Jump to content
I Forge Iron

Downdraft hoods.... ?


desmato

Recommended Posts

 Yes. You will create suction in the horizontal pipe if it is done right and the suction can be adjusted by moving the blower. The main idea is to keep the blower cool. Most blowers do not like hot gases. I have done it myself, using an old vacuum cleaner as blower, to get the smoke out horizontally, from a funnel above the fire. I did not like to take a hole in my roof. In my climate that is a continous source of irritation. In my case, the tee sits above the fire and the cleaner blows horizontally into the pipe but the idea is the same and my exhaust works great. Zero smoke in the shop if the vac is blowing..  

Link to comment
Share on other sites

I saw your video and was commenting in my 1st post about it.  I like your idea but I recall you saying somewhere about replacing the old vacuum motor for something a bit quieter or less bodged. I have to make 2- 90* bends to exit the wall, which I think may create too much restriction for your setup to work properly.  I want to do something similar but I also want to use the smallest diameter pipe possible through the wall. I need to go up into an attic area, then out the gable, hence the 2 - 90* bends in the pipe. 

My thoughts are:  10" horizontal pipe in the shop connected to the inlet/suction of the "blower" assembly and a 6" pipe exiting the blower and shop. Since it will create positive pressure, I should be able to go smaller in diameter on the outlet just as the leaf blower it came from works  The motor will not be in contact with the gasses or elevated temps, only the impeller and housing which are both very thick steel. (8mm for impeller and ~ 2mm for housing)

I have the 2- pillow block bearings, jack shaft + pulleys on order. I already have a 1/3 HP 1725 rpm motor, so.......  we'll see how it SUCKS in the next few weeks.

Link to comment
Share on other sites

If you direct the "jet" into a straight pipe it will work but if you feel OK with the fan being able to take the heat you will be well off with it. You mentioned cost and this becomes a question of balancing power consumption and investment. If you use a motor that runs too fast (the original one?) and you feel that you get too much draft you can strangle the pipe somewhere. It is counter-intuitive but the load on the motor actually decreases if you strangle. Look up centrifugal fan theory.   

Link to comment
Share on other sites

Yeah, I was struggling with finding the right rpm.  I have a 1740 RPM motor with a 1-1/2" pulley and ordered a 6-1/4" for the fan. I calculated it around 415 RPM (fuzzy math) which may still be a bit fast. Since this is a work in progress, I'm sure a bit of tweaking will be required. I'm also looking for a cheap variable speed motor control to fine tune it.

Link to comment
Share on other sites

  • 2 months later...

So here's an update.

I have the assembly all fab'd up, just need to grab a belt (hopefully can get by without a tensioner) and then see what kind of draft it has.

I used an old box fan motor which has 3 speeds, is brushless and reversible not that I will need that.  Once I finish the shakedown, I'll mount and plumb it in.

 photos show it upside down (I have a pulley for the motor and..... pay NO attention to the bedrail. it was free and fit the build)

     Todd

20170124_184656.jpg

20170124_184630.jpg

Link to comment
Share on other sites

  • 1 month later...
5 hours ago, PapaDooks said:

wish i could find a few of them bed rails. would sure save me buying angleiron for my forge table :D

I just got a full set of bed rails from someone who lives across the way from where my son has swim practice. I had spotted the pile of steel next to their garage a few days earlier, caught them as they were headed out one afternoon and asked them if they wanted me to get rid of it for them, and walked off with about thirty linear feet (+/- ten metres) of the stuff. You just have to keep your eyes open.

Of course, if you're grabbing stuff that people put out in the trash, you have to move as quickly as possible. I missed out on a beautiful metal-legged worktable that a neighbor was getting rid of because I had to go literally just around the corner to get my van. By the time I came back, someone else had already grabbed it.

Link to comment
Share on other sites

  • 2 weeks later...

The fan looks great.. Not sure if the motor will be up to the task if it was a box fan motor and had a blade attached to it.. It won't get much cooling without the air blowing over it, and with the added resistance of bearings from the shaft and such.. 

I had an industrial smoke remover made by Buffalo it had a squirrel cage blower mounted inside an enclosure with a TEFC motor.. Even said Dust proof and explosion proof on it.. 

Sadly it went to scrap with some other high value items before I had a chance to move all my equipment.. 

Link to comment
Share on other sites

Doesn't that use compressed air to induce a draft? Ah yes "Operates on compressed air or steam with operating pressures up to 140 psi."   I know of one air compressor that doesn't use a motor---a trompe---but does require a waterfall and some tunneling skills. (For a traditional one...)

So you can use an expensive compressor that wears out and is expensive to run and repair or just go buy a fan and have it blow into one straight leg of a T.

There are some forges designed to use compressed air to induce more air as a "blower" but they generally were used in major industry where a 1000 HP air compressor or steam boiler was common and so air wastage was so trivial that leaky pipes far exceeded it.

Link to comment
Share on other sites

  • 2 months later...

WOW.......  I can't believe how long it's been since I posted the last update.

Since then, I am on rev 3.0 which is also the final.  I was only using the box fan motor as a "proof of concept" to see if my idea made enough draft to go further and as I and others thought, it didn't have enough oomph to spin that impeller and bearings from a dead stop. It DID however, prove that it should work so now I have a 1/4 hp. standard A/C motor driving the system and it works GREAT !   I haven't plumbed it yet since I've been busy with everything else besides Forging, but I'll post a link to the youtube video below.

  Todd

https://www.youtube.com/watch?v=GYfeybH7M2w

  Now to finish the side blast build and connect this 'sucker' !

 

 

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...