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OfflineTheHenderson
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Registered: 12/30/21
Posts: 28
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Laminar flow hood question
    #27765738 - 05/06/22 09:58 AM (2 years, 8 months ago)

Ive read the main guides on here, which are super helpful as I plan to build a flow hood in the next couple months.

The one thing I haven't seen adressed is that it appears those very thick filters are always used, but an h14 grade filter must meet the 99.997 requirement so I fail to understand why people aren't using the much easier to find, far cheaper commenly available filters that meet the official standards. Can someone explain why?

All I can think of is it would need to be changed . more often along with likely needing more airflow. Used blowers are cheap and available though, I assume tons of them would be powerful enough, so I feel like I'm missing something.

Also any recommendations on where to get the regular thick filters commonly used?

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InvisibleMycoManna

Registered: 05/06/22
Posts: 3
Loc: US
Re: Laminar flow hood question [Re: TheHenderson]
    #27765866 - 05/06/22 11:44 AM (2 years, 8 months ago)

I joined the forum for this exact question. I’m designing/building a ventilation system for a clean room though. Spent the last several days learning WAY more about air filtration than I ever cared to. It’s like, all relevant information about air filtration has been diluted by the booming Covid Air-Purifier market.


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InvisibleMycoManna

Registered: 05/06/22
Posts: 3
Loc: US
Re: Laminar flow hood question [Re: MycoManna]
    #27767180 - 05/07/22 10:25 AM (2 years, 8 months ago)

Henderson, I’m pretty new. I’ve had the same nagging question. I found a Filtrete that’s advertised as “True HEPA” touting “…can remove 99.97% of all airborne particles that pass through the filter…” and includes the legal disclaimer “as small as 0.3 microns from the air passing through the filter media. Initial efficiency value.”

Supposedly it’s a new product. Designed for Filtrete’s air purifiers. It’s a smaller filter, approx 16”x10”x2”. I submitted a question to Filtrete, asking what the MERV classification would be for this filter, or at a minimum the HEPA rating. Unless I hear back from Filtrete that it has a MERV of less than 17, I plan on using it (two, side by side) to scrub my 96 square foot clean room/tent. I’m going to do some sterile transfers with pucks this weekend. Some strains that I’m not too worried about. We’ll see if it comes out contaminated I guess.


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OfflinePBJ710
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Registered: 07/05/19
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Re: Laminar flow hood question [Re: MycoManna]
    #27767223 - 05/07/22 10:59 AM (2 years, 8 months ago)

The big thing you are both missing is the LAMINAR FLOW part.  Just because it has the word HEPA on it, doesn't mean that it's suitable for our purposes as it would create turbulent airflow that would unpredictably kick up contaminants into your work area. 

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Invisiblesandman420
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Registered: 06/17/04
Posts: 5,387
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Re: Laminar flow hood question [Re: PBJ710]
    #27767788 - 05/07/22 07:48 PM (2 years, 8 months ago)

Yes the filter needs a high pressure drop (at least 0.4" w.g. at 90fpm) in order to get good laminar flow. The room hepas and furnace filters have really low pressure drop because they are intended for high velocity airflow.


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InvisibleBoozie
I like beer.
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Registered: 02/18/10
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Re: Laminar flow hood question [Re: sandman420]
    #27767907 - 05/07/22 09:29 PM (2 years, 8 months ago)

Quote:

PBJ710 said:
The big thing you are both missing is the LAMINAR FLOW part.  Just because it has the word HEPA on it, doesn't mean that it's suitable for our purposes as it would create turbulent airflow that would unpredictably kick up contaminants into your work area. 



Quote:

sandman420 said:
Yes the filter needs a high pressure drop (at least 0.4" w.g. at 90fpm) in order to get good laminar flow. The room hepas and furnace filters have really low pressure drop because they are intended for high velocity airflow.




:whathesaid: …or rather, what they said.

You want something like this:



Not this:



Huge difference.


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"After silence, that which comes nearest to expressing the inexpressible is music." - Aldous Huxley


   

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InvisibleBoozie
I like beer.
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Registered: 02/18/10
Posts: 1,227
Loc: :ↄo⅃
Re: Laminar flow hood question [Re: MycoManna]
    #27767932 - 05/07/22 09:46 PM (2 years, 8 months ago)

Your fan/airflow plays just as big of a role though too, in order to create the laminar flow.

Best way I can describe is go to your kitchen sink, open that faucet all the way. Water just pissing out, almost foaming with air at the tap, right? Now dial it back slowly until you have just one, smooth stream, barely pouring from the spigot. Zero disturbance. That’s laminar flow.


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"After silence, that which comes nearest to expressing the inexpressible is music." - Aldous Huxley


   

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