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 Draft problems

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wsi777



Posts : 3
Join date : 2015-02-28

PostSubject: Draft problems   Fri May 01, 2015 12:32 am

Hi
I need help.

I have just made Rocket Stove similar to the last one ppotty1 made.        ie  L 30cm  x W  37 cm  x  H 50 cm.
The firebox the same size with the opening at the top and a door at the side for the ash tray
The  riser is  13 cm in diameter &  insulated  with the ppotty1 vortex design.   I have 3 air inlets  (8cm x 3cm) coming through the heat exchanger to preheat the air one of which is going into the heat riser.  The air comes in at the bottom sides  of the firebox and exits at the top.

When I tested it I have no draft going into the riser and the smoke comes out at the top of the firebox (no downward draft, no draft at all). When I sealed the top door of the firebox it smothered the fire
Does the firebox need to be smaller than the heat exchanger to create the draft?  

I would appreciate any help

Thanks

Peter form Ireland
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gadily
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PostSubject: Re: Draft problems   Fri May 01, 2015 3:31 am

peter could you put up a few photos so we can see the build ay all ?

as this would help us to understand more

heres the link if you need it at all

just right click on the link open in new tab is best way to do it

http://woodstoves.forumotion.co.uk/t566-posting-pics-and-youtube-videos-on-site



try this way if you want try lighting inside of the 2nd burn chamber as sometimes you need to get this part going to suck properly up the vortex tube as ive come across this with my build

https://www.dropbox.com/s/av6jpjqew3wacfz/20140607_212922.mp4

? how low is your exhaust to chimney on the system

and my biggest mistake was have you got a decent chimney about 6ft high as the chimney has an effect on the rocket stoves

i will leave this post here for now but will move it to show us your stoves later on
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wsi777



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Join date : 2015-02-28

PostSubject: Re: Draft problems   Sat May 02, 2015 3:33 am

Hi Gadily

Thanks for getting back to me



Starting the fire in the riser has helped and I extented the flue to 6 feet which also helped

My vortex is not great and the fuel is burning rather than gasifing

The flue exit from the heat exchanger is 3 inches from the bottom.

When I open the firebox door there is no downward draft to the riser

The inlet going to the 5 inch riser is 4 inch x 4 inch. Do you thing that makes a difference?

Thanks

Peter
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gadily
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PostSubject: Re: Draft problems   Sat May 02, 2015 5:57 am

peter im not familier with the design so can you do a drawing or explain the build and how it goes to each system

there was ppottys build of this



if that helps to explain much better

a 5 too 5 would have been better

http://woodstoves.forumotion.co.uk/t219p15-start-of-my-rs-build

mine is built 4, 3/4 too 4" using a flick of ppottys this speeds up the rush within the vortex

i just know im going to be asking dimensions of the whole system

need to know firebox size and how your pipes run and what size are they also have you reduced there size to give enough space for thermal rise of air within the primary air input of the system i used 3/4" ppotty uses 1"

riser is 5 but your 2nd burn tube is 4x4" which needed to be bigger
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caotropheus
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PostSubject: Re: Draft problems   Sat May 02, 2015 1:51 pm

Peter,

I saw your videos on Youtube. If you make videos and/or pictures of your projects, please post links here into the forum so we can see better understand what happens. Are these your videos?

https://www.youtube.com/watch?v=A98UhDgpcJo
https://www.youtube.com/watch?v=xg0LX16n3oM


Can you please make a video with details of the stove, inside and outside, including air supply dimensions, air and fire flow, all sorts of dimensions, riser tube height in relation to combustion chamber, location of chimney in relation to combustion chamber, etc Take a measuring tape and measure as you make the video of the details. If you have a stove with a glass to see the fire, make a video of the fire, at night, so we can see the combustion and identify potential problems. Take your time to make this video, even if it takes several minutes. During the stove build, did you run preliminary tests before continuing to the next phase, for example testing the rocket stove core?

For some reason you are stalling the fire, free flow of combustion products is not occurring, lots of smoke is produced and temperatures are not high.


Last edited by caotropheus on Wed May 13, 2015 12:41 pm; edited 1 time in total
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gadily
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PostSubject: Re: Draft problems   Sat May 02, 2015 8:33 pm

peter from what i can see it looks like you have used 1,1/2 x 2" inputs for all of the air slots

the secondary air is ample enough with just normal 1"x 1" or using 1,1/2" round tube as ive found out

im not sure how you have built the system but ive drawn a diagram using paint program on windows pcs



the bottom pic on the left is wrong due to when reducing a bigger pipe to a smaller pipe you are actually speeding up the flow into the round tube which makes a better vortex inside of the pipe

if you are wondering why i have a light blue drawing to the top is that i would use the thermal of air rising within the firebox of the heat that the incoming air would get however 1,1/2" is too bog it would need to be reduced down to 1" or 3/4" as you are wanting the push of air to push the flames into the vortex tube

the glass air would also need to to come back down over the glass
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les, slight limp



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Join date : 2015-02-27

PostSubject: Re: Draft problems   Sun May 03, 2015 9:35 pm

Hi guys, don't forget ppoty1 has a positive draw cowl on his chimney, i will fit a positive draw pot suitable for a wood burner on my chimney, lighting will be much easier, regards les.
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wsi777



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PostSubject: Re: Draft problems   Wed May 13, 2015 4:43 am

Hi

Thanks for you help

I have done a new video which I hope will explain my design and hopefully identify what the problem is


Peter
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gadily
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PostSubject: Re: Draft problems   Wed May 13, 2015 6:50 am

hi peter ive tested the secondary air so heres my results

my videos are downloadable and play ok within vlc media player

http://woodstoves.forumotion.co.uk/t62p15-secondary-air

4 3/4" reduced down to 2 1/4"

like yours via the left side

https://www.dropbox.com/s/7bhjplsuiazcrzv/DSCF5139.AVI

the right side following the flames into the vortex area

https://www.dropbox.com/s/g1ek1luxw4uw4bd/DSCF5137.AVI?dl=0

however ive noticed yours could be canceling the vortex action of the stove



your vortex tube 3" x 1 1/2" i believe is too big 1" square tube to 1 1/2" round tube is ample enough

i tried to smaller rise it by near on equaling the height of the firebox to the system 17" vortex tube 9" firebox nearly 10

https://www.dropbox.com/s/1i5rl6ya8qjculf/20140517_202633.mp4

https://www.dropbox.com/s/hd4ikrcklyxwl4d/20140517_204501.mp4

whats going on is you have equalized your firebox to your exchange heater in effect you are in one way stalling your system as the firebox chamber begins to build a fire within your firebox chamber and your fire chamber ends up hotter than your exchanger
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caotropheus
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PostSubject: Re: Draft problems   Wed May 13, 2015 12:52 pm

I think you have to make a riser tube and heat exchanger taller than the combustion chamber (fire box). Try to make the riser tube at least twice at tall as the combustion chamber. Try as well to place the chimney exit 5 to 7 cm above the bottom of the combustion chamber, it will help greatly start the fire and keep high temperatures in the stove.

By the way, the hottest place in the stove is always the combustion chamber, not the top of the heat exchanger.
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gadily
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PostSubject: Re: Draft problems   Wed May 13, 2015 6:35 pm

there is another way by reducing the mass of air being moved within your riser system from watching the vids and my own tests

yours is a 5" riser to a mass of 14" square works fine with higher systems as more air is pushed upwards but with systems of equal height the air must be less within the exchange unit

the easiest way to test this is by building a layer of bricks up to the top therefore reducing the mass of air within the exchanger that has to be moved within the system
then relight the fire and test again thats if you dont want to cut it up

this is something ive noticed when building the smaller rocket stove
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T2H
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PostSubject: Re: Draft problems   Wed May 20, 2015 5:32 am

I think you are right about making your entrance tube into the riser larger, you have quite a large volume of fuel your dealing with.

As well consider insulating three of the walls of the fire box, even the bottom end.
Looks like your air delivery is done quite well.
You will need your main air delivery air tight so you can shut down the main air almost all the way and then start using your secondary air controls.
The secondary air really has its best results once the stove is up to optimum temps.

During the initial light up, you should not have the secondary air open and as well it need to be air tight.
This will help in inducing a better draft from the start and as well reduce any blow back.

If the secondary air is open or has any drafting in the initial start up it creates a tug of war between your open firebox and the chimney.

Very nice stove mate, well done.

In order to insulate three of the walls you could form a thin gauge outer casing, will have to make your entrance tube a bit longer to add for the extra insulation around the walls.
It really takes some tinkering with the air controls and getting used to figuring out what makes your stove perform the best.
Also have to agree with caotrapheous on his observations on the riser tube being twice as tall as the firebox, this will help in drafting.

Gary B had the same results you did on his first tests, once he was able to learn what the stove liked he performed like a champ.
Beautiful stove!

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