manometer question

 
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freetown fred
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Post by freetown fred » Sat. Dec. 05, 2020 9:05 pm

Yep, me too, that's why I asked you!!! LOL

 
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Sunny Boy
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Post by Sunny Boy » Sat. Dec. 05, 2020 10:19 pm

freetown fred wrote:
Sat. Dec. 05, 2020 8:33 pm
W, didn't J put them in an old mantel clock?????
Joe did that, yes. But he cut a block of wood to look like an old mantle clock. And it was dial type manometer gauge, about twice the price of the Dwyer red liquid sight-glass kits.

Paul

 
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Sunny Boy
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Hand Fed Coal Boiler: Anthracite Industrial, domestic hot water heater
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Coal Size/Type: Nuts !
Other Heating: Oil &electric plenum furnace

Post by Sunny Boy » Sat. Dec. 05, 2020 10:50 pm

You may remember back a few years when I did a test using two Dwyer red liquid manometers on my range. One where I have it now plumbed into the pipe about three feet up from the stove collar. The other temporarily sealed into a flue under one of the range's cooktop round covers, just before the exit collar.

Wasn't much difference in readings to be worth one spot is better than the other.

Part of what your readings will be is exhaust velocity past where the mano probe is located. If you read the Dwyer info, it can be used to measure exhaust velocity using both ports and both tubes.

When you place the probe into a large space it will read slightly lower because of the "plenum effect" that allows the exhaust to move more slowly in a lager space, verses having to speed up in a narrower space. And how the probe is facing and where it is in that exhaust stream makes a difference, also. If you've ever had to work on and modify engine carburetors and intake/exhaust systems, and you understand Bernoulli's and Venturi's work, you'll understand these effects.

Some of you may remember the tests a ran a few years back showing these comparisons.

So putting the mano in a pipe will tend to give slightly higher readings due to increased exhaust gas velocity past the probe tip, than if you install the probe in the stove body.

And exhaust gas turbulence is another factor to consider. Pipe bends, pipe walls, and MPDs cause changes in flow patterns that can cause false mano readings as they create turbulence that can have very different exhaust gas speeds. You want the probe in an area of pipe that is not near these turbulence-prone areas and the exhaust is going in a straighter flow. That's usually, at least 1-1/2 to 2 times the width of the pipe away from all bends and dampers.

Paul


 
KingCoal
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Post by KingCoal » Sun. Dec. 06, 2020 6:08 am

Since the in stove damper is the restrictor type that is open a fair bit and the decree that there be visible hoses and maybe not impressed with the look of the Mano much either ?

I think you have already expressed the best answer. Box up the Mano, resell it here ( or keep it as an investment toward your next stove ) and just run it.

Hitzer s are fine stoves built to do the job with minimal muss and fuss. If you have an IR thermo gun you can see the diff between the stove body and the pipe and if you think you’re giving up too heat just close the mpd alittle more

If I remember right ( don’t quote me ) I thought coal was to make stuff easier on you not just a new headache

 
Hoytman
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Post by Hoytman » Sun. Dec. 06, 2020 2:58 pm

KingCoal wrote:
Sat. Dec. 05, 2020 10:41 am
just to be sure, there is no negative pressure involved in any of this, except for the amount created by the venturi effect of wind crossing the top of your chimney.

what you are measuring with a properly placed mano tap is the amount of pressure at which higher density room air is being allowed to push lower density heated air thru and out of your stove and chimney.

"if it was any simpler, it wouldn't work" LOL
If I drilled the stove body what would define “properly placed”?

With the false back on this 354 a hole on the side or front of the stove might be best for inserting a bolt when the hole isn’t needed, but maybe a bolt would still work fine on the back.

In the context of your post that is somewhere above the fire. I did catch that part, but it also leads to something I noticed in another stove.

On Keystoker hand fed “Deep box” stoves there is a factory hole in the upper right hand corner of the ash pan door that I noticed in pictures. I can only assume this is for a place to take a manometer reading, but I cannot be sure. I did some poking around on their website and could not find any info clarifying what the hole is for. However, it seems I recall someone on this forum somewhere indicating that was the purpose of the hole. Maybe I should do a search here or maybe someone can verify it. If that is what the hole is for...

...I wonder why they chose to e ash pan door versus the pipe or above the fire bed? I have no clue. Just makes me wonder about drilling a hole at the rear air inlet on the side of the Hitzer, but I can see (best guess) the air velocity increasing at that location versus over the fire bed. Seems it would also increase in a pipe as well.

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