I was told that 15 micron would remove nuisance dust. Some of these go down to 0.3 micron (95%). These might be best with a small engine.
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What about a standard vacuum cleaner bag? It would be convinient if that would work.
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I second that idea. There are pleated conical HEPA grade filters already made, with a good fitting attachment, cheap.
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Probbly not fine enough for you char application, though i was thinking of putting a good size box simular too the one on top your radiator, and placeing one or more furnace filter in series just before the air cleaner houseing/ mixer. I was allso thinking about building something like mr. Max Gasman talked about, a big surface area one on the roof. maybe like about three inch thick, by the roof width and lenth out of the wind low profile, maybe could mount under frame on a pickup truck with more ground clearence, got too figure out a design yet though may maltable smaller units in paralelle too keep out of the wind drag. Any units easy too clean is the other varriable that has too be equated. WORKING GOOD, all your expert wood gas designs.
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Kristijan asked, “what material are they made of?”
The invar shadow mask is composed of the nickel-iron alloy invar. Invar - Wikipedia
Invar parts and prototypes: Custom CNC Machining
I have some that has been laying out in the yard for about six months. The holes are very small, and close together. I can see right through it. I removed it from a Cathode Ray Tube.
My plan was to try it as a wire mesh dome in the flame of a TLUD stove, hoping it would glow red as in this 5 second video: https://www.youtube.com/watch?v=jK3UTe1Lxqk&feature=youtu.be
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Ray, thank you for proposing this. This might me a suitible candidate for a hot filter! Culd be placed right at the drop box.
Allso, l like that video a lot. You got to trying it your self?
I finished the automixer today. This is what l came up with.
The membrane is a thick plastic foil, reinforced with a thin metal disc.
The valve is a kind of a gate valve. The idea was that l wuld make it compact and as simple/foulproof as possible, and this seems superior to a buterfly valve in those aspects. Reality will be shown soon 
On the video it seems like l am holding the automixer in a huricane, but in fact l was only blowing on that small hole and as you can see it can esyaly move the plunger up and down. Looking forward to test it.
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Is it possible to show some pictures of the mixer in it’s separate pieces? It is so much more compacted then the one in my truck.
I like the simple gate valve design.
Bob
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As usual, l forgot to take pics of the most important parts…
Here are a couple.
This is the bushing and the axle that the membrane is screwed on (not shown)
I wuld say its a lot simpler thain yours. No levers, bearings, crews… l will make a fast drawing
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The valve does not close/seal 100%. I made the plunger loose to prevent siezeing. It doesent need to seal anyway, it is (shuld be) allways half open any way during operation. All it has to do is restrict the air flow enough for a perfect 50/50 mix.
I made the boddy of the valve by casting a 3/4" Tee full of aluminium and drilled out the cavitys. Its allso important to note l melted aluminium in my kichen wood stove while boiling down birch sap 
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OMG!!! There you go again, doing what others spend weeks on and you build it in a couple of nights. Casting your own Al valve is just amazing. 
TomC
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Wow, I just had to bookmark this one. Thanks for the drawing. And what Tom said.
Bob
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Kristijan! I’m looking forward to see what kind of lambda voltage you get when running the automixer.
Watch out, with everything automated you may get stuck at the farm with the kids while Karmen is out DOWing 
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I thought the automixer that Chris made moved double butterfly valves - one for air and one for gas. This one looks like it just is for air. I often wondered why just an air valve wouldn’t work. Can’t wait to see how this works as it looks like a simple way to go.
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Does all the air that the 2.3L engine breathes have to go through that small hole in the automixer casting? Seems a little restricted to me.
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Hi Don , Chris put a Ford 150 double throat throttle body ahead of the trucks throttle body. The two wood lines after the gas valves join together and become one two inch line. The gas goes into one side and air goes into the other side of the throttle body intakes . Just a head of the air side is a valve that is controlled by the auto air mixer. The ford throttle body is connect the trucks throttle body with a cable linkage so they open together and close. Two vaccum lines are connected just in front of each of the Ford throttle body intakes, the lines go to each side of the auto mixer canister with the plastic in between.
The Vacuum lines are disconnected in this picture. The filter is removed from the air valve so you can see the linkage connected to the valve and auto mixer canister. Just above the canister and to the right is the Ford throttle body.
Bob
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Thanks for the thumbs up guys.
JO, sounds like a blessing to me as much as l like DOWing, l am a first class “zapečkar” as is the term here. The translation wuld be something like “the one who doesent move from the house stove”. Being home on our small farm is better thain any caication to me.
Don, like Bob sayd, the automixer does only operate the the air valve.
Correct. Keep in mind l use a tiny gasifier. Its rather restrictive. Now l use a 1/2" ball valve for the air adjustment. Its open 100% and it gives me best power, when l start to lose power (and the O2 sensor starts showing lean) l close it a bit and know its time to shake the grate. That usualy happens arfter about 60miles of driving.
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Kristijan, I think the word for “zapeckar” in the US would be " couch potato". You certainly don’t present your self as a “couch potato”. TomC
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Or maybe closer to say “homebody”
I think couch potato is the urban adaptation, as they have nothing real to do at home, so park their butts in front of glowing screens… 
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What is the necessity of the “twin flaps” Ford throttle body? The way I see it is when they both open together you should be getting close to a 50/50 air/gas mixture right there providing the vacuum is equal on both sides which is the job of the diaphragm and air valve.
Kristijan, do you think your automixer will work without the “twin flaps”?
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the gasifier with coal seem to be easier to adjust (from the point of view of the ratio air / gas) than the gasifiers with the wood! Is this an impression?
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