Forge Chimney

[irnsrgn]

Venturi in use in a carbuerator is a long tapered cone that compresses the air being sucked in to it. then when it comes out the narrow tapered cone it expands mixing the raw gas intruduced into the stream of air for a more uniform mixture of the gas and air.

Venturi in an eductor works just the opposite, a long tapered cone narrows down to increase the pressure applied to it and when it expands into the pipe or tube it creates a vacum at abrupt terminus of the venturi and there is a narrow gap open to a hopper or a tube where the jet of compressed fluid or air expanding induces a vacum, you see this on fertilizer spray rigs for agriculture and its also the means of sucking from a container thru a small hose and the blending by the expansion process when firefighters educt foam concentrate into their fire hoses for fighting liquid fuel fires.

Jim C experimented with using a length of larger pipe at the top terminus of a
forge flue causing the heat and smoke from the flue to expand inside the larger pipe and thus creating a vacum to increase the draft (suction) at the bottom near the fire.

[Rick Barter]

I have a question for Uri. How hot does the square tubing get? I notice there's not much clearance between the tubing and the wall. I'm just curious because I'll be putting a chimney in very soon and would like to use this design.

[Hofi]

Hello Rick
It Is Not Very Hot On Regular Fire U Can Touch It With Your Hand,but If U''ll Make A Big Fire And In The Summre It Will Go Higher. In My Case I Went Through A Concreat Wall And There Is No Problam, But If U Go Through A Wooden Wall I''ll Sugesst U To Put Around The Tunel Any Insulating Matirial
To Be On The Safe Side.
Hofi

[Rick Barter]

Hi, Uri. Thanks for the information. I will be going through a metal wall. I think this will be fine. I may create some soft of insulation sleeve anyway, though. That way I can keep out the elements with some silicone caulk or something.

[Dave Leppo]

I don't have problem with solid matter going up the pipe, using a 12"dia horizontal and vertical pipe. The ash deposits in the horizontal pipe. I think a lot actually drops into the elbow. My horizontal pipe actually isn't horizontal; it slopes up slightly as it passes thru the wall. I scrape the ash out with a hoe occasionally, but it would take a while to impede the flow with ash, I don't us it every day.

BTW, at the forge intake point, I’ve formed the round pipe into a square, and attached it to a vertical plate, like a wall next to and over the fire pot.

This all draws pretty well, but I use a removable hood attached to this plate to try to get as much smoke as possible because my space is pretty confined. I also have an exhaust fan, which I use as needed.

[Rick Barter]

Goatman,

Any pictures? I definitely find them to be worth more than 1,000 words. :D