Draft Checks

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Sunny Boy
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Post By: Sunny Boy » Sun. Feb. 18, 2018 9:59 am

FWIW. Just did the ash drawer mano test on my #6 while it's in BB mode, with an added twist.

Without changing the primary damper settings from normal heating position, the mano is reading just over .03 in the pipe before the thimble.

I put the mano probe in about 6 inches through one of the six wedge shaped primary damper openings. The reading was stable and just below .01.

I then held the tip of the probe in the damper opening, where the air velocity would be faster. It read just slightly over .01.

While that doesn't seem like much, the probe tip was right at the junction of the higher room pressure, that would give a reading zero pressure difference ,and the ash drawer that gave a slightly less pressure drop reading than right at the opening. So why between those two points of higher pressure readings is the mano showing even less pressure ? It's because of what Scott said, that an increase in velocity causes a decrease in pressure. ;)

Paul

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Lightning
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Post By: Lightning » Sun. Feb. 18, 2018 10:32 am

Nice, so from your observations the decrease in pressure at the "nozzle" where pressure is traded for kinetic energy, how much was the drop? About 3 thousandths of an inch of wc?

I was just about to start looking up equations but measurements are easier lol.

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Post By: Sunny Boy » Sun. Feb. 18, 2018 10:51 am

About .005 less pressure at the damper opening than in the ash drawer area.

Paul

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joeq
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Post By: joeq » Sun. Feb. 18, 2018 11:10 am

My question still stands. Does thousandths of an inch matter in our stove performance, if these reading are even accurate? If the probe were inserted at different locations around the grates, or grate chamber, would they repeat, or give exact same readings? I would think they would differ if placed at a section of the coal bed that was burning W/O restriction of ash, as compared to another area that was clogged down.
I think Scott was right, in that these readings aren't beneficial to the user, but maybe to the stove designer on the quest for the perfect stove. I could see that if certain readings showed us the best placement of primary to MPD settings or adjustments, that would allow an "optimum" burn, but think that with so many variables involved, these readings internally never remain constant. All in all it was interesting to observe some of these results, but I don't see a need to continue checking. Unless some-one can convince me differently. ;)

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Post By: freetown fred » Sun. Feb. 18, 2018 11:53 am

OK, after reading all this many times, I'll try---Oh hell, no I won't--I'm with you J. :)

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Lightning
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Post By: Lightning » Sun. Feb. 18, 2018 12:01 pm

I agree Joe, it's just interesting to see the measurements and what they imply. I ran down stairs and did a few of my own this morning. These are with a low-medium fire that has ashed up a bit. Last tending was 18 hours ago with sorted stove size coal.

Noteworthy points about these readings are the pressure drop at the lip of the primary air opening and the slightly stronger negative pressure under the grate as compared to above the fire which is more dramatic with a fresh and hotter burning fire.
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joeq
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Post By: joeq » Sun. Feb. 18, 2018 1:23 pm

Pretty impressive Lee. Those readings are quite a bit higher than mine were. You have a real fire breathing dragon there. :yes:
(I also like your reference tapes in your photos. Classy)

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Post By: Sunny Boy » Sun. Feb. 18, 2018 3:46 pm

Yes, to the average stove owner a mano is only good for resetting the dampers once the owner has established what the best running position is.

I find I rarely use the mano with the #6 because once the dampers are reset that's it, no more need of adjustment until the next reload and ash shaking.

But with the range, we are changing damper settings alot during the day to adjust the temps to whatever cooking, baking, or just room heating needs are then. So the mano gets used each time to know if the damper settings (there are 6 dampers on my range) will give the required draft to reach the temp needed based on the outside air temps, which as we know, also has an effect draft. I find that I could do without the mano for the #6, but not for the range.

Beyond that, it's just to those interested that these other numbers show some of how the stoves work and how different size stove firebeds, such as Joe's, verses mine, verse Lee's, can have such different levels of draft when comparing the same areas. I think that was part of Steve's original intent for asking. And as a fellow stove tinkerer, I think it was an interesting topic. ;)

Paul

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Post By: joeq » Sun. Feb. 18, 2018 4:16 pm

Hey Paul, if your range is that sensitive to draft settings, do you think there might be a benefit to using some sensing "inside" the stove somewhere too, along with your pipe sensor? Or have you got it pretty well mastered, it's not really needed.

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Post By: Lightning » Sun. Feb. 18, 2018 4:35 pm

joeq wrote:
Sun. Feb. 18, 2018 1:23 pm
Pretty impressive Lee. Those readings are quite a bit higher than mine were. You have a real fire breathing dragon there. :yes:
(I also like your reference tapes in your photos. Classy)
Hey thanks partner! She keeps us warm, that's what's important. ;) and saving big money on the heating bill. With the time and effort involved with this hunk of scrap metal I've earned every dollar of it :lol:

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Sunny Boy
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Post By: Sunny Boy » Sun. Feb. 18, 2018 7:03 pm

joeq wrote:
Sun. Feb. 18, 2018 4:16 pm
Hey Paul, if your range is that sensitive to draft settings, do you think there might be a benefit to using some sensing "inside" the stove somewhere too, along with your pipe sensor? Or have you got it pretty well mastered, it's not really needed.
Let me clarify, Joe. The range is more sensitive because of it's designed shallower firebox, but only because our use of it needs it to be more sensitive to our variations in cooking temperature needs over the course of a day. When I just use it as a heating stove it's, "set and forget".

Just like using an exhaust gas analyzer to tune an engine, the mano readings in the pipe tell me all I need to know. ;)

Paul

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Post By: joeq » Sun. Feb. 18, 2018 7:12 pm

That's what I was talking about Paul. Because you use your stove for cooking, and accurate temperatures are important, would interior draft readings help in tuning it better, for those temps? Or do you and the Mrs. have it all under control, that no more data is required to accomplish your cooking needs?

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Sunny Boy
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Location: Central NY

Post By: Sunny Boy » Mon. Feb. 19, 2018 7:32 am

joeq wrote:
Sun. Feb. 18, 2018 7:12 pm
That's what I was talking about Paul. Because you use your stove for cooking, and accurate temperatures are important, would interior draft readings help in tuning it better, for those temps? Or do you and the Mrs. have it all under control, that no more data is required to accomplish your cooking needs?
You would think so, but it's not practical to have mano readings from inside the range because of the design of the range.

If I took readings at the primary they would be much lower readings that use less of the mano's scale range. Any changes to damper settings would not be as easy to see what bigger changes those primary adjustments make after the air has greatly expanded and sped up after it was converted into hot exhaust.

If I took readings downstream of the firebox, the velocity and pressure drops are still quite low because the flue cross section is quite large, so again the reading variosions would be slight and tougher to see.

Readings taken further downstream in the narrower flue pathways, would need another mano because the exhaust path sometimes gets changed as we heat different parts of the range more than others. That just makes it more complicated to remember which flue pathway reads what and when.

But, whatever we do with the primaries, and the flues, it all goes out the pipe so that makes one place to get readings of everything going on in the range. Plus, because the exhaust has more velocity and pressure drop there, that shows up as a greater variation in the readings when we make small changes in dampers. And that greater variation makes it much easier to see small differences in damper settings when making changes in heat output. ;)

Paul

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Post By: joeq » Mon. Feb. 19, 2018 4:22 pm

Makes sense to me Master Paul. Thanks for the "brief", but thorough synopsis. :yes:

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