DSM 1400 Secondary Inlet and Outlets

slinger100 wrote:That may be. It would be a matter of the air taking the path of least resistance. The baro being set to .03 I would think that as the grates get covered with more ash it would get easier to pull more air from the secondary air which is unblocked by any ash. When I purchased the stove I did think it was odd that the secondaries were not adjustable. But if the baro is set to a constant draft it should pull the same no matter what the bimetallic primary is doing. So I'm guessing that if the primary is wide open and the grates are clean most of the air comes from there. As the stove reaches it's set temp and the primary closes the manometer doesn't change so the air has to be coming through the secondaries more. Does that help or make it worse? Lol

thanks for the additional info about your experience and point of view, it will be helpful to many looking into this phenom.

i agree with your sense that the ash load plays a considerable part in this and "the path of least resistance" has yet to be fully reconciled in this topic.

i will add just one other observed point about my set up. you state that "as the stove reaches it's set temp. and the primary closes the mano. doesn't change so the air has to be coming thru the secondaries more "

i have 2 MPD's in my set up so I can set the draft and not have by pass bleed or wind impact the stove box quite as much. what I have seen is that if I open the primary I can watch the mano. register a drop in the in stove neg. pressure. as the stove heats up to the new setting and the intake flap begins to close the neg. pressure can be seen to rise back to it's original set point by the time the flap is closed to about 1/8" as before.

since I also HAD a Baro. I can verify that this won't be visible in that case because the baro. will cover it.

slinger100 wrote:As the stove reaches it's set temp and the primary closes the manometer doesn't change so the air has to be coming through the secondaries more. Does that help or make it worse? Lol

Makes things worse. After 5 to 6 hours my grates become plugged up enough that the stove temperature starts to drop off. By 10 to 12 hours the stove has dropped by 100 to 150 degrees. Doesn't help me any that the secondary inlet is reducing draft through the coal bed.

Where is your mano taking readings in realtion to your 2 mpd's?

rberq wrote:

slinger100 wrote:As the stove reaches it's set temp and the primary closes the manometer doesn't change so the air has to be coming through the secondaries more. Does that help or make it worse? Lol

Makes things worse. After 5 to 6 hours my grates become plugged up enough that the stove temperature starts to drop off. By 10 to 12 hours the stove has dropped by 100 to 150 degrees. Doesn't help me any that the secondary inlet is reducing draft through the coal bed.

i can not comprehend this, even of the 1300, having a smaller grate area. the hopper should have the gravitational flow force to keep pushing the ash directly under it into the ash pan.

the secondaries doing what ever they will, my 1400 will run with in 25* observed stove top temp. for 24-48 hrs. in other trials I have gotten more heat from a given bi metal setting with the secondaries blocked, but it comes at a cost of much lower burn times.

slinger100 wrote:Where is your mano taking readings in realtion to your 2 mpd's?

below both and at the top of the first 90* out of the exit collar.

Rberg, 5-6 hours is not very long at all. What kind of coal are you using? If it's pea you might want to try changing to nut so your grates don't get plugged so quickly. Do you have a manometer installed? It would be interesting to know what your draft is. It almost sounds like a low draft situation.

Kingcoal, I believe with the 2 mpd's you are cutting down your draft to the set point that you are comfortable with at steady burn. When you open your primary all the way that is letting enough air in to more equalize the air pressure thus lowering your mano reading. Like sucking a milkshake through a straw is harder than sucking water through the same straw. Its a matter of resistance

slinger100 wrote:Rberg, 5-6 hours is not very long at all. What kind of coal are you using? If it's pea you might want to try changing to nut so your grates don't get plugged so quickly. Do you have a manometer installed? It would be interesting to know what your draft is. It almost sounds like a low draft situation.

i agree, I had this issue to an extent when I was conducting low draft trials. the stove simply wouldn't make and hold heat out put.

my 1400 want's not less than -.04 WC to be happy, I also do my best to keep it from going over -.06 WC.

slinger100 wrote:Kingcoal, I believe with the 2 mpd's you are cutting down your draft to the set point that you are comfortable with at steady burn. When you open your primary all the way that is letting enough air in to more equalize the air pressure thus lowering your mano reading. Like sucking a milkshake through a straw is harder than sucking water through the same straw. Its a matter of resistance

yes, you are correct but, I have no other rate than "steady burn". other than when experimenting, which isn't often any more, I leave my MPD's alone, don't open the ash door when shaking down or refilling, and my stove doesn't yo-yo at all after a tending no matter how long the interval.

i am also not talking about opening the primary wide open, this would only drop my Mano. under -.03, and the secondaries would wash all the heat from the stove. been there done that wrote about it here.

when I want more heat I open the intake about 1/8" more than the present setting, this drops the mano. about -.005 WC and as the stove reaches the new setting and slows the intake the mano. reading is right back where it was. if I am not satisfied with that level of heat I repeat.

this practice keeps the secondaries under control and affords the fastest increase of heat and least loss of burn time.

King Coal, You see a drop in negative pressure when the manual pipe dampers are closed and you open the primary. This is what I was getting at when I said your combustion air openings (both primary and secondary) are beginning to exceed the volume that can pass by the dampers. In other words, the negative pressure in the fire box is beginning to get somewhat satisfied by the amount of air coming in because of the restriction in the pipe.

I'm still fighting with the weaker negative pressure causing more secondary air theory though. It goes against the "pressure dictates volume" rule so I'm not sure what's happening there lol.

yes, and I openly concede the point about the dampers and the intake.

i'm also willing to entertain the "rules" of equilibrium and pressure / volume.

thus the reason of sharing any of this to start with. "I" have nothing other than my observations to report, and AM baffled by them too but, not understanding what is seen doesn't erase what IS seen.

this stove/ hook up combination has been a real eye popping head scratcher from the begining, in multiple threads

like the issue of base heaters being able to produce more of a heat and combustion rate than in the coal fed them, i'm certainly not sure WHAT the answer is but I sure like the heat.

Before any of you go plugging things, perhaps a call to DS Machine is in order. The secondary air inlets were put there at a cost and for a reason.

lsayre wrote:Before any of you go plugging things, perhaps a call to DS Machine is in order. The secondary air inlets were put there at a cost and for a reason.

I agree that the secondary air was put there at a cost. They must have a reason for adding the extra cost. I'm going to give you my opinion / guess. My first guess is for wind gusts. During a gust, the air is drawn from the path of least resistance, which is the secondary air tube. By drawing from the secondary air tube, metered air continues to be drawn up through the grates. This makes for a steadier fire, as well as keeping heat in the stove. Kind of acts as a built in, non-adjustable barometer damper. During periods of no wind gusts, the air flows up evenly across the entire width of the glass, acting as an air wash for the glass. Actually, the air film flowing between the door, and fire bed would also help keep the extreme heat off the door & glass when the stove is really cranking. I've seen other stoves with bolt on door frames, where extreme heat warped the metal, creating gaps between the bolt on door frame, and stove body. Don't forget, D.S. Machine has some really high BTU ratings, as compared to other hand fired stoves. Also, over the fire air would help ignite volitles (spelling?). Is this extra cost of the secondary air needed? Probably NOT. The E Z-Flow Hitzer's are great stoves, and they don't have secondary air. However, D.S. Machine must see more pro's than con's to this secondary air. The only con I can see would be if the chimney has a weak draft.

oliver power wrote:By drawing from the secondary air tube, metered air continues to be drawn up through the grates.

I'm having a tough time with that theory.. It implies that the several little holes for secondary air are going to satisfy the pull from a 6 inch diameter pipe. I'd rather think that any negative pressure in the fire box is going to pull equally from any available opening no matter which one it is...

Lightning wrote:

oliver power wrote:By drawing from the secondary air tube, metered air continues to be drawn up through the grates.

I'm having a tough time with that theory.. It implies that the several little holes for secondary air are going to satisfy the pull from a 6 inch diameter pipe. I'd rather think that any negative pressure in the fire box is going to pull equally from any available opening no matter which one it is...

But the pressure drop experienced by the draft pulling through the established bed of coal and ash is significant, vs. a minimal pressure drop through the secondary (over the fire) air openings.