questions about dual combustion fan Keystoker boilers

I have 2 draft gauges, 1 above the baro damper and one on the outlet of the boiler before baro damper. i use the little fan(axial) to keep the coal bed alive till the next call for heat. cycle timer is set for 3min every 15 min and just runs the stoker only. the 2 fan system is great in the summer time for my domestic water in conjunction with out door reset that runs boiler down to 135deg above 70 outside air. i set the baro damper to move the monometer just small amount upon startup of main combustion fan. that initial pressurization is what i set my draft for, just so it almost goes to 0 but stays negative. i keep a piece of 1/4 copper tube cut to length to test thru hole in access door if need be but during operation i have it set into the flue below baro for overfire draft. the axial fan will keep the coal bed red with almost no flames off of it, just a little air is all you need, not much. i have even toyed with idea of connecting some 4" sheetmetal pipe to the outside for outdoor air combustion (but it aint broke so i dont fix it). i have tried a speed controller on the combustion blower but it is shaded pole and doesn't take kindly to it, high and low air flow and it works great. Guy

Guy,

Do you see any different reading through the door vs between the flue outlet and baro? My gauge connects between the flue outlet and baro. I've never bothered to check through the door. I figured that since the boiler is open inside, it should read nearly the same as in the flue. With good coal, I set the baro at .02" with a good fire, and then set the combustion fan to give .01" or so.

It seems to me that your 2 stage setup should blow less heat up the flue when the boiler isn't running hard.

Fyi, I have a 4" line from outside, in which I have a small inline fan [think duct run booster]. It doesn't do much, just helps move a little air through the pipe. Fwiw, I don't think that connecting solid to the fan is a good idea. Differences in pressure in the boiler area vs outside and such. Maybe terminate right in front of the fan[s]. My 4" line just blows gently toward the fan at this time.

Thanks for the info.
Dave

Any other weirdo types here that are of similar thinking, here's a thread on variable feed rate options;

[not that you are a weirdo, Guy]

More babble -setup for variable stoker feed rate Keystoker

Dave

staybolt wrote:I have a k2 boiler and have the the small dayton axial fan attached to the inlet of the main combustion fan. had it on there for 6years now with no problems. i wired it to run ALL the time with main fan in the burner circut. I just attached fan with some rtv to the inlet of combustion fan and let dry. maybe will up load some pics. let me know. Guy

the axial fan will keep the coal bed red with almost no flames off of it, just a little air is all you need, not much.

Interesting idea, I would like to see a picture of it.

I hope you don't mind a couple questions to better understand your set up--

The combustion blower has an adjustable round plate on its inlet to regulate the volume of air supplied to the grate ---

Question 1 - With your axial fan setup, How open/closed do you have the blower inlet plate?

Question 2 - What setting do you use for the stoker? [i.e. turns in/out of the feed screw]

Question 3 - Upon a call for heat, How long does it take for the boiler water temperature to recover to its normal high temperature setting?

Question 4 - What is your flue gas temperature when the boiler is stoking at full fire? [and do you use an internal probe thermometer, or an external pipe thermometer]

Thanks

sorry for not getting back,
I run the combustion blower set up with no inlet regulator plate and set coal feed to max. I just so happens that the coal reaches the end of the drilled out portion of the sloping grate and is almost ash by then. when the boiler calls for heat the fire takes 2 min or so to be high fire and depending on how many zones are calling it may run short or long before it goes out on limit. Domestic water heater zone puts quite a load on boiler and when out door air temps are cold the boiler will run for a while. i used to have a flue temp guage but dont now. will take some pics soon. Guy

staybolt wrote:set coal feed to max.

At the "max" setting, the stroke is roughly one inch per minute;

staybolt wrote:cycle timer is set for 3min every 15 min

so in 45 minutes the timer alone would push 9 inches. Added to that would be an inch for every minute the aquastat is calling. Is that correct, or have I misunderstood something?

staybolt wrote:I just so happens that the coal reaches the end of the drilled out portion of the sloping grate and is almost ash by then.

Has the coal completely burned to ash by the time it reaches the end of the air holes? or is it "almost ash" but still some unburned coal?
Thanks

I understand the the k2 stoker assemblies are not all the same. I have the one they use on the stoves with nylon disk for the eccentric to move the push bar, i have also seen k2s with a wheel that rotates off the shaft of the stoker motor to make the eccentric. the latter can move alot of coal where as the one i have cannot. dont know what you have. what i try to do is to have a small amount of unburned coal at the end of the active portion of the grate during call for heat. i would rather have a small amount of almost burned up coal being thrown off than an inch or so of dead area on the grate blowing cold air into the combustion area. to me its like having a perpetual klinker. off cycle is different, just try to keep fire alive but not too much to overheat so an ash area will build until the next call for heat. with much trial end error i basically have a min and max setup both with coal and air, the axial fan running in off cycle can help greatly in slowing down the burn rate of the min coal feed setting and thus reduction on coal feed can be achieved for idle.

I'll try your method; Thank you for sharing so I/others can benefit from your experience and not have to do --

staybolt wrote:much trial end error