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novasbc's 250 gallon propane tank build - Page 2

Quote:
Originally Posted by novasbc

Based on my calculations, it seemed that the reverse flow plate needed to be 30.15" wide by 76.66 (tank length of 85.5" minus 8.84", which * the RF plate width of 30.15" gives me 266.53 square inches).

I think I didn't do this right, doesn't make any sense, more late night math.

I have the value of the "Area required at the end of the RF plate in square inches" (266.53 sq inches),  from DaveOmak's thread.  Do I have to calculate this with the ends of the tank as part of the equation, or do I just ignore it, and do simple math assuming that with a width of 30.15", I would have to reduce the length of the RF plate by the 8.84, like from the weld of the end-cap?

Busy searching to try and see if I can find other similar examples.  I feel I have a decent hold on calculating the height of the RF plate, the firebox minimum volume, and other things, except for how long to make the RF plate, especially since the ends of the tank are not flat, which complicates the equation.

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I think you are in the ballpark, your numbers are a slight bit high. I usually take a couple inches out of the length for the volume calculation to account for the domes and I ended up coming up with an 11 1/2" cut height for your opening yielding a 30" RF plate width. Remember a 2.5 sq-in difference in opening size is only 1% change in total size so don't worry about getting that accurate....It is total area at the dome end, not from the weld so measure to the far end of the dome to the weld (use that as 1/2 W x L) and about half way from the weld to the end (use that as W x L) and include that area in the openings, doesn't have to be perfect, just better to have it a little greater not smaller than the FF/CC opening.

Quote:
Originally Posted by LenDecaturAL

I think you are in the ballpark, your numbers are a slight bit high. I usually take a couple inches out of the length for the volume calculation to account for the domes and I ended up coming up with an 11 1/2" cut height for your opening yielding a 30" RF plate width. Remember a 2.5 sq-in difference in opening size is only 1% change in total size so don't worry about getting that accurate....It is total area at the dome end, not from the weld so measure to the far end of the dome to the weld (use that as 1/2 W x L) and about half way from the weld to the end (use that as W x L) and include that area in the openings, doesn't have to be perfect, just better to have it a little greater not smaller than the FF/CC opening.

Thanks, that is a good explanation.  I think I'm going to work something up in my calculator, and include the basic ideas in a help popup or something.

I have found this Calculator very helpful  i purchased a 288Gal Propane tank yesterday and i will slowly start my project in the next week or so.    good luck with your build.

http://feldoncentral.com/bbqcalculator.html

Quote:
Originally Posted by BlackBarkBBQ

I have found this Calculator very helpful  i purchased a 288Gal Propane tank yesterday and i will slowly start my project in the next week or so.    good luck with your build.

http://feldoncentral.com/bbqcalculator.html

The calculator below, is an updated and modified version of Feldon's... Takes care of a few problems Feldon's has when building a reverse flow smoker.....

Ah very good. Thanks for the link.
Quote:
Originally Posted by BlackBarkBBQ

Ah very good. Thanks for the link.

Yes, thise calculations are what I have been going by, and as you see later in the thread, I dhared the program I built in order to try and make it easier.

Finally getting a chance to work on this again, haven't been out of town where my project has been sitting since Christmas.

• I'm starting with tank upside down to make my cuts for the firebox.
• I'm going to make the firebox opening for 11.9" based on my program that implements DaveOmak's formulas.
• It was mentioned by somebody to increase this to 12.25" to leave room for a baffle.  I don't know what this refers to, honestly.  I assume this another term for the reverse flow plate.
• I can always open it up further if I have to, so I guess I'll pick the smaller of the two for now.
• I'm still highly unsure of how the reverse flow plate, FB/CC opening / Firebox are all supposed to go together.
• Once I get the opening done, I can double check my numbers, that I can slide a reverse flow plate in and it should be 30.15".  I'll go purchase the sheet metal for this, and get it cut to the proper size.
• Slide the plate in, with it being at the top of the FB/CC opening, and weld it in place.
• I guess I'm supposed to cut the end of the plate to match the dome curvature?  Or does the interaction of the firebox somehow help seal this?
• I'm not sure how the fit of the plate is going to be compared to the FB/CC opening.  But, I assume the firebox will be welded to the end of the reverse flow plate, so that it forms a solid surface

Ribwizzard's post, http://www.smokingmeatforums.com/t/172521/novasbcs-250-gallon-propane-tank-build#post_1275581, still has me confused, unfortunately.  He says to slide the plate in before welding in the firebox, makes sense.  However, if I have the plate in there, how can I later reach in with a torch, and "cut opening into firebox".  By definition, the plate is already there and in the way?

I'm just going to move forward, and get the FB/CC opening cut today, since I have to make some progress, and hope I can muddle through the other aspects, and start understanding how they all go together.  I try to find pictures to answer my questions, but haven't quite found the ones that really show me what I'm wondering.  Tonight when I lose daylight, I'll do some more searching.

You don't have to mark from inside the cook chamber if you already have the RF plate in place. You can mark from the outside of the cook chamber and cut inside the lines. Make the difference the wall thickness of the cook chamber, if that makes sense. Remember, none of this has to be exact, just reasonably close such that you can get it welded back together.

Now that I have the FB/CC opening cut, I'm still trying to think of how it goes together.  I wonder if it wouldn't be wise to make the reverse flow plate and the top of the firebox the same piece of metal.

So, get the plate cut long enough to stick out of the side of the propane tank long enough, and then build the other sides of the firebox onto the exposed RF plate.

Now that I have it open, I can see there is an internal band at the weld, I guess for extra strength, but it will make it a bit more complicated to slide a plate in.

Is there any reason

Quote:
Originally Posted by LenDecaturAL

You don't have to mark from inside the cook chamber if you already have the RF plate in place. You can mark from the outside of the cook chamber and cut inside the lines. Make the difference the wall thickness of the cook chamber, if that makes sense. Remember, none of this has to be exact, just reasonably close such that you can get it welded back together.

Pictures.  The size of the plate needed seems to match my calculations, fortunately.

I've decided to put an angle to the reverse flow plate down the center to the drain. Anybody have suggestions as to the maximum angle I should do? I imagine if I make it too much of an angle it could cause unpredictability with the smoke flow.

When I built mine( I used a 500gal tank), I used a piece of channel down the middle and attached a piece of plate to each side for the reverse flow plate.  It made handling that sized piece of steel considerably easier. We ended up welding handles to it. It also left a flat spot to attach the drain.  I did use the top of the firebox as part of the reverse flow plate as well and have seen no ill effects other than that end of the smoker does run a little hotter but sometimes that is a nice thing as long as you know it.

Another thing that I have learned is that level is everything.  I had to start to think that hot air flows up just like water will flow downward.  If you have one end or the other of the reverse flow plate too high it will trap heat at one end or the other.

Quote:
Originally Posted by jarjarchef

Sitting still you are ok, but what if you hit a bump. Then the whole load weight will increase, even if just for a split second.

This does not make any sense to me. How could hitting a bump make the weight on a trailer increase???

Seen tires getting mentioned here. FWIW if you were to go to Discount Tire and buy there better trailer tires, they will be radials, you will be able to get a Road Hazard Certificate with them. The industry standard on tires is 10 years....which means that for 10 years you will not have to worry abut damage to the tires....

Quote:
Originally Posted by inkjunkie

This does not make any sense to me. How could hitting a bump make the weight on a trailer increase???

Seen tires getting mentioned here. FWIW if you were to go to Discount Tire and buy there better trailer tires, they will be radials, you will be able to get a Road Hazard Certificate with them. The industry standard on tires is 10 years....which means that for 10 years you will not have to worry abut damage to the tires....

Inkjunkie, evening..... Think of it this way.... If you suspend a 2 x 4 across a span, so you can stand on it.... and it holds your weight, then jump on it and it breaks...... It's the same situation when the trailer hits a bump, the road is coming up to meet the load... the springs compress and push upwards..... Force is applied upward on a bump..... Force applied downward when you jump....
Quote:
Originally Posted by DaveOmak

Inkjunkie, evening..... Think of it this way.... If you suspend a 2 x 4 across a span, so you can stand on it.... and it holds your weight, then jump on it and it breaks...... It's the same situation when the trailer hits a bump, the road is coming up to meet the load... the springs compress and push upwards..... Force is applied upward on a bump..... Force applied downward when you jump....
That is what the suspension is for...
Quote:
Originally Posted by inkjunkie

That is what the suspension is for...

And that's why the suspension collapses under the added weight..... the springs do what they were intended to do.....

It's not that the trailer gets "heavier"... It's the inertia or "bodies in motion" or something like that....
Quote:
Originally Posted by DaveOmak

Inkjunkie, evening..... Think of it this way.... If you suspend a 2 x 4 across a span, so you can stand on it.... and it holds your weight, then jump on it and it breaks...... It's the same situation when the trailer hits a bump, the road is coming up to meet the load... the springs compress and push upwards..... Force is applied upward on a bump..... Force applied downward when you jump....
problem with this is the load is not jumping up and down. Any impacts are getting absorbed into the springs, which are designed out of spring steel for this very reason. Take the guy carrying a ton of pellets in the bed of his truck. The bed is suspended in 4 or 6 areas. Using the above info the bed would probably collapse. But throw the suspension in the picture and well....

Ride a scooter over a 4x4 @ speed, it will go airborne even with suspension. If it flies, it has been loaded well above the static weight. How much you need to worry about that is only a function of how you drive when pulling it, ease around and it is not problem, haul ass over rough roads and things can break. Think of it like all the energy put into it to go forward on the straight and level, everything is going smooth, then you stick a sharp angle in the path forward, that energy gets hit with a vertical component, brace up, it's going to get interesting. The amount of force is directly related to the speed since it gets its energy from the momentum of the moving weight if that makes sense. Crusty old retired engineer just trying to help.

Quote:
Originally Posted by LenDecaturAL

Ride a scooter over a 4x4 @ speed, it will go airborne even with suspension. If it flies, it has been loaded well above the static weight. How much you need to worry about that is only a function of how you drive when pulling it, ease around and it is not problem, haul ass over rough roads and things can break. Think of it like all the energy put into it to go forward on the straight and level, everything is going smooth, then you stick a sharp angle in the path forward, that energy gets hit with a vertical component, brace up, it's going to get interesting. The amount of force is directly related to the speed since it gets its energy from the momentum of the moving weight if that makes sense. Crusty old retired engineer just trying to help.
Hmmmmm....no...Have put close to 300k on 2 wheels. Have hit more than 1 chunk of lumber in those miles. Last one was on my GSXR1000 at 70 mph and the bike never left the ground...
Think I will respectfully bow out of this conversation now.
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