fume hood tryal

[callicom]

your not sidetracking anything here friend, as far as i`m concerned it`s all constructive and i apreciate all the input :mrgreen:
Well i`ve put the outer air shaft back on and it`s drawing fairly well from the two slots that i inted on matching up with two similar slots on the plexi hood. The only problem i see now is the wind, when there comes a little gust of wind it seem to counter the effect, i guess baffles or some kind of big protective exhaust protection would be needed, has anybody had this problem :?:

 

[eeTHr]

callicom---

I don't know if this will help with your configuration, or not, but there is a lengthy thread on venturis, with several people's different experiments and results.

I made some tests of different venturi designs, and posted the results, with diagrams, photos, and calculations, and came up with what I concluded was the best configuration and about how much suction can be achieved.

 

[callicom]

if this is the post with the pvc pipes i read it and i`ve been checking up on it, i`m applying the same principles as what i read on there, i apreciate your pointing it out to me anyway, thanks :mrgreen:

 

[callicom]

i`m a happy camper :!: after working all day it finaly works :mrgreen: i had entended the interior ventilating shaft and coned it to restric the air but it still didn;t work, the breeze from outside was neutralizing the vacuum when it was blowing. i have to admit i was a little discouraged and thought of giving up on this design, but i tried a step further and added a 4 feet extention on the outside of the barn with a foot extention on the wind side and it solved the problem. the Lord sure is good.
so here`s some pics of the final, i tested the hood without the front plexi since it`s not cut yet.

 

[jimdoc]

but i tried a step further and added a 4 feet extention on the outside of the barn with a foot extention on the wind side and it solved the problem.

Won't the wind change from day to day?

Jim

 

[butcher]

Nice.

 

[eeTHr]

I like the low and high suction ports. I hadn't thought of that until someone mentioned that the nitric fumes were heavier, and went to the bottom of the hood.



P.S. I just noticed that I forgot to put the actual URL into that link in my previous post. It's fixed.

 

[callicom]

but i tried a step further and added a 4 feet extention on the outside of the barn with a foot extention on the wind side and it solved the problem.

Won't the wind change from day to day?

Jim

it seems like the main problem was that before i put the extention on the outside the wind would hit at the crucial place where the vacuum effect was created, now you could see in one of the pics that its created safely inside the vent, i`m not sure about anything though, i have zero knowledge about this except from what i read in hokes and on some other post.
it should of been made to last though but since i was in the dark about the results and i was basicly experimenting i used uncoated plywood. i hope it will last until next summer so i can redo it better. i did spray rubber coating on the smaller venting shaft since i had a can laying around the house.
thanks for the link eethr i`ll go check it out.

 

[eeTHr]

calloicom---

I think a baffle, angled like the one Shyknee drew, in front of each of your suction slots would probably increase the suction. And since your duct is larger than your blower port, baffles of only an inch or inch and a half, shouldn't be any restriction on the overall blower flow. It would be worth a try, I think.

You could use a lighter or candle, and see how close to the suction slots you can bring it, before the suction puts it out. Then try the same thing after adding the baffles, to see how much difference it makes.

...Just a thought....

 

[callicom]

i went and checked the baffle design from skyknee, it doesn`t realy apply because what i`done is the same as your design where the hood tube actualy acts as a sort of baffle by extending itself further inside your bigger tube. the difference is that my tube or box from my blower is the one thats inside the big tube or box and it passes the lower slot in the hood by about a foot. you could see a pic with the outer box stripped off in the second batch of pics i posted.i based my stuff on you guys principles and the diagram i saw in hokes :mrgreen:
i`ll try a candle but the vacuum from the two large holes is not very concentrated and i dought it will put out a candle, it draws all the fumes though even without my front doors being instaled yet, i tested it by burning napkins in a tuna can and i watched the smoke curve right into the two slots

 

[seawolf]

I saw in one of the previous posts that wind direction was a concern. As an idea a turbine roof vent might be a help. No matter what direction the wind is coming from the vent will pull from the tube adding a few more CFM to the system, if it is dead calm the vent should not add much of a restriction. I have seen these in various sizes from 6" to 36" and some made of a plastic. If it is a metal vent coating it will be a must to prevent corrosion. As an added bonus closing in the end will prevent critters from getting in the tube.