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Offlineast
newbie
Registered: 05/26/02
Posts: 38
Last seen: 21 years, 7 months
flow hood
    #736717 - 07/10/02 12:04 PM (21 years, 9 months ago)

im attempting to build the flow hood from this link:

http://www.theforestfloor.org/archives/main/Flowhood_DIY.html

I have a 400cfm blower that I got from a hydroponics shop awhile ago that i never used.. Would 400cfm be enough for the 24x12x5.8 screen it says you need at least one that is 90cfm higher then the one I got..

but would 400cfm still do the job?

thanks

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OfflineDinoMyc
Ipsa scientiapotestas est
Registered: 11/13/99
Posts: 1,080
Last seen: 17 years, 10 months
Re: flow hood [Re: ast]
    #737478 - 07/10/02 05:38 PM (21 years, 9 months ago)

I don't have any general formulas on hand, but you want to ensure enough laminar flow to produce the sterile environment you desire. Look it all up in GGMM and TMC (staments, chilton)


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If I made affront, I apologize.
If I made affirmation, I apologize.
I merely came to listen, came to say.

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OfflineMaveric2112
journeyman
Registered: 07/09/02
Posts: 83
Loc: My name is God so there f...
Last seen: 21 years, 7 months
Re: flow hood [Re: ast]
    #737530 - 07/10/02 06:00 PM (21 years, 9 months ago)

What is the size of the room you are using?


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Ahh what the hell am I talking about? I just like to make up stories. In short, I'm full of Sh$t!!!!!!

Edited by Maveric2112 (07/10/02 06:01 PM)

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Offlinemodulo
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Registered: 10/04/00
Posts: 4
Loc: Califor-nai-yay
Last seen: 21 years, 8 months
Re: flow hood [Re: ast]
    #743538 - 07/13/02 10:04 AM (21 years, 9 months ago)

Think of it this way - 400 cubic feet per minute, that could equal a 10x10x4 ft. closet. You would be exchanging the air in there once every minute. I'm guessing that the size of your hood is nowhere nearly as large, perhaps only half that size? maybe even 1/4? Atleast, based on the flowhoods in the labs I've worked in, I haven't seen one that large quite yet without earning the term "clean-room". So you're essentially going to be replacing the air 4 or 5 times every minute.

The question at this point is no longer if it is big enough, but can your filtration system keep up with it? When moving that much air you have to be sure that your hepa (or whatever system) is capable of filtering/buffering enough clean air to lower your particulates to a good level.

Now an even bigger question - what is a good particulate level for your project?

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Offlineast
newbie
Registered: 05/26/02
Posts: 38
Last seen: 21 years, 7 months
Re: flow hood [Re: modulo]
    #743840 - 07/13/02 01:41 PM (21 years, 9 months ago)

im not building a clean room... im building the box in the link at the top.. it says you need a 490cfm+ im using the 400cfm as i said... im just wondering if it would be enough to do grain transfers and inoculate jars infront of..

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Offlinemodulo
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Registered: 10/04/00
Posts: 4
Loc: Califor-nai-yay
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Re: flow hood [Re: ast]
    #744376 - 07/13/02 07:48 PM (21 years, 9 months ago)

I should have noticed that link...

Anyhow, I think 400cfm is quite a bit. It's probably much more than you need for that project in regards to grain transfers and sterile agar. I've never really felt too much of a wind current when working in flow hoods as they've been pretty wide open.

Go for it. It looks like it will work with 400cfm. Be sure to post results :-)

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OfflineAnnoA
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Registered: 06/17/99
Posts: 24,166
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Re: flow hood [Re: ast]
    #744395 - 07/13/02 08:08 PM (21 years, 9 months ago)

The air velocity from the flow hood should be 100 feet per minute.

Your filter is has an area of 2 square feet.

Means, you need a blower that is capable of delivering 200 cubic feet air per minute at the static pressure of the filter, which is in general 1 inch water column+ around 0.5 inch for the pre filter..

>You will need at least a 495 cfm blower

These 495 refer to the blower delivering air without the static pressure of the filter.
When you mount it behind the filter, it will deliver much less air, namely something around the required 200 cfm.

Unfortunately there is no way knowing how much a blower delivers at a certain static pressure without measuring it.

Luckily though most fans come with a chart that shows the dependance of air flow versus static pressure.

Edited by Anno (07/13/02 08:14 PM)

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Invisiblecontaman
journeyman
Registered: 05/27/02
Posts: 53
Re: flow hood [Re: Anno]
    #744804 - 07/14/02 04:32 AM (21 years, 9 months ago)

I was under the impression that the pre filter went behind the blower(filtering air before it gets to the blower). Is this correct? And I also thought that the pre-filter was not necessary? Now if the prefilter actually attaches to the HEPA(between the blower and HEPA), that will be easier to fit into my construction plans, but will screw up my calculations for the necessary blower...

I have searched google and have not come up with much info regarding flow hoods. Could someone direct me to some good reference(s) regarding flowhoods?

Edited by Olgualion (07/14/02 04:29 PM)

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InvisibleUna
controlleddemolition

Registered: 03/01/01
Posts: 970
Re: flow hood [Re: contaman]
    #744844 - 07/14/02 05:09 AM (21 years, 9 months ago)

It's best to put the prefilter BEFORE the blower because air has a lower resistance when sucked through a filter than blown through a filter. Like this:



If you want to blow it thorugh the prefilter you would need a much stronger blower.
A pre filter isn't necessary but will greatly extend the life of your HEPA filter.

Here are some links to info about professional flowhoods.

http://www.ductless.com/laminar-intro.htm

http://www.envirco.com/nonflash/nflaminar.html

http://www.misonix.com/lfws.htm

http://www.labcaire.co.uk/laminar.htm

http://lab.escoglobal.com/esco_horizontal_laminar_flow_c.htm

http://web.uvic.ca/ohs/laminarflowbsc.html

http://www.cleanairbv.nl/




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Offlineggordon
Stranger
Registered: 06/17/02
Posts: 17
Last seen: 18 years, 6 months
Re: flow hood [Re: ast]
    #746089 - 07/14/02 05:41 PM (21 years, 9 months ago)

I hate to do this but there is no way I will be picking one up There are 2 different Government surplus flow hoods on ebay right now for cheap cheap. The problem I have is that the shipping would cost more than the flowhood. I am pretty sure the guy has quite a few. Just type in "flow hood" in the search and whoever picks them up, you lucky sod! The company selling is in Colorado.

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Anonymous

Re: flow hood [Re: Anno]
    #747388 - 07/15/02 07:02 AM (21 years, 9 months ago)

perhaps you could use one of those air flow booster things...i was rummaging around in the shed and found two of them. These are Robin Hood brand and they say they increase air flow by 200-250 cfm. i think you place them between the fan and the hepa.

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InvisibleUna
controlleddemolition

Registered: 03/01/01
Posts: 970
Re: flow hood [Re: Una]
    #749997 - 07/16/02 04:41 AM (21 years, 9 months ago)

actually more like this:



--------------------
www.911blogger.com

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