Draft Checks

KingCoal wrote: ↑

Thu. Feb. 15, 2018 7:38 pm

OK now we're getting some where.

READ the directions fill and zero the gauge properly and get back to us.

steve

Yup! like the saying goes, ...
"When all else fails, ... read the directions."

Paul

No no no no. You can not pinch the tube to zero the mano. By pinching you create positive pressure in the tube between the pinch point and the gauge. The tube must be freely open to the room to get proper zero.

These instruments are reading hundredths of an inch of water column pressure, which is hardly a fart in a hurricane. It is very sensitive. Putting your finger over the end (and pinching) traps air in the line creating various pressures within it as you move it around changing the tube's volume by changing the bends in it.

Edit - sorry, I blew up lol

i'll add a few comments about how and why this started in hopes of a better understanding of what i had found with MY stove and installation and wondered if the same style stoves were acting the same way a cross the board.

for about as long as i can remember there has been a theory ( that i have agreed with ) that more bends, and direction reversals in a smoke pipe will create added resistance to gas flow and thus reduce flue draft pressure in the system.

even MPD's and Baro's can be seen to reflect this by tapping Mano above and below them.

anyway that made me wonder about the added length and reversals involved in the gas path of true Base Burner stoves when operated in indirect ( base ) mode ?

when sampling from under the lowest damper in my smoke pipe ( during a mid cycle established fire with controls set for steady cruise ) i could read any level of Mano i set the dampers for and to set a baseline i set them for a -.04 reading.

because i knew i wanted to know what the reading would be in the CC i had already tapped a port in the stove wall above the fire pot and using the same tube removed from the smoke pipe went directly to the tap in the stove wall above the fire and found that in that position the reading was -.02

so i concluded that the internal passages created an additional resistance to flow of -.02 this i replicated at any set value in the smoke pipe down to -.02 at which i had a reading of .0 in the combustion chamber. i also established that if i left the CC reading at .0 long enough it would prove to be correct and i would set off the CO monitor.

a further point of interest to me was the fact that the closer i held the mano value in the CC to -.01 and used the primaries to control burn rate the higher the heat output of the stove and the lower the fuel consumption over 12 hr tending periods. proven by needing to turn down the primaries to maintain the 70* comfort level in the house.

there's more but i didn't intend to write a book here.

thanks,
steve

joeq wrote: ↑

Thu. Feb. 15, 2018 6:57 pm

Checking and setting zero Mike can be confusing too. If I pinch the tube to stop the flow to the gauge, it should drop to 0 right? But if I disconnect the hose, and release the hose, put my finger over the end or even place my finger over the supply port on the manometer, I get different readings. I guess I should read the directions on the proper method.
[/quote]

Hi joeq, if you suck fluid up a straw and then put your finger on the high end of the straw the fluid stays right? So you still have a vacuum...pinching the hose simply captures or "suspends" the vacuum. So both HI and Low ports need to be open to the relevant atmosphere in order to zero correctly.

I know, zeroing a gauge is as basic as 1,2,3. But because I hadn't run this Dwyers in a few years, I had to "relearn" it all over. So like "y-all" know, after I read the directions (again), zeroing is done by just disconnecting the supply line...which I did, and it "was" reading 0. And because it's late, (and don't want to bore you too much), with a healthy fire and full pot burning, I'll just say, both manos read W/I a tenth of each other, with the CC as Steve said, a tenth lower. But the manos will read basically the same in DD, and can only speculate that it's because the sensors are W/I 8" of each other. Once placed in BH, the CC will drop behind a tenth or 2. I did see one more interesting thing tho, when I was 1st checking comparisons tonite, in different modes, I noticed the CC would read quite a bit higher than the pipe, when I opened the ash pan door wide. Like I said, it's late, and I don't remember if it was in BH or DD, MPD open or shut, but when the ash pan door was opened up, the Dywers went up substantially. I'll have-ta re-check it tomorrow.
As of right now, the Olympics are done for me tonite, so I need to crash. See ya in the AM.
(Or PM, after work)

Joe, there is only one comparison that matters at present.

if the stove is in Base Heating mode when you walk in from work tonight,

BEFORE TOUCHING ANYTHING

check the 2 gauges and report the readings.

that's it, experiment done.

thanks,
steve

OK Steve, did it.
Came home to a pot temp. that still looked good, along with the fire. Natch. there was ash, and the clinker door was dark and grey, but not unusual after a 10 hr burn. The pipe mano registered -.01, and the CC was showing a whopping "0". I guess that would be considered a slow burn.
I went through my typical clean-out, and as I said before, nothing unusual. The CC follows the pipe but a tad less.
But I forgot to mention something else that was baffling. For some strange reason, even when I'm in DD, with the MPD wide open, if I open the load door, the CC draft reading drops to 0.

joeq wrote: ↑

Fri. Feb. 16, 2018 4:50 pm

But I forgot to mention something else that was baffling. For some strange reason, even when I'm in DD, with the MPD wide open, if I open the load door, the CC draft reading drops to 0

Yes, that makes sense to me..

That doesn't make sense to me. A "0" mano reading in the cc would allow flue gas to escape from the stove with the load door open. There has to be some draft there because I'm sure the flue gas is going up and out!

I don't know how to view inside the CC, with a draft. Would it be considered air flow(?), or a negative pressure? I would think the latter, because once the door is opened, the chamber is exposed to room pressure, and kind-a balances itself off. That's my take on why the CC draft goes away. If the draft was considered "air-flow", I would think the draft would increase with the open door.

yes if i have less than -.03 in the CC before i open the hopper cover my reading will go to .0 and if i wait long enough it will prove that is truly the case by setting off the CO detector.

because of this, even though i run as close to -.01 in the CC as possible all the time when it's time to tend and refill i open an MPD to bring the differential up so there's enough draft to pull any dust into the stove and keep fumes from getting out.

after i'm done i just set the CC back to -.01 and walk away, the Bi metal handles it from there.

tcalo wrote: ↑

Fri. Feb. 16, 2018 5:12 pm

That doesn't make sense to me. A "0" mano reading in the cc would allow flue gas to escape from the stove with the load door open. There has to be some draft there because I'm sure the flue gas is going up and out!

CC draft goes to zero because the open door makes the area directly above the coal ambient pressure.

You’re correct Tom, chimney will still draw and show a draft # because it’s hot, but because the area over the coal is of great volume the gasses slow dramatically (over the coals) due to the open door.

Same thing as opening the secondaries on a Holley.... for a moment there is no velocity...

Joe knows that! I’ve seen many large 4bbl’s stacked like cordwood in his garage

I tried to get a repeat performance of the phenomena that occurred the other day, when I opened the ash pan door, and the CC draft went up quite a bit. The stove is all settled in for the night, clean and hot, in BH mode, and I tried to duplicate it by opening the door with the MPD closed and open, and in DD, MPD closed and open, but tonite it wouldn't do it. Now let's see, where'ld I put them mushrooms?

OMG Joe please don't. there's no tellin what you might start seein and then we'll have to start all over again