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wingover
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Registered: 01/08/17
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FLOW Hoods - couple of questions
#23991936 - 01/08/17 09:42 AM (7 years, 22 days ago) |
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Hi folks, am about to build a horizontal LFH. I've been through many of the threads but still have a couple of questions.
The first relates to plenum pressure. Standard advice is to design for 250 Pa at 0.5 m/s. However, most modern filters sold for use with professional LFHs seem to produce much lower pressures and, with limited choices in the UK, I'm struggling to find one that's close to 250; eg. this H14 grade 18x24 filter (UMPW78_1824) is rated 110 Pa at 0.5 m/s – UMPW78_1824. However I would have thought that, using this filter, the laminar flow should be ok because it's specifically designed for use with an LFH. A lower bp means a less expensive blower, so would be preferable if it works. I guess 110 Pa is also more difficult to manufacture than 250 Pa, so there must be good reason for producing units with lower pressure. Am I missing something, would laminar flow still be better with a 250Pa filter? Thanks.
Second question relates to the hood. I'm successfully using a box but need to increase my work area. I notice that most people use HEPA filters without a hood fitted, but doesn't this cause rotor around top and sides of the flow, with mixing of air reducing the volume of sterile workspace? Would have thought that enclosing the flow in a hood, like most professional systems, eliminates this issue. Sides/top of the hood may generate drag but the resulting turbulence would be no more than from a solid work top when using filter only (and good downstream sterile procedures should minimise the impact). More importantly, there's no mixing with contaminated air from the room until flow approaches the exit. So, in theory, I would expect a hood to provide a greater volume of sterile workspace. Can see the convenience of working without a hood but, in practice, how much does a filter-only solution affect the usable volume and, with no barriers in place, how frequently does a momentary lapse of concentration (eg. moving a dish outside of the airflow) result in contamination? Any feedback greatly appreciated – am not sure which way to go.
Thanks for your help.
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wingover
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Re: FLOW Hoods - couple of questions [Re: wingover]
#24000591 - 01/11/17 09:20 AM (7 years, 19 days ago) |
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For information, the manufacturer of the filter linked above (UMPW78_1824) says it will have no problem producing good laminar flow with 110Pa at 0.5 m/s. It's a bit pricey but, in compensation, the lower back pressure should mean some savings on the blower. With a less powerful blower the whole thing can be made a little smaller and with less noise too.
So, that just leaves the hood question. Do you think my comments are correct and a hood would give increased workspace? Has anyone tried using a laminar HEPA both with and without a hood? Would love to hear from people with experience of LFHs.
Edited by wingover (01/11/17 09:45 AM)
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wingover
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Re: FLOW Hoods - couple of questions [Re: wingover]
#24036329 - 01/24/17 03:17 PM (7 years, 6 days ago) |
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Any takers on the hood issue? Would be great to hear from anyone with experience of filters with and without hoods. In your experience, do you think they provide an advantage or are they just not worth it.
Thanks again.
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spore-ty



Registered: 01/21/16
Posts: 1,028
Loc: In the bush
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Re: FLOW Hoods - couple of questions [Re: wingover]
#24036605 - 01/24/17 04:54 PM (7 years, 6 days ago) |
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Well taking any exposed nutritious material outside of the lamina flow of course will result in contamination.
And to your last post it all depends on why and how much your gonna use it ive decided im gonna use my sab a lot might as well get comfy and get something ive. always wanted
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99.99
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Re: FLOW Hoods - couple of questions [Re: spore-ty]
#24036975 - 01/24/17 06:56 PM (7 years, 6 days ago) |
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My first flow hoods were vertical I never had very good success with them my last one is horizontal and I get a lot less contaminate from it, but if you look up the manual it says horizontal for sterility and vertical for computer work and dust free environments
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bodhisatta 
Smurf real estate agent


Registered: 04/30/13
Posts: 61,889
Loc: Milky way
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Re: FLOW Hoods - couple of questions [Re: 99.99]
#24036988 - 01/24/17 07:01 PM (7 years, 6 days ago) |
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I personally would build a flow hood but for some reason this hobby is filled with flow cabinets
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spore-ty



Registered: 01/21/16
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Re: FLOW Hoods - couple of questions [Re: bodhisatta]
#24037020 - 01/24/17 07:15 PM (7 years, 6 days ago) |
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Bod would you prefer this rather than the flow cabinets? Also Bod is a flow a cabinet not a proper tool for this hobby?
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bodhisatta 
Smurf real estate agent


Registered: 04/30/13
Posts: 61,889
Loc: Milky way
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Re: FLOW Hoods - couple of questions [Re: spore-ty]
#24037035 - 01/24/17 07:22 PM (7 years, 6 days ago) |
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Any cabinet can have a hood made for it. People use cabinets with great success
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bodhisatta 
Smurf real estate agent


Registered: 04/30/13
Posts: 61,889
Loc: Milky way
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Re: FLOW Hoods - couple of questions [Re: bodhisatta]
#24037039 - 01/24/17 07:23 PM (7 years, 6 days ago) |
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Id put some water in the jar with the swabs. I'd worry they're not sterilized since they're only in contact with hot air likely.
Water makes 1700 volumes of steam so it would only take a few drops in the jar to fill it with steam. During the cycle
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spore-ty



Registered: 01/21/16
Posts: 1,028
Loc: In the bush
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Re: FLOW Hoods - couple of questions [Re: bodhisatta]
#24037069 - 01/24/17 07:30 PM (7 years, 6 days ago) |
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Quote:
bodhisatta said: Any cabinet can have a hood made for it. People use cabinets with great success
So the difference between the two is that the hood actually has a design to direct laminar flow and keep other air borne contams out? And of course the other difference is that the filter will basically be enclosed rather flush on the perimeter of the box
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bodhisatta 
Smurf real estate agent


Registered: 04/30/13
Posts: 61,889
Loc: Milky way
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Re: FLOW Hoods - couple of questions [Re: bodhisatta]
#24037618 - 01/25/17 12:25 AM (7 years, 5 days ago) |
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Quote:
bodhisatta said: Id put some water in the jar with the swabs. I'd worry they're not sterilized since they're only in contact with hot air likely.
Water makes 1700 volumes of steam so it would only take a few drops in the jar to fill it with steam. During the cycle
wrong forum, lol fuck
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wingover
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Re: FLOW Hoods - couple of questions [Re: bodhisatta]
#24037827 - 01/25/17 05:51 AM (7 years, 5 days ago) |
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Thanks everyone for your replies, sounds like a hood around the filter would be better.
I've also had another conversation with filter suppliers (wanted to get an unbiased view from users first) and they say the same, a hood prevents en-trained unfiltered air from reducing the aseptic area. This means that a smaller filter can be used to produce the same volume of sterile workspace.
Decision made, I'm fitting a hood!
Many thanks.
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spore-ty



Registered: 01/21/16
Posts: 1,028
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Re: FLOW Hoods - couple of questions [Re: wingover]
#24038229 - 01/25/17 10:01 AM (7 years, 5 days ago) |
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You'll have as much space as big as your filter gets and goodluck and keep us updated !
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wingover
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Last seen: 6 years, 10 months
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Re: FLOW Hoods - couple of questions [Re: spore-ty]
#24039048 - 01/25/17 03:56 PM (7 years, 5 days ago) |
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Will do.
Want to make sure that the whole thing can be easily disassembled and packed away when not required. The lower filter pressure means an in-line pump should be fine and these tend to be less expensive and quieter than squirrels. Can then connect the pump to the (smaller) plenum with a short length of flexible ducting so that the pump, filter/plenum and hood can be disconnected and stored separately.
Also, an 18" x 24" filter with simple hood on all sides could, when required, simply be turned sideways for a full 2' vertical workspace - which might be useful at times.
Edited by wingover (01/25/17 03:59 PM)
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