Fume hood venturi.

[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]

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]

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]

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

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:

 

[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.