# Fume hood venturi.



## glondor

Hey all I need the assistance of the fume hood experts. Every attempt to vent with the venturi effect has failed. I have increased the size of the blower 3 times thinking I was not moving enough air. ( thanks to Craig the furnace guy in Hamilton). In each case I get a slight positive pressure at the hood inlets instead of a vacuum. The pipes increase in size from 3 inch to 4 inch to 6 inch as they leave the building. Air flow is strong. I get no draw in the hood, just a slight positive pressure. Can any one give me some help? I will answer any questions regarding this.


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## Barren Realms 007

Your should have your blower attached at the straight part of the "Y" and you will have less air turbulance.

The fan and blower you are using will move 2,000 CFM or more, way more air than you need.


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## glondor

I will try to rework it. Thanks BR. My hood is large. Dual hood, Two intakes in left side and one intake in right. Need to move a lot of air.


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## Barren Realms 007

Your main restriction will be in the size of your vent pipe.


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## goldenchild

I don't know if I'm missing something here but... your blower is on the wrong side. In the third picture it should be blowing from right to left and then up through the ceiling. Also it looks like your piping is all the same width. At the hole above the fume hood there should be constriction to create the venturi affect.


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## glondor

I had it that way in the beginning Golden child. It did not draw either. Small blower top left, now blocked and reworked to top right.


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## goldenchild

Well. I'm pretty sure it definately won't work with the blower on the exhaust side. The small blower may possibley not be enough? There are possible leaks in the setup? Did you test just putting the blower on one section of the pipe with the constrictive piece and seeing if it drew? You gotta do this piecemeal.

Edit I didn't even see the second pic. It looks like your piping is too wide at the down pipes. To make it easier I bet you used Ts that matched the pipe widths. 3 inch? It would probably work better if you had reducers at each side of the piping with a 1-1.25 quarter Ts in between to create the venturi affect. Also you will probably need some kind of fixture to close the hood or have one hell of a blower!


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## glondor

Thanks for your help Golden Child. I gave up on the small blower blowing across the intakes in favour of the larger one drawing from them because I thought the small one was too small. I was hoping the way I have it now would work. I will re arrange the Y pipe at the blower to blow straight through as per Barren realms suggestion and also go to a larger pipe just after the Y and see if that works. 

Any other suggestions welcomed. I need the damned thing to work.


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## goldenchild

glondor said:


> Thanks for your help Golden Child. I gave up on the small blower blowing across the intakes in favour of the larger one drawing from them because I thought the small one was too small. I was hoping the way I have it now would work. I will re arrange the Y pipe at the blower to blow straight through as per Barren realms suggestion and also go to a larger pipe just after the Y and see if that works.
> 
> Any other suggestions welcomed. I need the damned thing to work.



Just keep it simple. Give me a sec to draw something up.


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## jimdoc

Page 71 of Ammen's book shows a fume hood venturi setup.

Jim


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## goldenchild

jimdoc said:


> Page 71 of Ammen's book shows a fume hood venturi setup.
> 
> Jim



Dang lol.


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## rusty

goldenchild said:


> jimdoc said:
> 
> 
> 
> Page 71 of Ammen's book shows a fume hood venturi setup.
> 
> Jim
> 
> 
> 
> 
> Dang lol.
Click to expand...


Print version


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## samuel-a

jimdoc said:


> Page 71 of Ammen's book shows a fume hood venturi setup.
> 
> Jim



Yup, that's prcatically what i built here


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## glondor

I did base my first attempt on a super drawing by 4metals in a "build your own fume hood thread" Here>> http://www.goldrefiningforum.com/phpBB3/viewtopic.php?f=40&t=4776&hilit=hood+vent Nice drawing with multiple intakes. I also referenced your photo Samuel A. I will work on it tomorrow. Maybe later tonight. I will try to rearrange the pipes.

Thanks for all your help. I will keep you posted.


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## glondor

Ok I did a straight through run of the 4 inch, using a sanitary t at the junction with the 3 inch pipe in the hood. No joy. Blows out all 3 vents really really good. I guess I have to rearrange the pipes again to the other side of the hood and try blowing across the interior vents.


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## goldenchild

Again. The blower is on the wrong side. The only suction you MAY achieve is right at the joint. The fan has to go on the other side.


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## Barren Realms 007

Take the Tee out and put the Wye back in. Also try taking some cardboard and tape and close up one side of your blower.


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## goldenchild

Barren Realms 007 said:


> Take the Tee out and put the Wye back in. Also try taking some cardboard and tape and close up one side of your blower.



I don't get it. Unless he puts a jet engine on the exhaust side there won't be enough suction at the down pipes.


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## glondor

SOOOOO, all I need is a jet engine,,hmmm That I could probably do....

Goldenchild. Are you sure it will work? I took this design from something 4metals drew up in another thread and if I recall he has built many fume hoods.... Not doubting you brother, just getting tired of reinventing this thing.









how to build an acid resistant hood & scrubber


Building an acid resistant hood. A good sturdy acid resistant hood is the backbone of any refining and or assaying lab. They do get expensive if you buy them from a scientific supply house. To build one yourself you need to use 3/4" plywood and build the equivalent of a doghouse with a 4 foot...




goldrefiningforum.com


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## eeTHr

I'm planning to build a venturi system also, so I've been following these posts whenever I see them.

The first suggestion someone posted on this was to have the "downpipe" (from the hood going up to the exhaust), smaller than the exhaust duct, to product more air pressure and prevent the flow from starting off going into the hood, thus producing some suction out of the hood, which would continue in that direction once started. This sounds logical.

Next, came the suggestion of the exhaust duct narrowing down at the "T" to the hood, accompanied by a drawing. The drawing had the same size small pipe from the hood going into the "T." This narrow section of the exhaust ducting would increase the speed of the air through the "T," and seems like it would produce more suction effect.

I had a hard time getting my mind around the "blower on the wrong side" part, which someone mentioned, but now I see that since the blown air passes over each "T," it puts them all in series, with the same air speed over each one. Whereas having all the hood pipes joining, before getting to the venturi "T," places the hood pipes all in _*parallel,*_ and will _*divide*_ the air speed by the number of hood pipes.

As a knee-jerk reaction, I like the design pictured in the book best. Because it just _*looks*_ like it would draw more. But looks don't necessarily count, I guess.

One interesting thing I know---my brother made a suction pump with a water hose, just coming out of a faucet, and pumped the _*air*_ out of his car air conditioner with it. It was a venturi set-up, and simply used a "T" connector. If I remember correctly, the air line was, in fact, smaller than the water line, at the "T" connector.

I was planning on seeing if I could get a "Y" PVC connector, with the angled branch for the hood ducting, smaller than the straight branch. And if that didn't pan out, I was thinking of using a 90 degree fitting, and drilling a hold at the elbow, so a smaller pipe from the blower would insert and go a few inches up the exhaust end for a suction design similar to the book picture.

I hope this discussion continues, because it would be helpful to many, if less expensive blowers can be used because the fumes wouldn't go through them.

I'm not ready to start my project yet, or I would post some vacuum readings from the different configurations.

Thanks to you guys for posting what you have so far!


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## goldenchild

glondor said:


> SOOOOO, all I need is a jet engine,,hmmm That I could probably do....
> 
> Goldenchild. Are you sure it will work? I took this design from something 4metals drew up in another thread and if I recall he has built many fume hoods.... Not doubting you brother, just getting tired of reinventing this thing.
> 
> http://www.goldrefiningforum.com/phpBB3/viewtopic.php?f=40&t=4776&hilit=fume+hood



At the least your current configuration isn't working  I am currently working on mine and may take some pictures later in the day. I'm in the testing phases right now. I can say that with the configuration above I am getting results. There are leaks and nothing is sealed but there is still suction so I'm sure it will work when all is in place. Like I mentioned you should do this piecemeal making sure one piece works before moving onto the next and making nothing permanent until the end. Hence the leaks. My set up is much smaller only having one downpipe but the principle is the same. I think your blower is more than enough to accommodate all of your downpipes.

Edit Keep in mind that with 4metals' design the fumes are being drawn in and exhausted directly through the blowers.


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## eeTHr

goldenchild---

I made a fume hood out of a plastic tub somewhat like the one in your picture. It seems to work pretty good for awhile, but it turned out that the heat made the plastic brittle.

One day, when I wasn't using it, my cat jumped on top of it, and the whole top shattered and fell in.

Have you ever seen a cat run really fast? :mrgreen: 


Maybe yours is a different kind. :?:


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## goldenchild

Was yours made of #2 (HDPE), #4 (LDPE) or #5 (PP) plastic?


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## eeTHr

I don't know. I got it at Lowe's. It was just one of those rubbery kind of translucent tubs, with a top that clamped-on at the handles. It's for storing stuff, I guess. It was somewhat flexible, and seemed to hold up to acids well.


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## goldenchild

Ok so here is the configuration I decided on. I took this picture right before sealing everything. Obviously the blower hasn't been set up and any suggestions on what to use to hold up an odd shaped object like this would be appreciated :roll: I also have not joined the two 90 degree elbows yet. I'm thinking of joining them together with a union or something similar. This way if I have to move anything for maintenance and what not I can detach the hood from the exhaust pipe. Anyone see any downside to that? After that I guess the next step will be to film the fume hood in action 8)


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## Barren Realms 007

You can get a couple of flanges with a gasket between them that will last longer and give you less trouble than a union and will possibly cost you less.


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## eeTHr

Every time you add a 90, it adds a restriction factor to your flow.
You can use a 45, and twist it 45, to reach the wall. Run that directly through the wall, and put the second 45 outside, and twist it to go up the outside wall (I assume that's where the existing goes, to above your roof).

This would reduce the total bends from 4 x 90 = 360, to 2 x 45 = 90 degrees. This would reduce back pressure from your exhaust line, and increase overall suction.


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## Barren Realms 007

eeTHr said:


> Every time you add a 90, it adds a restriction factor to your flow.
> You can use a 45, and twist it 45, to reach the wall. Run that directly through the wall, and put the second 45 outside, and twist it to go up the outside wall (I assume that's where the existing goes, to above your roof).
> 
> This would reduce the total bends from 4 x 90 = 360, to 2 x 45 = 90 degrees. This would reduce back pressure from your exhaust line, and increase overall suction.



Under normal circumstnces this would be true. But with him reducing down to 2" at his processing container and then expanding back up to 4" after he leaves this it will not make that much of a difference because his restriction will be at the 2".


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## eeTHr

I think the smaller PVC at the "T" would have a higher flow rate within it, and also put some load on the motor, thus reducing total air volume. When the air exits the "T" restriction, it will spread out and slow down, and there will be less flow volume, but only proportional to the power limitation of the blower motor causing it to slow down.

In other words, if the motor didn't bog down at all, there would merely be a trade of medium air speed for high speed at the smaller diameter "T." Then a trade of high speed for medium speed after the "T." But since the restriction will cause the blower motor to slow _*some*_ amount, yes, there will be reduced air flow overall.

Kind of like when a electrical transformer raises the voltage, but lowers the current, with the power remaining the same, except for losses due to less than 100% efficiency of all transformers.

But I also think that adding futther resistance to the exhaust, of a type which has no trade-off but is pure flow reduction, would be non-optimum.

The difference between 360 degrees and 90 seems significant. I know there are formulas for this when running water pipes, and similarly for designing air conditioning systems.

A good way to determine the amount of suction gained, by eliminating 270 degrees of turn, would be to measure both configurations with a vacuum guage at the hood pipe.


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## Barren Realms 007

All of those are good point's eeTHr. If I were close I would take my air velocity meter and see what the readings are under the different circumstances, but I'm not. Let's see how he does when he cranks that baby up. 8) 

All the point's we both have laid out might be mute because it is such a short run they will not come into play. 

One thing I would recomend is him putting a drain port on the pipe to drain any condensation he gets downstream of the hood.


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## eeTHr

It might be good to tip the horizontal piping a little down grade on the exhaust end, so the condensation doesn't flow back down into the hood at the wrong time.

And, as you said, put a 1/2" PVC ball valve at the lowest point. This would require drilling and PVC primer and glue, but that's pretty easy.

The short distance of the exhaust run, won't reduce the negative effects of the 360 degrees worth of turns. There is even a drag factor per foot of _*straight*_ pipe, which must be calculated per building codes for water pipes. I'm not familiar with the codes for air ducts, but there is no reason not to believe that there is some significant drag factor in the straight sections there, also.


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## callicom

jimdoc said:


> Page 71 of Ammen's book shows a fume hood venturi setup.
> 
> Jim


this hood looks like the blower is pushing in a smaller pipe thats inserted inside the bigger pipe causing a siphonning effect, is that right :?:


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## glondor

I tried this with my set up, it did not work for me. 3 inch inside 4 inch passing the T. No draw at the hood.


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## Barren Realms 007

glondor said:


> I tried this with my set up, it did not work for me. 3 inch inside 4 inch passing the T. No draw at the hood.



I wonder if it would work with a 2" pipe inserted.


I have never done it but my dad use to tell me a story of a room where the air was being sucked out of a room rather than being blown into a room. When investigated the problem he found that someone had installed the Wye backwards in the duct run.

I still think you are trying to move too much air thru the pipe from that blower. 

Ask your friend that gave you the blower if he has an old bathroom vent fan (they put out 100-150 CFM) and set it up to blow into the pipe. If he dosen't I can send you one I have the gut's to probably 50 of them in my shop and I'll be glad to send one to you.

Try a hand held hair dryer taped in there.


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## eeTHr

Someone suggested an electric leaf blower, I think on the other thread about hoods. They do put out some good CFMs. They are loud, though, so I'm thinking of sound proofing around it, with an opening for the air intake.

It was also mentioned somewhere that it should be 100 CFM per square foot of opening in the front, in order to have sufficient suction when working with the door open.


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## eeTHr

I just took a quick look at Lowe's for leaf blowers, to check approximate prices and CFM. Here's a 12 Amp Black & Decker for $50 plus tax.

It says 245 CFM (at 200 MPH). That would pull an opening of 20" w x 16" H, for a dual hot plate setup, or 18" x 18" for a single.

But that's not counting efficiency loss due to the venturi effect. Does anyone know the maximum effeciency for the venturi, and the best configuration for achieving that?

Edit: They also have one made by Task Force, for the same price, rated at 380 CFM.


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## goldenchild

P.S. A 100-150 cfm fan/ hair dryer/ leaf blower won't be enough for glondor's huge hood. Not even close.


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## 4metals

When you open the door were you able to smell the ongoing reaction?


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## goldenchild

4metals said:


> When you open the door were you able to smell the ongoing reaction?




No. In fact, the video only shows when the reaction was very tame. I got a little over excited and added too much nitric almost causing a boil over. A bunch of NOx gas got produced but was still all good. Even when open. This design really sucks :lol:


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## eeTHr

goldenchile---

Thanks for making a video!

But now I'm wondering why the sides of the hood tub didn't pull inward when you closed the door, since I didn't see any air inlet holes in the hood.

Does the reduced air flow, in turn, reduce the venturi effect? Maybe the venturi system is self-compensating in that respect? If that is so, it would be another interesting benefit of the venturi system.

When I had my plastic tub hood, I set it on it's side, and used the lid as the front door, with side hinges. I only had a small suction fan at first, but when the door was about an inch from being closed, the suction would close it the rest of the way. It wasn't enough suction to use it with the door open, but I had to drill some air vent holes to get a flow of air through the hood and thus out the exhaust duct.

When I changed to a shop vac, it had more suction, and I had to drill more holes, or the sides would start pulling in.

It seems like you would need at least a few air inlet holes, in order for the fumes to flow out of the hood, though. (But I didn't see any buildup of fumes in the video.)

Glad to see it working, whatever is going on with it!


P.S. I looked back to see if you posted the rated CFM for that blower, but couldn't find it. What is the blower's CFM?


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## goldenchild

The hatch to this hood doesn't lay perfectly flat. There are a few millimeters of space on the bottom and on the sides to about the half way mark. That’s where the air is coming in from. 

I've already started working on a more traditional design though. I was doing some AR reactions today and caught a few whiffs. I guess since AR fumes are heavier that just NOx and the reaction was much more aggressive, the fume hood almost couldn't keep up. The solution would be a bigger blower to create more suction. But as it is, the blower is more than needed if used traditionally for this tiny hood. It's 465 cfm.


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## eeTHr

Hmm. That's even more than the leaf blower (with an air speed of over 200 MPH)!


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## eeTHr

Well, I got curious about the venturi design, and the possible amount of flow through the air inlet (pipe to the hood), as a percentage of the CFM from the blower. So I did some searching on the Internet.

The basic venturi has no air suction inlet, but merely produces a high velocity, low pressure area in the restricted portion (throat) of the device.

It looks like most of the designs for suction type venturis are for the purpose of merely creating a vacuum, rather than producing a significant _*flow*_ volume.

Surely there must be a configuration to maximize the _*flow.*_


Here is one used to produce vacuum to operate aircraft gyros. It produces enough flow to spin a rotor, powering the gyro---

Nine Inch Suction Venturi

Here is shown design characteristics for suction venturis, but it's based on liquid or gas being forced through the device, thus sucking air into the output flow---

Modeling of Suction Venturi Flows

Below is shown the innards of an air-air model, but again, it seems to be for vacuum rather than flow---

Venturi Vacuum Generators

Here is a multi-stage air-air suction venturi, again emphasis is placed on vacuum creation---

Air Powered Vacuum Pump

There are even several types of venturi scrubber systems, which could prove to be interesting---

Venturi Scrubber


I think the data is somewhere in the above, to enable the design of a configuration for maximization of *flow* using suction venturis. But what the maximum percentage of blower CFM obtainable is, I don't know.


Below shows differing designs for the air inlet nozzle, and although it is for water-air devices, it may be somehow applicable. It also mentions adjusting the nozzle depth to alter the suction (and thus flow rate?) of the air.

Basic Venturi Construction for the DIY Crowd


The question is, "Does the venturi system offer benifits over the direct suction method, which requires a chemical resistant blower?"


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## goldenchild

eeTHr said:


> The basic venturi has no air suction inlet, but merely produces a high velocity, low pressure area in the restricted portion (throat) of the device.



This makes perfect sense as to why the fast rising NOx fumes were easily exhausted but not the heavier AR fumes. Also the insense smoke when testing.



eeTHr said:


> The question is, "Does the venturi system offer benifits over the direct suction method, which requires a chemical resistant blower?"



Besides not having to buy a very expensive chemical resistant blower, I would say no. I still have a trick or 2 up my sleeve to get around this but if it doesn't work I may have to break down and buy one of these distressfully expensive units


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## eeTHr

goldenchild---

I was thinking about the picture of the multi-stage air-air suction venturi that was in one of the links I posted. And it reminded me of the diagram you posted, with the multiple suction ports.

I wonder what would be the effect of having the same setup, but all of those ports suck from the *same* hood?


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## goldenchild

eeTHr said:


> goldenchild---
> 
> I was thinking about the picture of the multi-stage air-air suction venturi that was in one of the links I posted. And it reminded me of the diagram you posted, with the multiple suction ports.
> 
> I wonder what would be the effect of having the same setup, but all of those ports suck from the *same* hood?



That's actually what I was going for in the picture. I made the picture for glondor's hood. I figured it would work somewhat like mine. I think a downfall of having multiple ports would be weakening suction the further away you got from the blower. Or maybe not. I don't know.

Sooo. I modified my fume hood. It now draws and exhausts directly through the blower. An "air foil" was cut out because it was imploding without it. Smoke draws in from about 5-6 inches from the opening. How did I get around the corrosion thing you say? Dupli-Color Bed Armor. I know it probably won't hold up forever but for a while at least. Then I will get serious and build a good sized hood out of wood and get a real corrosion resistant fan. I see this as an inexpensive learning experience 8)


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## Geo

im sorry i just now started to read this post.to create the venturi effect the air supply must be constricted to create a vacuum behind the constriction.your blower would have probably been fine if you had used a smaller inlet on your blower than your supply.in other words you should have used a 2" pipe on the blower for a 4" supply. also use a "Y" fitting and use flex pipe on your blower so you can insert the smaller pipe past the "Y". i don't have a diagram so bear with me.the "Y" has 2 sides on one end and a single on the other. use one side of the "Y" for the blower and the other side as the supply and the single end is the exhaust. this should create the vacuum you are looking for. good luck.


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## Palladium

I am currently building a fume hood. Here is what i'm using to coat the hood as well as my counter tops with. http://www.homedepot.com/h_d1/N-5yc1v/R-202588482/h_d2/ProductDisplay?langId=-1&storeId=10051&catalogId=10053

http://protective.sherwin-williams.com/tools/epoxy-coating-troubleshooting/epoxy-coating-comparison-chart/

I was in Commercial coating for years and this should do just fine for the application at hand. For the price of 2 gallons you can't beat it and you should have plenty to do with what is needed. No you don’t use the chips. lol
.


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## eeTHr

I did an experiment on the venturi concept today.

First of all, in all the Internet research I did, the actual "venturi" concept was only using a duct with a restricted zone, called the "throat." The throat is a section in the duct which has a smaller cross section than either the air input section or the output section.

The point being that the original "venturi" didn't have any suction port. Mr. Venturi's concept only proved that as air (or fluid) passed through the throat, the air speed increased and the air pressure decreased. I couldn't find when or who came up with the idea of including a suction port.

It could be assumed that the suction port was a natural addition, because the decrease in air pressure would result in a suction. However, the only decrease in pressure is that which is relative to the pressure of the input air. That is, the throat still has pressure *above* that of the ambient air pressure from where the suction is to be drawn. Since the only history of the "Venturi Effect" includes just the input duct, throat, and output duct, with no suction port, I'm not sure that the suction effect should properly refer to the "venturi."

Further, since any suction is *not* produced by the decreased air pressure in the throat, then the venturi configuration might not be necessary to the creation of suction.

Rather, it seems like a restriction in the flow, with it's associated resistive losses, might actually be lessening the suction efficiency of any suction system which uses air flow to create it.

So I did this simple experiment---

A shop vac, 5.5 HP, with a 2" blower outlet on it, was used. The PVC and fittings were 2". The outside of the PCV pipe needed to be shaved down a little to fit into the shop vac air outlet. This resulted in a strong air flow, similar to a leaf blower. Leaf blowers appear to come in two general power ranges, about 6 Amps and about 12 Amps, so this should approximate the smaller power versions.

A 2"x2"x2" "T" fitting was placed onto the PVC pipe coming out of the shop vac. This made the suction port enter the system at an equal cross section point, rather than using a throat section. A suction was created at the "T". The suction was tested by putting a piece of notebook paper over the opening, and the suction would hold it there. If the paper was slid off the opening about 1/3 way, the suction would pull the edge of it inward about a half inch, indicating there was also some significant flow created, as it maintained some suction even with the opening present (made by sliding the paper back, producing a "vacuum leak"). Since there is not any vacuum or flow measuring devices handy, this is the best indicator which was available.

Next, a longer length of the PVC was attached to the "T" air flow output end. The suction port then blew air outward, instead of sucking inward. This indicates that at least half of the Venturi configuration is necessary to create suction, and that being the larger cross sectioned output duct. Apparently, using just the "T" connector alone, approximated the larger output section of the Venturi configuration, by allowing the air flow to exit almost directly into the surrounding atmosphere. So it appears that larger exhaust ducting is necessary to make the suction configuration work.

Since reducing the cross section, in order to form the traditional throat of the original Venturi configuration only produces a reduction of air pressure relative to the input air pressure, yet still greater than the air pressure in the hood, the necessity of going to a smaller pipe to create suction is questionable. And since it appears that air pressure is not what is creating the suction, it may be considered that it is instead the air _*speed*_ which is doing it.

At that point, the efficiency loss from the friction of the constriction of the throat, and the flow reduction of the suction caused by the constriction of the throat, should be factored in.

In other words, if the air speed is already sufficient, why constrict it by adding a smaller throat section? The combination of optimum air speed past the suction port, and size of the outflow duct from the "throat" area, in order to produce the maximum air _*flow*_ would need to be determined. So far, all the "venturi" suction devices I've seen on the Internet are designed only to produce and hold a _*vacuum,*_ rather than to produce a considerable air flow.

The multiple port configuration was also tested. Another "T" fitting was added directly to the existing one, without a piece of PVC (which would have constricted the flow slightly) in between. A suction was produced at the second fitting, approximately equal to the first. That's encouraging.

Also, several sizes of reducer fittings were plugged into the suction port of the single "T" fitting, when suction was being produced, but it did not increase the suction. It seem the only thing this did was reduce the suction air flow which would come from the hood. So it appears that the idea of using the "T" sections which have a smaller diameter pipe out the side, would not help the suction any.

It looks like the main factor, for producing suction, is, generally speaking, that the air duct outlet directly after the suction port have a larger cross section than the area prior to the port.

It also appears that multiple suction ports are the solution to maximum air suction flow.


Edit: Since the doubled up "T" connectors worked, it seems that the problem with adding the length of PVC to the single "T" connector was that the PVC _*inserts into*_ the fitting, thus _*reducing*_ the cross section at that point, and changing the dynamics of the duct at that point enough to cause air to flow _*out*_ of the suction port, rather than inward. So a continuously increasing pipe diameter is probably not necessary, but a way of connecting fittings would need to be found which would not cause any minor air restrictions. Even angle fittings might cause enough disruption to throw a system like this off-balance.

Last edit: Spelling of "produce" in 11th paragraph.


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## Barren Realms 007

That is pretty good eeThr. Could you take a 3" tee or a 4" tee and do the same test and see what you come up with? Would it be asking too much for you to try it with a wye as well to see what happens?

It sounds like Glondor's problem then is just that his hood is too far from his tee and if he get's it closer it might solve his problem.


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## eeTHr

Barren---

One of Glondor's problems was that he was dividing up whatever suction might be created at the suction "T" three ways, resulting in only 1/3 of whatever could be developed, at each suction pipe in his hood. That's a *parallel* configuration. What is needed for multiple suction points is a _*series*_ configuration for them.

The main problem, though, seems to be that he violated what appears to be the "equal or greater" rule for exhaust duct resistance. This is demonstrated by the above experiment where the same size PVC pipe was inserted into the output end of the "T." The PVC fittings have a larger inside diameter than the corresponding size of pipe, which allows the pipe to slide into the fittings (if they are the slip type of fittings). Since this small difference is significant to determining whether air flows in or out of the hood ports, then the length, and any change in direction, of the exhaust pipe is likely to affect that determination also, due to air resistance per foot from the straight ducting and also additional turbulence from the curves.

The basic rules of an airflow suction system would be the same for 3", or any size pipe, as it is for 2". I don't have a "Y" fitting here, but from what I've seen on the Internet, for various air and fluid flow-suction systems, it appears to me that the 90 degree suction port creates the most suction. I can pick one up on my next trip into town, and try it though.

goldenchild's post about Glondor's blower being on the wrong side of the run past his hood ports, and his multi-port diagram is what got me thinking about all this. And that's how I realized that a parallel hood port setup would produce less flow in each one. But there should be _*some*_ suction produced, rather than air blowing _*into*_ that hood. So that's where the exhaust duct being equal or greater in size comes into play, along with the equivalent of duct size reduction by the air resistance of the ducting length, and the turns made by the angle fittings.

So far, it seems that going one or two sizes larger in the pipe, after the "T" or a series of them, especially for a long exhaust duct run, or one with a few turns in it, would be necessary.

I'll post whatever the results are.


----------



## eeTHr

P.S. I would also think that the volume of air being sucked from the hood, being added to that already in the flow from the blower, would affect the speed/pressure computation in the following suction ports and exhaust ducting.


----------



## eeTHr

I thought of another test that I could do with the materials that I have on hand now.

Since adding the PVC pipe to the air output end of the "T" fitting caused the air flow to reverse in the suction port, and blow toward the hood instead of sucking inward and going out the exhaust, and since I realized that the PVC was actually smaller on the inside diameter than the same size "T" fitting, I thought it would be good to see if the problem was caused by the size of the exhaust pipe in relation to the size of the suction port, or in relation to the size of the air input PVC pipe from the blower.

I had already tried all of the reducer plugs, when the exhaust PVC pipe was attached to the output of the "T," with the result being that air still blew out of the suction port, rather than sucking in. But just as a confirmation, I tried putting the same size PVC pipe into the sucktion port, so now all the three openings of the "T" had the same size pipes.

In addition, I made both the exhaust PVC pipe piece and the suction port PVC Pipe, the same length, to eliminate any slight air resistance difference.

But air still blew out of the suction port, rather than sucking inward.

So right now the formula seems to be that the exhaust duct needs to be larger than the inflow duct from the blower. I take it that this is either because the speed/pressure differences of the larger cross section is what creates the suction, or that the added volume of air from the suction port adversely changes the dynamics of the exhaust ducting. Probably because the pipe from the blower is already allowing as much air flow as it can, for it's given pipe size and air pressure from the blower, and adding more air volume from the suction port merely creates a greater density of air in the exhaust which makes more back-pressure against the forward inflow from the blower, and thus stops any vacuum production. I guess it creates a state of equilibrium between the suction port and the exhaust, and the "T" becomes an ordinary forward-configured "Y," simply splitting the air flow to go out both of the open ends.

Incidentally, the "Y" fitting would be placed backwards from this hypothetical equivalent if it was used, instead of a "T," to try and create a suction.)

I would modify the suggested formula or rule, above, to say that the total air *resistance* needs to be less in the entire exhaust ducting system, than in the input ducting system from the blower, plus some amount inversely proportional to the added air volume from the suction port.


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## Barren Realms 007

Too many variables to say exactly. Best bet is to make sure your exhaust is larger than your incoming air port to create the suction. You did a good job on this. Thanks


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## eeTHr

Barren---

Yes, but too many bends in the exhaust ducting could drag it down also.

And the more hood ports, the larger it will need to be, too.


I needed to go into town, so I swung by the Ace Hardware for a 2" and a 3" "Y," and a 2" to 3" reducer. *They don't have any "T" fittings larger than 2".*

Replacing the 2" "T" with the 2" "Y" fitting, resulted in slightly less suction. The funny part was that it worked almost the same in either direction, with it "forward" or "backward." Backward, it had some vibration to the suction, and was a little weaker.

The inner diameter of the 2" "Y" was smaller than the inside of the 2" "T." The "T" is 2 5/16", while the "Y" is the same ID as the PVC pipe---exactly 2". Maybe the "Y" needs more strength because the the hole in the side is longer due to the entry angle. They are both by the same company. But the smaller inner diameter could be the reason the 2" "Y" didn't give as much suction as the "T".

So then I put the reducer and the 3" "Y" on there, with the suction part slanting forward (toward the exhaust) as it goes into the fitting, and there was about twice the suction as with the 2" "T". Moving the paper to give a 1/3 opening (vacuum leak) still gave suction, so the air flow volume was also increased.

I would envision the best chance of a workable system to be three or four "T" joints, close together, with slightly increasing connecting pipe size between them, and a larger size exhaust ducting system, as short and with as few bends as possible. And a 12 Amp blower for 115V, 15 Amp, service outlets.


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## eeTHr

P.S. There may also be increased performance by modifying the area where the suction port meets the split fitting. I know that certain flow disruptions in water lines with a high flow rate, will cause such a vacuum that air bubbles will spontaneously form, which can cause the pumps to become inefficient and over heat.

So it may be possible to create more suction than a simple joining of the suction port pipe, by fashioning some type of baffle in there.


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## eeTHr

P.S.S. I tried both sizes of "Y" fittings with the air blowing into the angled port of them, instead to into the end of the straight section. They both blew air *out* of what would then be the "suction" port. So that would be another problem with Glondor's original setup.


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## Barren Realms 007

eeTHr said:


> Barren---
> 
> Yes, but too many bends in the exhaust ducting could drag it down also.
> 
> And the more hood ports, the larger it will need to be, too.
> 
> 
> I needed to go into town, so I swung by the Ace Hardware for a 2" and a 3" "Y," and a 2" to 3" reducer. *They don't have any "T" fittings larger than 2".*
> 
> Replacing the 2" "T" with the 2" "Y" fitting, resulted in slightly less suction. The funny part was that it worked almost the same in either direction, with it "forward" or "backward." Backward, it had some vibration to the suction, and was a little weaker.
> 
> The inner diameter of the 2" "Y" was smaller than the inside of the 2" "T." The "T" is 2 5/16", while the "Y" is the same ID as the PVC pipe---exactly 2". Maybe the "Y" needs more strength because the the hole in the side is longer due to the entry angle. They are both by the same company. But the smaller inner diameter could be the reason the 2" "Y" didn't give as much suction as the "T".
> 
> So then I put the reducer and the 3" "Y" on there, with the suction part slanting forward (toward the exhaust) as it goes into the fitting, and there was about twice the suction as with the 2" "T". Moving the paper to give a 1/3 opening (vacuum leak) still gave suction, so the air flow volume was also increased.
> 
> I would envision the best chance of a workable system to be three or four "T" joints, close together, with slightly increasing connecting pipe size between them, and a larger size exhaust ducting system, as short and with as few bends as possible. And a 12 Amp blower for 115V, 15 Amp, service outlets.



Yes too many bends will cause problems, air turbulance that disrupts the flow.

That is interesting that the wye worked in either direction. I have never taken the time to measure the inside diameter of the fitting's and didn't know there was a difference. I have a bunch of older fittings I picked up years ago I will measure them when I get time and see if that is something that they have changed in the last few years. The wye is made stronger because of the stress it is put under for the applications it is used for.

If you use a 12 AMP blower I would suggest using a 20 AMP receptical because you will end up causing a 15 AMP receptical to over heat under continuous use conditions and possibly cause serious damage.


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## Barren Realms 007

eeTHr said:


> P.S. There may also be increased performance by modifying the area where the suction port meets the split fitting. I know that certain flow disruptions in water lines with a high flow rate, will cause such a vacuum that air bubbles will spontaneously form, which can cause the pumps to become inefficient and over heat.
> 
> So it may be possible to create more suction than a simple joining of the suction port pipe, by fashioning some type of baffle in there.



When a pump does this is is called cavitation.



> P.S.S. I tried both sizes of "Y" fittings with the air blowing into the angled port of them, instead to into the end of the straight section. They both blew air out of what would then be the "suction" port. So that would be another problem with Glondor's original setup.



That was why I suggested he change that part in the first place.


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## eeTHr

Barren---

I figured they limited the leaf blowers to 12 Amps just because 15 Amp breakers are so common.

That's the word for it---cavitation. It can also do that within the PVC run, itself, I think at the turns, if the flow is high enough. A partially open valve can do it also.

I know you suggested to Glondor that he turn the "Y" around and put the main air flow through the straight section. That's why I thought of confirming that for anyone interested.

It would be interesting to see how many CFMs it can be gotten up to with air suction techniques. If the cost of a regular blower plus PVC fittings turns out to be significantally less than the cost of an acid resistant blower, it would certainly encourage more beginners to build and use fume hoods.


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## goldenchild

eeTHr,

Can you draw a diagram of what you envision to be the most efficient setup?


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## eeTHr

goldenchild---

Yes, but I have changed my mind about what seems to be the optimum configuration several times since my last post!  

It's a strange story---

I was looking at the 2" pipe with the 3" reducer going into the 3" "Y" fitting, and trying more things, with it attached to the shop vac today. Mainly trying to figure out where the suction comes from, and how the larger size "y" fitting actually works to enhance it.

I came up with three things.

First, if I inserted a 2" PVC pipe into the suction port of the 3" "Y" connector, the suction up the 2" pipe increased when I pushed it up into the air stream within the 3" fitting. I thought it seemed like it would do that, but wasn't sure if having the 2" pipe up in there wouldn't bog down the air flow, and just prevent any increased suction. But it worked.

Secondly, I got to wondering how that would affect more suction ports in a multi-port system. Maybe having that suction pipe sticking into the air stream would mess up the downstream suction ports?

Third, I was wondering how the additional volume of air coming up through the suction port would affect the air density/pressure in the main blow-flow line. That, as well as turbulance from the first suction pipe being right in the air stream, might just counter any additional suction possible from additional suction ports.

So to get back to your question, I was then thinking, with the test setup I'm working with, the best configuration would be the 2" ID PVC pipe for air entry from the blower, going into a 2" to 3" reducer which goes into a 3" "Y" fitting. Then for the suction, a 2" PVC pipe going into a reducer to the suction port of the 3" "Y", but with the stop flange inside that reducer ground off to allow the 2" pipe to pass through and penetrate the air flow area.

Penetrating the air flow puts the air stream all around the suction pipe opening, making more "cavitation" area, and creating more suction. Cutting the suction pipe, on the end which goes inside the air stream, at a 45 degree angle, would result in, when that angle is combined with the 45 degree angle of the "Y" fitting's suction port, making the 2" suction pipe end-cut to be at a 90 degree angle to the blower air flow, creating even more opportunity for "cavitation" suction. But the bottom of the 2" suction pipe air stream opening is blocked from the blower air flow, by the 2" pipe, itself. So adding a collar to it, to extend straight down the center of the air stream far enough to go past the turbulance caused by the entrance of the 2" pipe, would allow the cavitation effect to exist completely around the 2" pipe tip in there. This would require a 22 1/2 degree cut on both the 2"suction pipe and it's collar.

At this point, I was thinking that a single-stage, rather than a multi-port, configuration would probably be more efficient, because of eliminating the efficiency losses at each port, and turbulence, and so forth.


But---the major problem with all this is that the thing *now resemples the drawing from Ammen's book,* which jimdoc posted on the first page of this thread!

So, it's gone full circle! Oh no's!

Which figures, because why would he put it in his book, unless it was the optimum configuration. They must have already worked this all out.

So, why didn't Ammen's setup work for glondor? It seems to me it's probably because he used a 3" going into a 4". the cross sectional area of a 3" ID pipe is 7.07 sq. in., and the area of a 4" is 12.56 sq. in. That's less than double the area of the 3". Is it that it must be at least twice the cross area? Or did he have too many bend fittings, which would reduce the the flow as much as a smaller cross area? Or both?

Another interesting point about Ammen's configuration is that it is just the opposite of the one which I was setting up and testing, above. In Ammen's, the blower air comes in via the smaller pipe, and goes down the larger pipe. In the setup I was testing, the blower air feeds the larger diameter pipe fitting, and the suction is drawn out of the smaller pipe which is inserted into the larger diameter fitting. Does this make a difference? Does Ammen's design create cavitation around the *outside* of the smaller blower air feed pipe, instead of creating it on the _*inside*_ of the smaller suction port pipe like the arrangement that I was testing? Apparently it does, because supposedly it works.

I don't have a cad program, and the only scanner is connected to my wife's computer, and it's late, so if you still want a diagram of the "Y" fitting configuration, I'll have to do it tomorrow.

As for me, I need to pick up another reducer, so I can test the suction with it stuck into the air stream, and with the 45 degree angle on the air stream end, and also with the extension collar.

It might turn out to be easier and less expensive in fittings costs, to just use a 3" 90 degree fitting, and drill a hole in the corner of it, and pass the 2" suction pipe into that and far enough up it and into the following ducting, to get past any turbulance from the 90. And the 2" air feed pipe from the blower would go through a reducer into the 90, on the other end from the one that the 2" suction port goes down. And that would make it look even more like Ammen's drawing in reverse.

Which brings up the question of, if the same 90 were used, but in reverse, with the blower fed through the 2" pipe going in through the corner of the 90, would the end of the 90 without the blower pipe going up it, then become the suction port, as in Ammen's diagram? I guess it would. And is one of these configurations more efficient than the other? I'm guessing they will be the same. Except that if you blow through the smaller pipe, into the 90, and suck through the other end of the 90, *you then eliminate two reducer fittings, and their cost.*

Whichever way the venturi design goes, I think it's going to be very important to remember to compensate for whatever bends are in the exhaust ducting system, probably by going to a larger size than the venturi fittings section, which in my test case would be going to 4" exhaust ducting out of the 3" venturi casing.

If a system starts with 3", 4", or larger, out of the blower, the cross sectional area calculations are going to be very important, also ( 2 pi r squared).

I think that the maximum suction flow for a venturi system is going to turn out to be around half the CFM of the blower air out of it's feed pipe to the venturi unit. But I think the whole thing, with twice the size of blower, and the larger ducting required, would still be less expensive than an acid proof blower, unless you have a really long ducting run.


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## shyknee

Here is my 2 cents, maybe someone can draw it out better, hope this helps.


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## goldenchild

Blower has to be before the "throat". Suction is created locally at the throat. Think of how this airbrush gun works.


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## shyknee

yes and as in the air brush model the exit or exhaust is very close to the throat or venturi .
what is missing is the restriction 4metals spoke about at the y or t .
There should be no elbows or other restrictions after the venturi just straight exhaust .
hope this helps I used your picture to express my view of what should work, hope you don't mind goldenchild.


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## eeTHr

shyknee---

I like your idea with the piece of plexiglass. It looks easy to make, too.

But so far, I don't see any point in restricting the air input flow to less than the area of the air input duct. It causes a loss in system efficiency for no reason. It looks like it would work if the "Y" was about twice the diameter of the blower air input duct, but I don't know what the efficiency would be, compared to having the suction port pipe totally inside the air stream.

A suction can be created by extending the suction port up into the air stream of a larger diameter throat, rather than the traditional smaller throat of the original Venturi design, without restricting the main air flow of the input from the blower.

The traditional Venturi configuration had no suction port, and the smaller throat section had the purpose of creating a way to have a different air speed versus pressure, in the same pipe line, and thus make a measurement of both sections at the same time, proving the trade-off of less pressure when speed was greater. This is like Ohm's Law for the electrical circuit current versus voltage trade-off.

So it appears that the initial restriction is not necessary in an air suction system, because if higher air speed over the suction port is desired, you can just get a bigger blower---rather than restricting the one you have, which would reduce it's efficiency.

With the suction pipe completely inside the stream, the cavitation effect would be developed for the length of the circumference of the pipe, which would be 3.14 times longer than the edge of the plexiglass piece. So I think the pipe extension would create more suction than the plexi baffle.

If I can find a small scrap cooling fan from one of the computer video boards, I think it would make a good air flow indicator. It should work in reverse, and put out a DC voltage, when it is spun by an air flow, and that voltage can be read on a meter. This won't be calibrated to read CFM, but it will work to compare blower output with the suction flow, and show any increase in suction for various configurations of the Venturi.

I'm not sure if the readout would be linear or not, that is, if twice the voltage would indicate twice the CFM, but putting one over both outputs of a "Y" connector would give a reading for half of the blower output, then measuring the blower output directly will give the reading for twice the air flow, and that should give an idea of how proportional the voltage output is to the different air flows.

I was up late last night making my previous post, so now I need to get some breakfast and stuff, then see if I can do the fan tests.


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## eeTHr

P.S. If anyone is wondering if the exhaust ducting resistance is all that important to consider, just think of it this way---everything always takes "the path of least resistance."

So if the exhaust presents even slightly more back-pressure than the suction path, it will blow air out the suction port.

And as the exhaust resistance approaches that of the suction port, the suction starts to reduce.

For air suction configurations, the Venturi Effect which applies, is the larger diameter outflow duct, not the smaller diameter throat.


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## shyknee

eethr


> But so far, I don't see any point in restricting the air input flow to less than the area of the air input duct. It causes a loss in system efficiency for no reason. It looks like it would work if the "Y" was about twice the diameter of the blower air input duct, but I don't know what the efficiency would be, compared to having the suction port pipe totally inside the air stream.
> 
> A suction can be created by extending the suction port up into the air stream of a larger diameter throat, rather than the traditional smaller throat of the original Venturi design, without restricting the main air flow of the input from the blower.





Yes, I agree totally.
I just can not test it at this time


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## goldenchild

So what I think you guys are saying is something like a 3 inch system with a 3 inch to 1.5 inch "T" for the throat? And a 1.5 inch pipe slighty extened into the blowers air flow path? Or just 3 inches all around? You would then have to test efficiency with how far up into the airflows path the pipe would go.







P.S.
I orginally tried the 3 to 1.5 inch T without a pipe in the airflow path and can tell you that air was blow *into* the hood.


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## Barren Realms 007

goldenchild said:


> So what I think you guys are saying is something like a 3 inch system with a 3 inch to 1.5 inch "T" for the throat? And a 1.5 inch pipe slighty extened into the blowers air flow path? Or just 3 inches all around? You would then have to test efficiency with how far up into the airflows path the pipe would go.
> 
> 
> 
> 
> 
> 
> P.S.
> I orginally tried the 3 to 1.5 inch T without a pipe in the airflow path and can tell you that air was blow *into* the hood.



It might work better if you have a 90 on the smaller pipe inside the tee faceing downstream.


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## shyknee

don't forget the baffold is most important.


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## eeTHr

Barren Realms 007 said:


> It might work better if you have a 90 on the smaller pipe inside the tee faceing downstream.




Barren---

I think that is true.

It seems that, besides the suction port style, the most important thing is that the output duct's cross sectional area needs to accomodate the volumes of the blower air flow _*plus*_ the added air from the suction port. Apparently this needs to be true from the beginning of the suction port, onward.

I think that a suction port which is smaller than required, will only restrict the suction, however.


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## eeTHr

Here is a diagram of what I think will work best for a "Y" fitting suction Venturi, from what I have tested so far. Note that I haven't tested the 45 degree cut in the protruding suction port, nor the collar.

It's a little sloppy, because I just used a draw program instead of a CAD.










It might turn out that using the large 90 degree fitting for the Venturi casing is more efficient. Or reversing the blower input and the suction pipe, as in Ammen's diagram, might be even better.

Also, it might be better to make the Venturi section longer, to accomodate making the suction collar longer in order to put the cavitation area at the end of it further away from the turbulence caused by inflow air hitting the back of the suction pipe.

Note that the larger size of the exhaust ducting is not to create suction, but to prevent back pressure from air friction against the inside of the ducting run plus any turns in it. The "Y" fitting, acting as the Venturi casing, is already larger, to accomodate both the blower inflow air and the additional air entering the system from the hood, through the suction port. By having enough cross sectional area to handle both air flows inside the Venturi section, it allows the cavitation to form at the end of the suction collar and create the suction effect without having back pressure cancel it out.


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## eeTHr

shyknee---

I only now noticed that what you drew in your venturi drawing is of the style which is in Ammen's book, shown on the first page of this thread.

I like the use of the "Y" better than the large 90 degree fitting that I thought of for his method. Your "Y" arrangement has 45 degrees less drag, and could simply go into the hood at 45 degrees.

It looks like it only requires the "Y" fitting and an end cap for parts, too. Plus making a hole in the end cap for the blower pipe. In both the large 90, and your "Y" fitting configurations, some kind of additional support for the blower pipe will be most likely be needed, but that could probably be easily provided by extending the blower mounting platform and strapping the "Y" to it, or to a vertical backing added to the platform.

It should be remembered that with multiple hood ducts, the total suction will be split among them. And the ones toward the far end of the suction ducting run might not draw very much if the hood down-pipes are all the same size.


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## glondor

I gave up on venturi for now. I priced an acid resistant blower and the price was 4400 plus taxes. Out of the picture for me. I will use a sacrificial system for now with the blower in the stream. Main blower at top left on top. Smaller blower inside hood for lower level air flow. Ducted to main blower intake. Few minor kinks, works well until I come up with something better. No fumes in the work-space with full on nitric boil. Using an ice cream tub and marbles as a bit of a condensor. I will work a new system in the empty right side of the hood with a proper scrubber and proper blower. 




Here is my daughter holding our first real gold bar.


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## eeTHr

glondor said:


> ...Few minor kinks, works well until I come up with something better.





I know what you mean. I used a shop vac, and put three coats of teflon spary-can paint, from a hardware store, on the empeller. I used it about a dozen times, took it apart, and couldn't tell any difference. It's the same one I am using to experiment on the venturi configurations with.

I might even just end up using it in the regular way, too. After all, it has both the inner bag filter, and the cylindrical filter cartridge. (I got it at Walmart.)

I tried using it to suck the air from the hood, through standing water, by putting a 4" PVC from the hood into a plastic garbage can with water in it. But all the ways I tried it, the air flow was very poor.

I did discover, however, that just directing the hood pipe downward at the water, and about an inch or so off the surface, built up a large amount a acidity in the water after just a couple of uses that way. It appears that most of the air was actually contacting the water surface, and the water was capturing lots of the fumes right there. I'll have to tape some litmus paper in the end of the exhaust duct, when I get my new fume hood built, and see about how much of a difference it makes compared to litmus taped directly inside the end of the hood outlet for the same amount of time (like 60 seconds). It might work good enough for occasional refining.


P.S. Nice bar!


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## eeTHr

Well, I tried the 45 degree angle on the 2" suction pipe, extending it up into air stream of the 3" "Y" fitting. It did increase the suction. I haven't dug up a small video card fan to make meter measurements yet, but I tried a piece of notebook paper, holding it away from the pipe, and slowly bringing it closer. It slaps it up against the 2" pipe opening when it comes within an inch away from it.

If I have time, I'll try it after adding the collar piece, tomorrow.


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## goldenchild

glondor said:


> I gave up on venturi for now. I priced an acid resistant blower and the price was 4400 plus taxes. Out of the picture for me. I will use a sacrificial system for now with the blower in the stream. Main blower at top left on top. Smaller blower inside hood for lower level air flow.



For what its worth. You should coat those blowers with the stuff I pictured above. My blower is holding up extremely well. Even after some aggresive AR reactions. I am very surprised. 

Just take the blowers apart and put it on nice and thick on all pieces. It dries fast too. Using it like you have now wont hold up for long at all. Especially when the AR hits. Keep in mind they also sell plasic fan wheels. Good luck.


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## eeTHr

Well, I did add the collar piece the other day, but had varying results.

Because I was using the 3" suction port pipe inside the 4" "Y" suction port, there was a void area at the base of the sustion pipe, inside the "Y." I had simply stuffed some thin filler paper around the 3", in order to hold it in and make it air tight around it. But the filler paper only went as far as the wide part of the end of the "Y" fitting which is supposed to have a 4" PVC stuck into it. This created a cavity or void, below where the intake of the suction 3" with the collar was.

If the pipe was tilted so that the collar intake was forward, no suction resulted. But if I tilted it back as far as it would go, it sucked better than just the 45 degree cut.

My next thought was to extend the collar 8" or so into an added 4" PVC section, so as to get the intake out of the turbulence area of that void/cavity. But there is no way to glue an 8" collar on, and then be able to insert it into the "Y" fitting.

So, the best shot at that kind of extension into the smooth air flow area is to go with the Ammen design, and have the blower enter the "Y" with an extended 3" and go past the suction port of the "Y" and into the added section of 4" PVC. This would require no bends in the 3", and then the suction port can remain the regular 4" of the "Y" fitting. So that's my next try.


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## eeTHr

Here is the Ammen type suction venturi. I tried it today, and it seems to have about twice the suction force as the best of the other type which I tested, above.

But this version has a full 3" suction port. It will suck a piece of notebook paper from 2", instead of the 1" of the previous versions. However, from a 3" opening on the hood end, that means over twice the cross sectional area as the previous suction port of only 2" diameter PVC pipe, so it probably means around *four times* the overall suction volume.

But it still feels like less than half of the shop vac's direct suction power.

It is much simpler to build, and with fewer fittings, it costs less, too.

This is what it looks like---






It will suck out the flame of a Bic lighter at 1", which is pitifully weak. However, this shop vac which I'm using for testing is only 5.5 Amps, and that's why the "blower input" PVC pipe is only 2" diameter. Actually, the hose for this vac is only 1 1/4" inside diameter, but the vac port is 2".

A larger, more efficient blower would probably provide plenty of suction for a fume hood adequate for home refining. There is one listed for only $46.49 ($43.50 less than this shop vac I'm testing with cost) at Lowe's, and, because of the vac's 1 1/4" ID hose, I assume that this blower has way more air volume.


Last edit: Added word "vac" after "shop," and changed "vac post" to vac port," in paragraph 6.


----------



## eeTHr

(Note: This post pertains to my previous post, on the preceding page.)

Here are some blowers I found---

Harbor Freight, $49.99
This one puts out 300 CFM. Maybe not quite enough air volume.

Home Depot, $49.00
3 speeds, up to 310 CFM. Same comment as above.

Lowe's, $46.49
480 CFM, but only has one review, and it sounds like it had a factory defect. *If the venturi can suck at only 41.7% of the blowers direct CFM, this would produce 200 CFM of suction, which would be enough for a fume hood door opening of 12" x 24" or 17" x 17" or 15" x 19" (at 100 CFM per square foot of fume hood door opening).* The Ammen venturi style shown in the diagram on my previous post, tests-out to be the most efficient so far---probably right around the 40-something percent required for this blower.

Harbor Freight, $74.99
Switchable, either 1400 or 1575 CFM. I wonder what would happen if you mounted this on a skateboard with a really long extension cord?


----------



## goldenchild

eeTHr said:


> Harbor Freight, $74.99
> Switchable, either 1400 or 1575 CFM. I wonder what would happen if you mounted this on a skateboard with a really long extension cord?



You got me excited for a sec. I thought it was a squirrel cage type. With the way mine is holding up so well I could build a much bigger hood with 1400 cfm. These are the cheapest acid resistant blowers I could find online.

http://www.drillspot.com/products/587555/plastec_pla15st2p_direct_drive_forward_curve_blower

I see a cfm of 550 but don't know what this means. "CFM @ 0.500-In. SP"


----------



## eeTHr

goldenchild---

No, it's not acid resistant, because it relates to the venturi setup on the previous page.

That blower you linked to looks like a turbocharger! Too bad it's soo expensive. That's why I took such an interest in the venturi system configurations.

CFM is Cubic Feet per Minute of air exchange, or air flow volume.

SP is Static Pressure. Basically that's loss from the air intake and exhaust ports' limitations.


----------



## goldenchild

I don't plan on buying one of the expensive blowers as long as the kind I have now holds up for a decent amount of time. 

I knew cfm was cubic feet per minute but didn't know what the part in quotes meant "CFM @ 0.500-In. SP". Do you or anyone else know how to translate that into a sentence?


----------



## eeTHr

goldenchild---

Here's a post by samuel-a that shows a diagram of it.

That post is from this thread.

I was searching for other fume hood threads, and found that if you put "fume hood" as the search term, and then down in the lower right corner click the radio button "Topic titles only," you get just the first post from each thread, instead of every post which contains those words. that method works a lot better for certain searches.


----------



## eeTHr

Here some actual photos of the PVC assembly for the Ammen type Suction Venturi---

Overview with an exhaust section






Suction port side





Other side





Adapters view





Inside venturi from output end, without exhaust extension on






The 45 degree fitting is because my shop vac outflow port is at an angle. That goes into a reducer which is made of black ABS type of plastic, because that's all they had at my local ACE Hardware (it's kind of a small town).

The black fitting which connects the 3" "Y" to the 3" _*thinwall*_ PVC is actually Gorilla duct tape, because that's what I had on hand. The thinwall, I believe it's called schedule 20 (whereas the "Y" fitting is schedule 40), is much less expensive than the thicker pipe, especially in the larger diameters. So the Gorilla tape is merely to increase the outer diameter of the thinwall exhaust section, to fit into the sched 40 "Y" fitting.

The grey 2" PVC is for electrical runs, whereas the white is for water. You can see where I tapered the end of the 2" pipe which comes out of the 45 degree fitting, in order to fit into my shop vac output.

Although this vac has 2" ports, it's hose is only 1 1/4" ID, so it's not the strongest air flow shop vac on the market, by far. That's why, even though this test setup resulted in suction which was too weak for fume hood use, I think the venturi system has a chance of working satisfactorily in a home refinery scenario, if one had a larger blower and used larger diameter PVC and fittings.

P.S. Although the end view of the inside of the venturi looks like the cross sectional area around the outside of the 2" PVC pipe is smaller than that of the inside of the 2" pipe, it calculates to be 3.93 square inches around that outer circle, compared to the 2" pipe which has 3.14 square inches.

Also note that the white "Y" fitting has a larger diameter at the *very ends,* to accomodate the outside diameter of the thicker schedule 40 PVC. Also, the PVC pipe walls get thicker as their diameter increases, for both sched 20 and 40.

P.S.S. To get the 2" air input pipe, from the vac output, to pass through that black reducer, I removed the stop-lip inside it, with a Dremel barrel sanding bit (it has a replacable sandpaper tube). This lip is inside the reducer, to provide a stop for the smaller PVC pipe to bottom-out on when assembled. This, and attaching to whatever kind of blower one uses, are the only modifications which are required beyond parts which can be purchased. And I am assuming that where I used the Gorilla tape, an adapter can be bought to be used instead.


Edit: Corrected "especiall" to "especially," in paragraph 3.


----------



## seawolf

At Harbor Freight they have a dust collector that might be used for a fume hood.
$129.99
120 vac
1 HP motor
4" intake 
4" exhaust
660 CFM
The housing is metal and I think the fan is a hard plastic.
From some of the posts I have read the housing could be disassembled sanded and repainted with a good epoxy paint to prevent corrosion. Then vented into a scrubber before gasses are released into the outside air.


----------



## eeTHr

I like it. The price isn't bad, the CFM seems good, and it looks like it would be easy to connect up-to.

I wonder what kind of plastic, and whether the acids would damage that?

Actually, some of the blowers that I linked to, could have plastic blades, too. Certain kinds of plastics can be a problem, I think.

But 4" blower pipe going into a 6" "Y" fitting would work for the venturi effect, cross sectional wise. And in that case, the plastic wouldn't matter, and it wouldn't require painting. And if it gave only 40% of the rated CFM in suction, then it would provide enough suction for a 2.65 square foot door opening.


----------



## qst42know

goldenchild said:


> eeTHr said:
> 
> 
> 
> Harbor Freight, $74.99
> Switchable, either 1400 or 1575 CFM. I wonder what would happen if you mounted this on a skateboard with a really long extension cord?
> 
> 
> 
> 
> You got me excited for a sec. I thought it was a squirrel cage type. With the way mine is holding up so well I could build a much bigger hood with 1400 cfm. These are the cheapest acid resistant blowers I could find online.
> 
> http://www.drillspot.com/products/587555/plastec_pla15st2p_direct_drive_forward_curve_blower
> 
> I see a cfm of 550 but don't know what this means. "CFM @ 0.500-In. SP"
Click to expand...


Be careful of that motor voltage (230/460 V) if you don't have access to three phase power. *If *the power company will provide it where you intend to work it can be extremely expensive to have it installed.


----------



## Geo

something no one has mentioned yet. i know the dynamics of how this works because ive dealt with it for many years at my old job only it was water but still the same effect. the pressure going in works better at the exhaust end, in other words the farther you put the pressure inlet from the fume hood the stronger the vaccum will be. it would be better if it were at the last couple of feet at the end of the exhaust. think of it as a sand blaster and the feed tube in the sand as your fume hood. the air pressure comes in just behind the nozzle where the sand comes out. same difference with this the vaccum is greater this way.


----------



## eeTHr

Geo said:


> something no one has mentioned yet. i know the dynamics of how this works because ive dealt with it for many years at my old job only it was water but still the same effect. the pressure going in works better at the exhaust end, in other words the farther you put the pressure inlet from the fume hood the stronger the vaccum will be. it would be better if it were at the last couple of feet at the end of the exhaust. think of it as a sand blaster and the feed tube in the sand as your fume hood. the air pressure comes in just behind the nozzle where the sand comes out. same difference with this the vaccum is greater this way.




That makes sense, because that way there is almost no back-pressure reducing the venturi effect.

So the previous ideas of putting the blower in front of a string of venturis would probably be very difficult, if not impossible, to optimize.


----------



## eeTHr

qst42know said:


> goldenchild said:
> 
> 
> 
> 
> 
> eeTHr said:
> 
> 
> 
> Harbor Freight, $74.99
> Switchable, either 1400 or 1575 CFM. I wonder what would happen if you mounted this on a skateboard with a really long extension cord?
> 
> 
> 
> 
> You got me excited for a sec. I thought it was a squirrel cage type. With the way mine is holding up so well I could build a much bigger hood with 1400 cfm. These are the cheapest acid resistant blowers I could find online.
> 
> http://www.drillspot.com/products/587555/plastec_pla15st2p_direct_drive_forward_curve_blower
> 
> I see a cfm of 550 but don't know what this means. "CFM @ 0.500-In. SP"
> 
> Click to expand...
> 
> 
> Be careful of that motor voltage (230/460 V) if you don't have access to three phase power. *If *the power company will provide it where you intend to work it can be extremely expensive to have it installed.
Click to expand...



Wow, I didn't notice that. 3 phase, too. And only 560 CFM max. That seems strange, because 1/2 HP motors run fine on 110 VAC, and are common. :?:

Makes the Harbor Freight unit look a lot better, and the venturi method.


----------



## Barren Realms 007

eeTHr said:


> qst42know said:
> 
> 
> 
> 
> 
> goldenchild said:
> 
> 
> 
> 
> 
> eeTHr said:
> 
> 
> 
> Harbor Freight, $74.99
> Switchable, either 1400 or 1575 CFM. I wonder what would happen if you mounted this on a skateboard with a really long extension cord?
> 
> 
> 
> 
> You got me excited for a sec. I thought it was a squirrel cage type. With the way mine is holding up so well I could build a much bigger hood with 1400 cfm. These are the cheapest acid resistant blowers I could find online.
> 
> http://www.drillspot.com/products/587555/plastec_pla15st2p_direct_drive_forward_curve_blower
> 
> I see a cfm of 550 but don't know what this means. "CFM @ 0.500-In. SP"
> 
> Click to expand...
> 
> 
> Be careful of that motor voltage (230/460 V) if you don't have access to three phase power. *If *the power company will provide it where you intend to work it can be extremely expensive to have it installed.
> 
> Click to expand...
> 
> 
> 
> Wow, I didn't notice that. 3 phase, too. And only 560 CFM max. That seems strange, because 1/2 HP motors run fine on 110 VAC, and are common. :?:
> 
> Makes the Harbor Freight unit look a lot better, and the venturi method.
Click to expand...


Commercial use. We put a number of 3PH blowers for fume hoods in a science lab for fume hoods.


----------



## eeTHr

Barren Realms 007 said:


> eeTHr said:
> 
> 
> 
> 
> 
> Yeah, 3 phase is common in commercial and industrial buildings. It's more efficient. But I've usually only seen it in the higher horsepower motors, where electricity savings can be significant. But I guess if there are several of the 1/2 horse, it does make a difference.
Click to expand...


----------



## Harold_V

Barren Realms 007 said:


> Commercial use. We put a number of 3PH blowers for fume hoods in a science lab for fume hoods.


For VERY good reason, too. Single phase motors are noisy. Very noisy. They hunt contantly, introducing vibrations and other annoying sounds that are absent from three phase motors. 

Harold


----------



## eeTHr

Harold---

I've delt with many, many electric motors, in the range of 1/3 HP to 2 HP, used in automated machinery. The smaller ones in single phase, and larger ones 3 phase, with the middle range in both versions. I knew the 3 phase were more efficient, and I know the differences in how they are built and how they work, but I never, ever, considered the fact that the 3 phase were also smoother running!

Now that you mention it, there was a 5 HP electric motor/generator unit, which converted 3 phase to single phase, in one place I worked. I was always amazed at how smooth and quiet it ran, for it's size. You just put 2 + 2 together for me. Thanks (again).


----------



## eeTHr

I thought that my previous photos of the test venturi might be a little confusing, because of the exhaust extension and angled input, so I made some with just the venturi section to show how simple it, itself, actually is---


Venturi Section






Suction Port View (please disregard the tan leaf on the left end!)






Blower Input and Reducer






Output End






Overall View, Including an Exhaust Section and Angled Blower Air Input






I angled the blower air input, only because my shop vac output is at an angle.

The venturi section, itself, consists of only three pieces: The grey PVC blower air input pipe, the black ABS reducer (which holds the blower air input pipe), and the white PVC "Y" fitting. (The black reducer between the "Y" fitting and the exhause section is actually Gorilla tape, because that's all I had on hand. It was necessary only because the exhaust section was thinwall PVC, so it has a smaller outer diameter, and the "Y" fitting is built to accept schedule 40 PVC into it, instead. But the sched 40 is more expensive!) Also note that the ABS reducer requires the inside retaining rim to be removed, to allow the blower air input pipe to slide all the way through it, and past it, and partially into the exhaust ducting.

This is a test version, using smaller ducting and venturi section than may be required, because it fit my shop vac used for the tests.

The reducer plugged into the venturi section is black because it is ABS plastic, used for sewer pipes, because that's all they had for that at my local ACE Hardware, that day.

The grey blower air input pipe might create a better suction, if it extended somewhat farther into the exhause section ducting, getting it a little farther out of whatever turbulance is created by the suction port takeoff on the "Y" fitting. That's my hunch. Maybe another six inches or so?

The suction CFM recommended by 4metals is 100 CFM for every 1 square foot of hood door opening. So far, I'm estimating the tests to have shown a venturi suction of about 40% of the blower air CFM. But the cost of a larger blower, so far, seems to be way less than the cost of an acid resistant blower.

That's pretty much it, in a nutshell.

Any other tests and results posted by others, would be greatly appreciated.


----------



## eeTHr

Correction!

When I made the calculations for the area of the gap between the 2" blower air input pipe, and the 3" _*inside*_ diameter of the "Y" fitting, I erroneously used the inside area of the smaller pipe (2") to subtract from the inside area of the larger pipe.

I recalculated it, using the outer diameter of the smaller pipe to figure the gap area, and the cross sectional area of that gap is really only 2.635 square inches. That's less than the inside area of the smaller pipe, which is 3.1415 square inches.

I think that for the total air volume in the exhaust duct to be twice as much as the blower (by combining both the air source from the blower, and the air source from the suction port), and thus making the total air volume in the exhause ducting a balanced 50-50 ratio between the blower air and the suction port air, the gap area would need to be equal or greater than the area of the smaller blower air input pipe.

A 50-50 ratio of the gap and blower pipe inside areas seems technically ideal, but to compensate for air resistance, I think the gap area should actually be somewhat larger (or at least the exhaust ducting following it should be). I haven't tested this yet, and I am basing this only on other tests I made with the other type of venturi configuration, where too much back pressure in the exhaust duct would either reduce the suction, or stop it altogether and cause air to blow out of the suction port instead of sucking in. I searched the Web, but couldn't find any formulas for calculating optimum ratios for the suction effect.

If anybody has any information about this, I would appreciate it if you would please post it.


----------



## eeTHr

I decided to try calculating the gap area using a thinwall schedual 20 pipe for the 2" blower air input. But I don't have a piece of it handy, to measure the wall thickness. So I measured the thickness of the 3" exhaust section thinwall, and used that. The actual thickness of the 2" pipe will be slightly less.

Now, the gap area is 3.091 square inches---less than the 3.1415 gap area with the schedule 40 2" pipe. So that should work for the venturi section, especially since the actual wall thickness of the 2" thinwall is even slightly less than what I used in the computation.

Also, using a schedual 20 "Y" fitting and 3" to 2" reducer, will cost less.

I think that using 4" ducting, after a couple feet of the 3", would be best, especially if there are any turns in the exhaust. I think that the 3" section is going to be necessary, however, to keep from reducing the air speed around the tip of the blower air pipe, as the actual venturi suction will be created there, which will be a few inches into that exhaust section, as mentioned before.

For larger blower pipes, the cross sectional areas will need to be figured and applied accordingly (Area of a circle = pie times radius squared), remembering to use the *outer* diameter of the smaller blower pipe when calculating the gap between the air input pipe and the "Y" fitting.

Edit: Corrected spelling of "decided." Changed wording in paragraph 2 to read "less than the 3.1415 gap area with the schedule 40 2" pipe," for clarity.


----------



## Geo

you may be over thinking it a bit, remember K.I.S.S. keep it simple stupid. if you trade your wet/dry vac for an electric leaf blower you will get more psi on your pressure side. hook it up and if it sucks.


----------



## eeTHr

I already mentioned that as a possible forced air source, and so did someone else.

I tried to get some CFM info on the leaf blowers, but they all list their air flows in MPH! And speed doesn't necessarily indicate volume of flow, you know? Right now, I'm thinking about the two blowers that I mentioned in previous posts, one was 480 CFM for $46.00 and the other was $75.00 with 1400-1550 CFM.

I may be over thinking it, but apparently so far, nobody but shyknee and myself has gotten any indication of getting a venturi to work well enough to achieve the recommended 100 CFM per square foot of hood door opening. So I thought I'd give a rundown of my tests and progress, in case anyone could add some helpful knowledge to it.

And I don't know what could be much simpler than the 3-piece venturi section that also tested out to be the most efficient. do You?

P.S. I did state, several times, that I used the shop vac and small pipes just to test the various configurations. I already had the shop vac, and small pipes are cheaper, especially since I tested different configurations.


----------



## glondor

Keep at it Eethr. I for one would like to see a working system. cheers Mike


----------



## glondor

Keep at it Eethr. I for one would like to see a working system. cheers Mike


----------



## eeTHr

Thanks, glondor.

By the way, I checked the leaf blowers last night, and Home Depot is listing the CFM on almost all of theirs. But none of the electrics go over 385 CFM, and even the gasers don't go over 420. I have noticed that the electrics make lots of noise, too. Maybe it's the mulcher blades?

Also, the 46.00 blower has been discontinued, and I couldn't find anyone that stocks them anymore.

It appears that the company which made them, Lasko, also makes the Stanley branded units, but not in that high of CFM.


Edit: Corrected "to" to "too."


----------



## Geo

i recently acquired a blower that is used to inflate those inflatable party things the kids play in( moon bounce) or whatever its called. im not sure of the cfm but it blows like a hurricane. :lol:


----------



## eeTHr

Geo---

I wish I knew of an inexpensive air flow meter. It would sure help to find out exactly what is happening in a duct system, and for measuring blowers.


----------



## butcher

measuring water coloumb can be done with a clear hose and some water, the pickup for static duct pressure can be made by drilling the holes in the side of some copper tubing, a search on the web should help you build the simple tools.


----------



## qst42know

eeTHr said:


> Geo---
> 
> I wish I knew of an inexpensive air flow meter. It would sure help to find out exactly what is happening in a duct system, and for measuring blowers.



Dwyer vaneometers and manometers can be had fairly cheap on eBay. Should help give some indication of what you are looking for.

http://www.ebay.com/itm/DWYER-480-VANEOMETER-AIR-VELOCITY-METER-NEW-/230586666374?pt=LH_DefaultDomain_0&hash=item35b0094d86


----------



## eeTHr

I found some more blowers, so here's a list of what looks like the best valuse, out of a few dozen that I looked at---

420 CFM, 8", ? Watts, $29.62

435 CFM, 6", 115 Watts, $79.43 (Five year "no hassle" warranty)

440 CFM, 6", ? Watts, $72.28

471 CFM, 8", 54 Watts, $59.25

500 CFM, 8", ? Watts, $31.92

740 CFM, 8", ? Watts, $86.99

1400 to 1575 CFM, 8", 165 Watts, $74.99 (two speed)


----------



## eeTHr

Quest---

I didn't even know what they were called. 8) 

Here is an anemometer on eBay. He says it can measure both volume of flow (CFM) and speed (FPM). But it ain't cheap.

Here's one for $109.99, but it only measures speed.

The swing arm types are less, but again, it's only speed, not CFM.



Edit: Corrected "measure" to "measures."


----------



## eeTHr

I have a hunch that the CFM measurements are going to involve taking a vacuum reading on the venturi intake, and an air speed reading, and some math.

:|



Or maybe just the cross sectional area of the pipe, and the air speed.


----------



## eeTHr

On the blowers links in my previous post, I added the Wattage ratings for the ones that listed it.

The reason is that any backpressure, created by duct restrictions, like too small of diameter pipes, bends, filters, and even just excessive length of ducting (unless it is of a larger diameter), can bog down a motor, depending on how much power it has. Watt is a unit of electrical power, and can be converted to horsepower. 100 Watts = 0.134 horsepower.

All of the blowers that I listed appear to be relatively low power, from 0.072 HP up to 0.22 HP, for the ones that listed either their Amps (at 115 Volts), and I calculated it, or actually listed their Wattage.

So, while the CFMs appear to be high enough for small fume hoods, you might not be able to add a lot of turns or make really long duct runs, without dragging the airflow down, and thus the suction through the venturi and the hood, significantly.

Of course, none of these blowers are acid resistant, so I've listed them only for venturi system use.


Edit: Corrected "watager" to "wattage," in first sentence.


----------



## qst42know

Both a vaneometer and manometers are only simple indicators. They don't give a direct measurement of CFM but they could be useful to indicate if your modifications have actually made an improvement or not.

A vaneometer shows air movement with a weighted poly strip. 

And a manometer is a vacuum difference between two points in your system. Such as the front and back of a filter, or the vacuum in the hood compared to the room.


----------



## eeTHr

Quest---

Ah....Now it's starting to make sense. When I did a search using those names, the sites I looked at seemed to be using them interchangeably, which only confused things for me.

Thanks.


----------



## eeTHr

I just ordered one of the vaneometers from the eBay link provided by qst42know. Very excellent, thanks again.



It looks like the CFM can be easiest calculated using the area of the hood door opening, and the air speed.

The way I see it, the volume of air flow, equals air speed multiplied by the area it's passing through.

(Volume Rate) = (Air Speed) x (Door Area).

So, to find the air speed needed at a hood door opening, it would be---

(Air Speed) = (Volume Rate) divided by (Door Area).

The recommended flow at the hood is 100 CFM for every square foot of door opening area.

The formula to find the required air speed, as measured at the door opening, would be---

AS = VR / DA
FPM = CFM / DA

If you measure the hood door opening area in inches, it would come out---

FPM = 100 / (Width" x Height" / 144)

The 144 just converts the square inches to square feet, so everything will be in the same measuring units.

AS: Air Speed.
VR: Volume Rate.
DA: Door Area.
FPM: Feet Per Minute.
CFM: Cubic Feet per Minute.

Corrections are welcome! 8)


----------



## evL

Hello folks, 

Well thank you all again for a great read, [ the sound of applause in a large hall ]. I realize that my post is over a year late but none the less this 
information was just what I was looking for. And eeTHr , you did a bang up fantastic job. As I was rounding up on page four of this thread and 
heading down it I had a really good idea of what you had found worked the best. I couldn't help but think, "why doesn't he draw it up". And I almost did 
because this sounded just like what I have been mulling over at the shop. 
Then I saw this draft of yours towards the middle :: 

http://img703.imageshack.us/img703/574/suctionventuri7.jpg 

Bingo! Just what I thought. But then came this one from you :: 

http://img819.imageshack.us/img819/589/suctionventuriammentype.jpg 

Perfect!!! We owe you one for your work eeTHr. This has helped me out BIG TIME. I was originally going to run with the first design pic. Like 
I said, I had that in my head at first but thought I'd look into some sort of confirmation to the design. So I went a searching... This Forum and 
the Web. That's when I found this thread, thank goodness. 
I noticed the Ammen pic in the beginning of this thread that jimdoc posted :: 

http://www.goldrefiningforum.com/phpBB3/download/file.php?id=9933&t=1 

I thought it was great. Then spent a quite a while looking into that... You summed it up well with your tests. 

So eeTHr you mentioned, at the end of page five the "gap area" of the 2" in the 3" Wye. I think a 4" Wye could be used as well to compensate for 
that issue. And the point that Geo made was fantastic, "the pressure going in works better at the exhaust end", (page five). Not only a great point 
but would be easy to do if one does like you mentioned further down in the "gap area" post, "using 4" ducting", might pan out quite well if one needed 
to shove that 2" pipe a little more down stream. Ok, I am set. Thanks again folks... 

[ evL ]


----------



## kadriver

Geo said:


> i recently acquired a blower that is used to inflate those inflatable party things the kids play in( moon bounce) or whatever its called. im not sure of the cfm but it blows like a hurricane. :lol:



I have one of those also - got it at the thrift store for $24.99

It is made of bright yellow plastic and really puts out a forceful stream of air.

I was thinking of making a noxx scrubber using it to draw the gas through the scrubber.

kadriver


----------



## Geo

kadriver said:


> Geo said:
> 
> 
> 
> i recently acquired a blower that is used to inflate those inflatable party things the kids play in( moon bounce) or whatever its called. im not sure of the cfm but it blows like a hurricane. :lol:
> 
> 
> 
> 
> I have one of those also - got it at the thrift store for $24.99
> 
> It is made of bright yellow plastic and really puts out a forceful stream of air.
> 
> I was thinking of making a noxx scrubber using it to draw the gas through the scrubber.
> 
> kadriver
Click to expand...


yep, thats what mine looks like. all plastic parts. right now im using a plastic tub upside down with a good vacuum cleaner as vacuum. i am slowly gathering material for a decent workspace and fumehood. as it is right now, im working outside which is a pain when it rains or is freezing. i have some very good material and i know its worth well enough to pay for the remaining material and even pay someone to construct it. if i just had someone who knew how to refine it for me right here, id be in business.


----------



## scrappile

I have a Kurz 1440 , if you need to do some testing when building your hood, just pickup shipping , :lol:


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## Cap1

It is my opinion that using a venturi method of air extraction is far superior than using an inline suction pump at the exhaust end. You eliminate the need to replace the inline pump every 2-3 years from corrosion damage, even if the pump is insulated. Although you do seem to have a bigger than average enclosure box. Maybe you should think about scaling down your box to only 1 exit port and get the system working. Then increase the size of the box along with the piping. You could use temporary side panels to make the box smaller and then remove each panel as the box gets bigger yet still working.


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## DJPGold

evL said:


> Hello folks,
> 
> Well thank you all again for a great read, [ the sound of applause in a large hall ]. I realize that my post is over a year late but none the less this
> information was just what I was looking for. And eeTHr , you did a bang up fantastic job. As I was rounding up on page four of this thread and
> heading down it I had a really good idea of what you had found worked the best. I couldn't help but think, "why doesn't he draw it up". And I almost did
> because this sounded just like what I have been mulling over at the shop.
> Then I saw this draft of yours towards the middle ::
> 
> http://img703.imageshack.us/img703/574/suctionventuri7.jpg
> 
> Bingo! Just what I thought. But then came this one from you ::
> 
> http://img819.imageshack.us/img819/589/suctionventuriammentype.jpg
> 
> Perfect!!! We owe you one for your work eeTHr. This has helped me out BIG TIME. I was originally going to run with the first design pic. Like
> I said, I had that in my head at first but thought I'd look into some sort of confirmation to the design. So I went a searching... This Forum and
> the Web. That's when I found this thread, thank goodness.
> I noticed the Ammen pic in the beginning of this thread that jimdoc posted ::
> 
> http://www.goldrefiningforum.com/phpBB3/download/file.php?id=9933&t=1
> 
> I thought it was great. Then spent a quite a while looking into that... You summed it up well with your tests.
> 
> So eeTHr you mentioned, at the end of page five the "gap area" of the 2" in the 3" Wye. I think a 4" Wye could be used as well to compensate for
> that issue. And the point that Geo made was fantastic, "the pressure going in works better at the exhaust end", (page five). Not only a great point
> but would be easy to do if one does like you mentioned further down in the "gap area" post, "using 4" ducting", might pan out quite well if one needed
> to shove that 2" pipe a little more down stream. Ok, I am set. Thanks again folks...
> 
> [ evL ]


Nearly 10 years later. I’ve just finished reading these 6 pages, and I feel as if everyone understands it better except me  the diagram links are broken, could someone please fix them if possible before I have to bust out the pencil and paper to see if understand the system correctly


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## FrugalRefiner

I was able to fix a few links, but probably not the ones you wanted. eeTHr had posted a lot of links to images on ImageShack, but the images are no longer there. eeTHr hasn't been here since 2014.

Dave


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## DJPGold

FrugalRefiner said:


> I was able to fix a few links, but probably not the ones you wanted. eeTHr had posted a lot of links to images on ImageShack, but the images are no longer there. eeTHr hasn't been here since 2014.
> 
> Dave


No worries, thank you. I was hoping at the end of this thread there would be a conclusion on what works for the Venturi/eductor exhaust but yeah no luck. I think I’ll take this design from Kurtak and hope it works


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## FrugalRefiner

Take a look in The Library. There are a few threads on hoods, ducting, and scrubbers.

Dave


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## DJPGold

Hopefully anyone who has experience with Venturi fume hoods can help me out here I’m wondering if I would get away with shortening the air input tube from 1m to a couple hundred mm without a negative effect. My thinking is that it would decrease drag and improve the blower force closer to the output. 

The red line marks roughly where the tube ends, and green marks the section I would like to cut.


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## Yggdrasil

DJPGold said:


> Hopefully anyone who has experience with Venturi fume hoods can help me out here I’m wondering if I would get away with shortening the air input tube from 1m to a couple hundred mm without a negative effect. My thinking is that it would decrease drag and improve the blower force closer to the output.
> 
> The red line marks roughly where the tube ends, and green marks the section I would like to cut.


I can't see a problem with that.
For performance the only important thing is the speed increase through the actual venturi and a pressure drop "Vacuum" just after,
when the speed goes back to normal. But I think the red line needs some more space to be effective.
You can clearly see the different diameters.
And the output end should have as little restrictions as possible.


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## kurtak

DJPGold said:


> Hopefully anyone who has experience with Venturi fume hoods can help me out here I’m wondering if I would get away with shortening the air input tube from 1m to a couple hundred mm without a negative effect. My thinking is that it would decrease drag and improve the blower force closer to the output.
> 
> The red line marks roughly where the tube ends, and green marks the section I would like to cut.


First of DJPGold - could you please keep ALL of your questions concerning building a fume hood in ONE thread

Mods - could one of you please combine ether this thread with his other thread - or - the other thread with this one

the other thread is ------------









Fume hood venturi.


Hello folks, Well thank you all again for a great read, [ the sound of applause in a large hall ]. I realize that my post is over a year late but none the less this information was just what I was looking for. And eeTHr , you did a bang up fantastic job. As I was rounding up on page four of...




goldrefiningforum.com





IMO - this one should be combined with the link above as the link above is already a longer & more in depth discussion about fume hoods which in turn takes other members to a more detailed discussion as we move forward in fume hood discussion to help answer DJPGold's questions

Edit to add; - Once the threads are combined I will "try" to answer/help DJPGold --- I say "try" because I am quite busy at the moment so just not sure if &/or how much time I can provide here 

Kurt


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## kurtak

DJPGold said:


> Hopefully anyone who has experience with Venturi fume hoods can help me out here I’m wondering if I would get away with shortening the air input tube from 1m to a couple hundred mm without a negative effect. My thinking is that it would decrease drag and improve the blower force closer to the output.
> 
> The red line marks roughly where the tube ends, and green marks the section I would like to cut.


Short answer - that is going to depend A LOT on the rest of your system set up ????

To be discussed once the two threads are combined

Kurt


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## Yggdrasil

kurtak said:


> First of DJPGold - could you please keep ALL of your questions concerning building a fume hood in ONE thread
> 
> Mods - could one of you please combine ether this thread with his other thread - or - the other thread with this one
> 
> the other thread is ------------
> 
> 
> 
> 
> 
> 
> 
> 
> 
> Fume hood venturi.
> 
> 
> Hello folks, Well thank you all again for a great read, [ the sound of applause in a large hall ]. I realize that my post is over a year late but none the less this information was just what I was looking for. And eeTHr , you did a bang up fantastic job. As I was rounding up on page four of...
> 
> 
> 
> 
> goldrefiningforum.com
> 
> 
> 
> 
> 
> IMO - this one should be combined with the link above as the link above is already a longer & more in depth discussion about fume hoods which in turn takes other members to a more detailed discussion as we move forward in fume hood discussion to help answer DJPGold's questions
> 
> Edit to add; - Once the threads are combined I will "try" to answer/help DJPGold --- I say "try" because I am quite busy at the moment so just not sure if &/or how much time I can provide here
> 
> Kurt


Done now.
Frankly I did not see that it was a new thread.


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## kurtak

DJPGold said:


> I think I’ll take this design from Kurtak and hope it works


That was my first build which though yes it did work it did not work near as well as I wanted so there where changes made to it to make it more effective

I am quite busy right now but will try to explain *if*/when I get time

Kurt


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## DJPGold

kurtak said:


> That was my first build which though yes it did work it did not work near as well as I wanted so there where changes made to it to make it more effective
> 
> I am quite busy right now but will try to explain *if*/when I get time
> 
> Kurt


No rush mate, you do what you’ve gotta do.
Apologies for creating a new thread, I didn’t want to “hijack” the previous but now I realise that’s sort of the whole point of a community forum 

I’m keen to hear/see the improvements you made. My exhaust run has two 90° degree bends before the end of the run, atm I’ve got two 45° couplings so the bend is smoother, I haven’t yet finished the run. The blower that I used wasn’t strong enough for me to be happy so I’m getting a new one anyway, I will uploaded relevant pictures and videos later today


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## DJPGold

DJPGold said:


> No rush mate, you do what you’ve gotta do.
> Apologies for creating a new thread, I didn’t want to “hijack” the previous but now I realise that’s sort of the whole point of a community forum
> 
> I’m keen to hear/see the improvements you made. My exhaust run has two 90° degree bends before the end of the run, atm I’ve got two 45° couplings so the bend is smoother, I haven’t yet finished the run. The blower that I used wasn’t strong enough for me to be happy so I’m getting a new one anyway, I will uploaded relevant pictures and videos later today


Hopefully the blower I get will have enough power to work as well as I need. There’s a couple bends in this one and it’s not a long run before the bends either


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## kaisernine

Anyone doing this, especially in a residential home/basement ( either not recommended ) should probably have a second blower ready to go with some type of quick connect and alternative power source ( in the case power gets interrupted ) - just a friendly suggestion - this stuff can go south fast.

lots of people try to do refining safely in the now - without looking at the issues that can arise in the future - don't rush refining and it won't rush you.


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## stoneware

What do chimneys and smelter stacks have in common, neither require electricity to operate,

I believe a similar stack could be used to evacuate a fume hood.

The mound leading up to the smelter stack is a tunnel from a lower elevation.


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## Yggdrasil

stoneware said:


> What do chimneys and smelter stacks have in common, neither require electricity to operate,
> 
> I believe a similar stack could be used to evacuate a fume hood.
> 
> The mound leading up to the smelter stack is a tunnel from a lower elevation.
> 
> View attachment 53236


That depends entirely on temperature differences and height.
If you get the chimney interior hot enough over sufficient length, it will generate its own draft.

But it must be high enough and be kept at high enough temperature over the time it is used, which will cost energy of some kind.

So I believe that in real life applications of today, fans will probably be the easiest solution.


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## stoneware

Yggdrasil said:


> That depends entirely on temperature differences and height.
> If you get the chimney interior hot enough over sufficient length, it will generate its own draft.
> 
> But it must be high enough and be kept at high enough temperature over the time it is used, which will cost energy of some kind.
> 
> So I believe that in real life applications of today, fans will probably be the easiest solution.


Most people who own an older house with a fireplace will block them off from the room.

Even a fireplace without fire in the hearth will create its own draft from warm air in the room.

If you've ever been in an old mine shaft the air leaving the portal is very strong breeze.

Fume hoods create warm air, so why not go with natural convection.


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## Yggdrasil

stoneware said:


> Most people who own an older house with a fireplace will block them off from the room.
> 
> Even a fireplace without fire in the hearth will create its own draft from warm air in the room.
> 
> If you've ever been in an old mine shaft the air leaving the portal is very strong breeze.
> 
> Fume hoods create warm air, so why not go with natural convection.


First and foremost because it do not like obstacles and any scrubbing action will be an obstacle


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## DJPGold

kaisernine said:


> Anyone doing this, especially in a residential home/basement ( either not recommended ) should probably have a second blower ready to go with some type of quick connect and alternative power source ( in the case power gets interrupted ) - just a friendly suggestion - this stuff can go south fast.
> 
> lots of people try to do refining safely in the now - without looking at the issues that can arise in the future - don't rush refining and it won't rush you.


I was thinking of either buying an identical blower that can be powered by a UPS, or make a quick connect port for my leaf blower that I can slap in


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## Edlin

DJPGold said:


> No worries, thank you. I was hoping at the end of this thread there would be a conclusion on what works for the Venturi/eductor exhaust but yeah no luck. I think I’ll take this design from Kurtak and hope it works


Theoretically as long as the smaller diameter pipe extends past the wye it should still work


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## dannlee

They can tweak this design to pull a near-perfect vacuum (deafeningly loud!) or move high volumes of liquids with a small pump...

(
(Apologies I can't attribute the source of this image, kinda stolen off the NET a long time ago as a cheat sheet for my fume hood)


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