Reverse Flow First Time Builder.

Discussion in 'Reverse Flow' started by cobrafnd, Apr 28, 2011.

1. cobrafndNewbie

I picked up a piece of 24" pipe today that I found on Craigslist that is 86" long.  Pipe is 3/8" thick.  I plan to use it for the firebox as well.  I have a few questions to get me started.  I will be posting pics as I go.

How high should the plate be from the bottom of the pipe?

Where should I cut the pipe for lenghts?  I was thinking a 30" firebox, and that would leave 56" for the smoker.

On a smoker this size, what size pipe should I use for the stack, and how tall?

I can't wait to get this thing started, but have to get some plate steel first.

2. fourashleysSmoking Fanatic

Nice get on the pipe. Check the pit calculator to answer alot of your # questions. Looking forward to some pics.:welcome1:

4. cobrafndNewbie

Ok... so smoker is 64.5" long and firebox is 21.5" long.  My sq" opening connecting the 2 is 78sq".  So on a 24" pipe, I can take the....

width of the steel plate x height off the bottom of the pipe x .4 = area of opening... I will have to do some experimenting on that one to see what it will take to get the 78sq".

Thanks so far.  I am at work, so can not get on photobucket to upload a pic!  Will get the pic of the pipe up in the morning.

5. tom37Master of the PitOTBS MemberSMF Premier Member

Nice score on the pipe.

The general rules are to build it close to 1/3 rds. Like the firebox ending up 1/3 the size of the cook chamber.

The calc numbers are a low end base to go from. So if it says you need 78 sq in and you were to end up with 90, its not going to hurt ya. You can always choke down the fire vs fanning it to keep it a decent size.

To be honest, I really can't help on the math. I always cheat and use one of the circ calc's online. There are several that will give you the cord and sector area ( I hope I named them right) which is the ones you will need since you should end up with an egg shaped hole from the firebox to the cook area.

Get ready man, I built one from 3/8 pipe 16" dia and 42" long. I'm here to tell ya, its Heavy, big time. I had to use 1/2" wall pipe 20" dia for the wheels. The one time I took it somewhere I had to have 4 of us to roll it up the ramp of my mowing trailer. I believe there is a link in my sig, under reverse flow build that shows my progress pics.

7. cobrafndNewbie

Oh.. I definitly plan for it to have wheels... even if it is just for pulling around the yard with the 4-wheeler.  I have an old boat trailer that I may use.  I am not sure if my calculation above is right, so someone correct me if that is wrong.. just seen online where calculating an oval is lenght x width x .8, so a half oval would be x .4

Here is a better calculator for that. http://www.1728.com/circsect.htm

5 1/2" up from the bottom of your pipe would give you a 78.2 sq.in. opening.

9. cobrafndNewbie

That's what I am talking about!!! Post up the link, and do the math!

Great help people.  Thanks so much.

11. cobrafndNewbie

try that!

Last edited: Apr 29, 2011
12. tom37Master of the PitOTBS MemberSMF Premier Member

Thank You Joel.

I was looking for it but in my new browser all my fav's are in different places.

If you take the link minus the img tags and enter it in the insert image tab under import link it will show in the post like this.

Nice score on the pipe man.

I have spent a lot of time there recently.

14. hardslicerSmoking Fanatic

now that thing is going to be heavy........nice find there brother!

15. cobrafndNewbie

Thanks everyone... still waiting on some prices for plate.  That and working 12 hour days Sat. Sun. and Mon. has not helped either.  Has anyone checked prices of steel lately.  I am wondering to compare this machine shops price with.

Thanks!

16. tom37Master of the PitOTBS MemberSMF Premier Member

I just bought a 4x10 sheet of 16 gauge sheet at Metal by the foot. 140 bucks. Now thats a little high since they are a (we got it, you want it, so you pay what ever we want) kinda store.

From one of the bulk suppliers I believe the price was about 80 or 90.

I had a one off job for some plasma work and I needed the sheet kinda spur of the moment. And since I don't have a lot of room to store it, I went ahead and bought it from them since it worked into my work schedule.

I do believe that the scrape yard is your friend when it comes to the heavy plate.

I agree with Tom. Check the scrapyard first if you can.

18. cobrafndNewbie

Ya... got prices from them today... for a piece 21x80 for the plate in the bottom, and four 24" circles, it was 275.00.  Going to check a couple other places in the next few days.

19. cobrafndNewbie

Ok... another question... Got all of my plate and pipe for the stack, but all the guy had was a piece of 5" pipe for the stack.  With the calculator above, that makes the stack about 24" tall.  I want it taller than that..... if I were to put like a 5 to 4 reducer on the top of it, would I calculate it as a 4" pipe, since the opening to the atmosphere is only 4", or would it not work that way?

Thanks,

Kevin

20. tom37Master of the PitOTBS MemberSMF Premier Member

Oh boy, I'm not sure on the stack question. We better leave that one to the guys that have formal training in figuring mass and flow with surface tension. LMAO. Usually at this point I just try it and see what happens.

A taller stack isn't going to hurt you at all. I don't think. It should make it draw better, I believe.