30" X 54", the firebox is a 20" 3/8 Pipe 20" long. I have no problem keeping the temp in the smoker even side to side.
I mounted it on a 54" wide by 8ft long trailer.[/img]
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auto5man
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PostPosted: Fri Sep 28 12 1:58 am    Post subject: Reply with quote

Idlemans, thanks for the posting that. I have read your build thread and seen your pictures with interest before. You did an awesome job and thanks for posting that.

Did you use any kind of diffuser or diverter plate on the inside? Do you have any trouble with hot spots or cooler zones?

I see your FB to cook chamber is a rectangle like I was thinking of making and also runs almost the entire length of the firebox. I was trying to use the pit calculator and make this opening what it specified. This would have made my opening about 7in x 24 inch, but now I'm thinking more to make it run the entire length of my firebox, more like 36in x 8in. I can always decrease that size easily if needed, but trying to make it larger on down the road would be a real headache.
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k.a.m.
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PostPosted: Fri Sep 28 12 7:54 am    Post subject: Reply with quote

auto5man, I have seen every build D. has built and he knows his diffusers. Wink The first pic is James (Whiteboycustom) cooker I helped him lay that one out. In fact the diffuser plate is leftover steel from my cooker build. Very Happy In my opinion left to right tuning plates will be hard to control unless you place your exhausts on the ends. If you place them on the rear you will be cold to the front.
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Dustyh
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PostPosted: Thu Oct 04 12 11:41 pm    Post subject: Reply with quote

I will be watching your build. I plan on building a DPP clone myself. I picked up a tank(pipe) yesterday, it is 30 inches in diameter and 55" long and 0.25" thick. I was planning on putting in a defuser plate and leaving the openings on both ends and putting my exhaust in the middle. What are yall's opinions on that idea?
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fattedhogbbq
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PostPosted: Fri Oct 05 12 6:35 am    Post subject: Reply with quote

k.a.m. wrote:

The calculator does not really hold true to the DP style as it is designed for horizontal draft and a DP is more in and up.


K.A.M., I am putting plans together for a clone (only improved) of the DP, so does this design have any type of calculator?

What do I use to to hold the design accountable?
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polishdon
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PostPosted: Fri Oct 05 12 7:55 pm    Post subject: Reply with quote

I used the "snout" pipes in my DP clone, the link to my build is in my signature. Check it out, it might give you some help\ideas.
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auto5man
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PostPosted: Tue Oct 09 12 2:56 am    Post subject: Reply with quote

polishdon wrote:
I used the "snout" pipes in my DP clone, the link to my build is in my signature. Check it out, it might give you some help\ideas.


Thanks polishdon I liked your build especially how you kept your costs down. That is part of the motivation for me too. So many of the builds on here are works of art....and I naturally want that for myself too but that's not really my goal. I have to temper my decisions in the design process to make the most of the raw materials I have on hand and hopefully end up with something functional without spending several thousand!
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