Hi Krisitjan,
the safety filter commonly used in WW2 systems was a very fine mesh. If the main filter doesn’t work, the layer of dust on the fine mesh leads to a higher flow resistance and thus in a loss of power, so you notice it quite fast.
The mesh can be cleaned quite easy with a soft brush.
Gohin-Poulenc used white cotton wool. If there was some dust left in the gas, the colour changed from white to grey. So you can easily check if your main filter works.
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Here are some safety filters that come to mind: A 5" X 12 " piece of 400 mesh screen would give good protection. or A 25 micron pleated paper water filter cartridge with a sock over it would be fairly cheap ($4) and quick . or A sheet of 5/8 thick 65 PPI open cell foam oiled (UNI brand?).
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It seems l missnamed it. I want more like a ultrafine filter thain a safety filter. The thing is, there are trace amounts of soot geting by the towel filterand when the gas combines with air that has crankcase breather hose connected to it the soot and oil droets form a paste that might bake on the valves. I dont like that. Not a lot of this, but it adds up…
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Oh, I see.
Is that the reason for the delayed throttle response if hybriding?
If the gas is dry, how about a final filter with the filter cloth you used before?
Or, like Max often preferred it, a paper filter?
I would go for a dry filter like that. Best way to deal with fine particles.
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Well l thod the reason behind the hasitation is that the crankcase breather oil mist doesent lubricate the fuel injection meckhanism since its bypassed but now l am not sure…
Yes perhaps this will be the best. Now to find a suitible narrow carteidge… perhaps a vacuum cleaner filter?
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Apple wood makes a very nice flavor too.
Hi Kristijan, the heavy duty black plastic garbage bag is what Chris S. used when making the auto mixer that is in my truck. It is still good and operating fine, thousands of miles of use on the auto mixer. I can hardly wait to see the mixer working in your car. Would like to hear your comments on the difference in operation from manually mixing to automatically mixing the gas to air ratio. Also performance differences.
Bob
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Ultrafine filter: Have you ever seen the shadow mask material that is inside color television tubes and monitors? I wonder if that would have any application in our fire and smoke hobbies?
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How about some of those cheap face paper like respirators? I think I might try one in a quart glass jar for a small engine. Would need more than one for a large engine.
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Ray, what material are thwy made of?
Jeff, how wuld you connect them?
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I would try gluing them to a flat plate and make a simple manifold like box. I glass jar would be a problem because of drilling a hole into the glass, pooh.
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Thats why l lowe the grey sewer pipes you can see in all my builds. Making this filter houseing cost me 6 bucks and about half a hour to make two holes and connect it all. Plus it can be taken apart and its components reused.
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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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