[TheForge] No More Smokin' Hoods

[Ron Childers]

We have a slightly smaller pipe (12") suspended on cables and counter
weights inside a larger pipe. We let it down close when starting the fire
and lift it up when it starts drawing. the stack is 3' higher than the
highest point on the roof. Works fine.... Ron C

-----Original Message-----
From: theforge-bounces at mailman.qth.net
[mailto:theforge-bounces at mailman.qth.net] On Behalf Of Andrew Vida
Sent: Tuesday, April 29, 2008 12:35 PM
To: Blacksmithing List Sponsored by ABANA
Subject: Re: [TheForge] No More Smokin' Hoods

I will note that the reason for this is because the sudden transition 
from open air to the stack is what causes the right pressure drop.  If 
you have a large hood that tapers to the stack opening, guess what: all 
that air is being corralled into the same place and no drop in pressure 
and therefore no flow...  Bernoulli 101. :)

You could probably get a little better performance if you replaced that 
8" flue with 10 or even 12.  It should suck mo' bettah.

Bruce Freeman had a very interesting contraption set up at his forge.  I 
will leave it to him to disclose or not, but I think the basic idea was 
really good.  Almost fabulous, but if I go that far I'll never see the 
end of his big head, and it's ugly enough at its current size.  No same 
person would want MORE of that.  No insane person would either, for that 
matter.

Trust me.

Peter Hirst wrote:
> Had an AHA! moment in the shop  today.  Since I got the forge up and
running over the winter, my special custom-designed open hood has failed
miserably.  It covers the entire area of the forge (2x2) and is only about
18" above the fire.  It tapers beautifully to an 8" adapter and is topped by
12 feet of 8" pipe with no cap.  Works beautifully on paper.  In the shop,
hardly at all.  Some smoke stays under the hood, and some even goes up the
stack, but mostly it just billows and swirls and spills out, even when the
pipe itself seems to be  drawing well.     I have noticed several times that
at the joint where the hood meets the pipe, it draws like crazy, and even
with a  roar when anything flaming is placed near that spot.  Even then,
smoke is going the wrong way at the edge of the hood. A lot of air goes up
that pipe, but it doesn't take much smoke with it. SO today, when I couldnt
stand it any more, out of sheer desperation I took a spare 4' section of 8"
pipe and inserted
 it up under the hood at the joint into the existing 8".  That put the lower
end, with about a 30 degree angle at the opening, just a couple inches over
the fire..  As soon as I connected it, I had a winner.  The fire literally
roared into the 8" opening, sucking smoke from at least a 12" radius around
it. It may just have been because I was paying closer attention, but the
fire seemed to burn hotter, cleaner, and more efficiently.  Things were
suddenly so much better that just for grins, I got a nice clean, hot, deep
open coke fire going and dumped a few fat shovels full of green coal  on it.
No problemo.  All that thick, sickly yellow smoke -- and I mean all of it --
disappeared like a wisp into the stack.  
> 
> So now my entire hood and vent system consists of just 16 feet of 8" pipe
with  a 30 degree bevel at the bottom.  No side draft, no hood, no expansion
chamber, smoke shelf, step down, step up, 12 " flue,  nothing.  Just 16 feet
of pipe.   It doesn't interfere visually (in fact I can see the work better
than with smoke escaping from under the hood) or mechanically with the fire
or the work,  and if it ever does need it for a particular piece, I can
either swing it a few inches in any direction or remove it temporarily and
rely on the hood.  I was on the verge of ripping out the whole thing and
building a side draft with a 12 inch flue from scratch,  and investing in
about 12 or 16 feet more of 12" duct for the portable rig for shows.  Now
I'm all set with the shop, and for the portable rig,  think I'll just go
with the 8" pipe set about 4" over the fire, just like the shop, or maybe
resting right on the hearth with the end cut at 45 degrees.  .
> 
> Life just got a whole lot simpler.
> 
> Keziah
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	-Andy V.

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