6" opening to 8" stack

[valleyman]

I have a 6" stack and I'm thinking going to an 8" diam to improve performance. Trouble is that I have permanent 6" flue pipe cemented into the back wall. Would it negate the benefit of an 8" diam. stack if I keep the smaller opening? The stack is 10' tall.

My block evaporator is about 22" W x 48" long

[Smitty]

valleyman,

8" pipe should help even with the 6" elbow,probably not as well as with a 8"
elbow, but it will increase your draft. hope this helps you out.


best regards,
Allan Smith:)

[Bemis]

I'd maybe try adding 4 more feet of stack to the top as a possible solution to increase draw. I'm not sure the 8" will do much for you with the 6" restriction.

[maple flats]

The 8" will help significantly without changing the elbow, but not as much as changing it. I'll guess you will improve draft between 15-25% while you would gain near 40% to change the elbow. You would also gain a good amount by adding the 4' suggested above. What makes you think the draft in too little? Do you not get a huge inferno with the air inlet full open? Do you have a draft blower? Does it create back pressure? At your 10' tall you should already be good however. The traditional formula is 2 x length, you are at 2.5 x length now. Does your stack get down drafts off trees or an adjacent building or a hill?

[TapME]

valleyman, is that pic of the inside of the evap under the pan? You sound have about 2'' of space under the end of the pan with a drop about 6'' from the elbow getting larger to acomadate the flue gases and the stack pipe. This would help force he fire up under the pan and make it boil harder. It woould also create a venturi effect and create more draft up the stack.Just my oppinion.

[valleyman]

Last year was my 1st season w/ this setup. The 1st few boils were'nt getting the two rear pans boiling. Seemed like the system was chokoing. So I went in and replaced the full firebrick floor with splits to create more more air space below the rear pans. I noticed an imediate improvement and I got the third pan boiling strong and the last pan rolling boil.

So I was thinking this season to go with a larger flue mhoping it would make all 4 pans go with a rippin boil.

Tap Me,
I included a diagram of aprox. how my set up is. The pans mmay even drop in a bit lower.

So if I add another 4" to the block walls which will make the pans sit higher, that'll be better.? When I was designing, I saw that all the "real SS evaps" have the flue pan really close with little space for the hot gasses so I tried to mimic that.

[valleyman]

Heres a diagram that goes w/ my last post.

[TapME]

having the stainlees table pans throws a twist in to the picture. (I forgot you had them). The larger stack would help to create more flow(like was stated here)without changing the elbow. Some additional hight could help to get the pans boiling. You should try shaping the back of the arch so it has a tapper and gets smaller as it comes closer to the rear of the pans( somewhat like a river when it come to a narrow gorge it speeds up and gets faster) is what you want to do. A question what happened when you gave the fire more air when the space below the pans was smaller?

[valleyman]

Tap Me,

To taper the walls in, I think I need to go up another 4" and add another row of firebrick before I can do the taper.

Last couple of boils during 2010 season when I gave the arch more airspace it got all 4 pans boiling.

So I dont know if I should leave well enough alone or tweak it even more to see if I get it even hotter under the rear pans. If I do nothing, it'll put out OK.

I'm starting to get the itch to mess around with it again.

I may just get some 8" duct pipe and have it on hand and leave the 6" elbow for now.

[TapME]

sounds like your on top of it, just make sure your wood is dry and the draft door is wide open. I do not use a draft door and my fire gets real hot. You know that your draft is good when you have no ash to take out of the arch after boiling all season. Bring the water hoze over fill it up and give it a try it does 2 things. Makes you fell better and takes the edge off of changing things.