# ventilator fume hood



## Slochteren (Oct 25, 2015)

Hi,

im building a fume hood and have a ventilator laying arround wich has an capacity off 440 m3/hour, is that enough or do i need one with more volume?
i use this design: http://goldrefiningforum.com/phpBB3/viewtopic.php?f=40&t=19965#p205097

thx 

Paul


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## 4metals (Oct 25, 2015)

Do you have a corrosion resistant blower or is it plain steel? You are pulling enough air (260 CFM) to exhaust enough air out of a conventional hood with an open area of 0.24 square meters. (2.6 sq ft)

The hood in the thread is using a venturi because the blower will not resist the corrosivity of the fumes. A venturi induces a vacuum and loses efficiency, meaning the total airflow through the venturi does not draw a suction flow equal to the input, so I would say it is too small.


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## rickbb (Oct 26, 2015)

From what I've read you need 100 CFM for every 1 square foot of opening in your hood. So if you have a hood with 1 foot high by 3 foot wide opening, (3 square feet). You would need an exhaust rate of 300 CFM. I'd up that by 10 or 20 % to play it safe.

You have to account for every bend, elbow and total running length of the piping out as that all reduces the efficiency of the rating of what ever vacuum you use. Venturi's will make a non-corrosive protected blower a good vacuum, but will lose quite a bit of the rating off blower.


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## Slochteren (Oct 29, 2015)

Thank you for the advise, i have another blower laying arround http://www.walmart.com/ip/B-Air-Blower-KP-680-Koala-Power-1-2-HP-447-CFM-Inflatable-Blower/30855253 It is only 110 volt so i need the get me a transformer from 220V to 110V. But before getting such a transformer i would like to know if this blower is strong enough for a venturi based fume hood.

Paul


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## Smack (Oct 30, 2015)

You might be able to change the wires on the motor to the 220v positions if equipped.


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## saadat68 (Jan 2, 2017)

rickbb said:


> From what I've read you need 100 CFM for every 1 square foot of opening in your hood. So if you have a hood with 1 foot high by 3 foot wide opening, (3 square feet). You would need an exhaust rate of 300 CFM. I'd up that by 10 or 20 % to play it safe.
> 
> You have to account for every bend, elbow and total running length of the piping out as that all reduces the efficiency of the rating of what ever vacuum you use. Venturi's will make a non-corrosive protected blower a good vacuum, but will lose quite a bit of the rating off blower.





4metals said:


> Do you have a corrosion resistant blower or is it plain steel? You are pulling enough air (260 CFM) to exhaust enough air out of a conventional hood with an open area of 0.24 square meters. (2.6 sq ft)
> 
> The hood in the thread is using a venturi because the blower will not resist the corrosivity of the fumes. A venturi induces a vacuum and loses efficiency, meaning the total airflow through the venturi does not draw a suction flow equal to the input, so I would say it is too small.




Hi
Opening of my *venturi *hood is 1 square foot. Is 100 CFM blower enough?


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## rickbb (Jan 4, 2017)

saadat68 said:


> Hi
> Opening of my *venturi *hood is 1 square foot. Is 100 CFM blower enough?



The CFM draw is measured at the working opening of the hood. There are calculations to make for all the bends and restrictions of a venturi system to take into account. They all reduce the blowers rating when you get down to the actual opening of the fume hood. 

A single square foot opening it kind of small to be working in with both hands, moving vessels of liquids and such in and out of. Not sure I understand.


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## saadat68 (Jan 4, 2017)

rickbb said:


> saadat68 said:
> 
> 
> > Hi
> ...



Thanks. My work shop and my business is small now and maybe I will make a bigger hood in future.
But my question is:
*
we need 100 CFM for every 1 square foot of opening in your hood.

Is this rule for blower or educator ? In other words we need 100 CFM blower or 100 CFM educator for every 1 square foot of opening in your hood ?*


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## 4metals (Jan 4, 2017)

I think a combination of your English and the fact that you are making things more complicated for yourself. Please use 1 thread to get your answer. You are asking in a thread about a hood and a thread about a scrubber and confusing the two. 

You do need 100 CFM for every square foot of opening. That is different from the Blower CFM if using that blower to cause a suction by venturi action. I answered this earlier on another thread, please stop jumping around.

Even if your quantity of work is small now, there is a minimum size you should be able to process in a hood. I would say that the ability to handle a 4 liter beaker inside of a hood should be a minimum. That would make a hood with an opening 1 square foot too small. I would think 2 feet wide by 1.5 feet high (or 3 sq ft) would be a good size or 1.5 feet by 1.5 feet at a minimum. (2.25 sq ft) 

Remember you need to hold a beaker with 2 hands and place it in the hood, you will cause yourself more problems by making it too small in the beginning.


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## saadat68 (Jan 4, 2017)

4metals said:


> I think a combination of your English and the fact that you are making things more complicated for yourself. Please use 1 thread to get your answer. You are asking in a thread about a hood and a thread about a scrubber and confusing the two.
> 
> You do need 100 CFM for every square foot of opening. That is different from the Blower CFM if using that blower to cause a suction by venturi action. I answered this earlier on another thread, please stop jumping around.
> 
> ...


OK and sorry for double posting 
Thank you. I never think making a scrubber and hood can have these problems and intricacy  
can you say how many CFM blower need for every square foot of opening? ( Yes you said it is impossible but just an example can help me to have a view of that)


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## rickbb (Jan 5, 2017)

Lets try again, you need a minimum of 100CFM for every square foot of opening. Notice the word "opening". That's what counts, not the blower rating or the vacuum pump rating. 

The fume hood "opening" where you stick your hands in to work, the "opening" of the scrubber where it sucks in the air you want to scrub is what determines the starting point is sizing you blower/vacuum pump. 

All of the pipe/duct work, bends, venturis, drawing your gasses under fluids for scrubbing and so forth reduce the flow rate so you want to oversize the blower/pump to accommodate for all of that to meet the "opening's", (there's that word again), requirements.

Vacuum pumps for scrubbers need to be size according to the various columns of fluid the gasses will be sucked through. Columns of liquid, several feet tall will require a very strong pump to bubble the gasses though.


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## saadat68 (Jan 6, 2017)

Thanks
I will make hood from 4metals design. It is 500 CFM
http://goldrefiningforum.com/~goldrefi/phpBB3/viewtopic.php?f=40&t=19965&p=264875#p264875


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