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Shop: Unfolding Nature Unfolding Nature: Being in the Implicate Order   PhytoExtractum Buy Bali Kratom Powder

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OfflineHide
I Have No Bung Hole
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Registered: 11/25/14
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Flow hood FPM a bit high and patchy
    #27116530 - 12/30/20 03:14 PM (3 years, 29 days ago)

Finished my first flow hood today. Have an anemometer handy.

Using a fan speed controller to achieve desired FPM. Getting 98.4 - 118 FPM in most spots, if I hold it closer then it goes up to 133-177.

But I don't think that would be a correct way of measuring, as you'd be working away from the hood and not right up against it.

At one point it was just the top right corner showing the highest reading of 177 but think I have sorted, going to double check tomorrow.. will I be ok in these sort of ranges?

Should I be measuring further away, in the space that I'll be working? Thanks


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OfflineCyonic
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Re: Flow hood FPM a bit high and patchy [Re: Hide]
    #27116611 - 12/30/20 03:53 PM (3 years, 29 days ago)

Those devices are not necessarily 100% accurate but should give you a good idea.

Double check using a candle or a brand newish bic lighter, or something producing fumes such as incense or cig/joint.

I think the candle or lighter are ideal testers because they will be put out if the flow is too strong.vif it bends to 90° without going out you're good.

What kind of fan are you using? Squirrel cage or inline?


Edited by Cyonic (12/30/20 03:54 PM)


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OfflineHide
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Re: Flow hood FPM a bit high and patchy [Re: Cyonic]
    #27116619 - 12/30/20 03:57 PM (3 years, 29 days ago)

Thanks man. Lighter test looked good, it's a centrifugal fan


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OfflineProfessor X
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Re: Flow hood FPM a bit high and patchy [Re: Hide]
    #27116648 - 12/30/20 04:14 PM (3 years, 29 days ago)

I always liked the incense testing method. Gives the most accurate appraisal in my opinion.


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Invisiblemicelio
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Re: Flow hood FPM a bit high and patchy [Re: Hide]
    #27116741 - 12/30/20 05:16 PM (3 years, 29 days ago)

Hide..

If It's obvious that you have different air velocity though out the face of your filter Is not a good sign.

that's an indication that you do not have a laminar flow.

Different air speed could cause turbulence that could draw contaminated air into your work area.

I suggest that you work as close as possible to your filter as you can.

What could be the cause of uneven velocity Is maybe too small of a plenum area or just a bad filter blower match up.
You want approximately 1 inch of wg. in the plenum.

Use a bic lighter two inches in front of your filter. The flame should be at about 45 degrees with no turbulence, or very little turbulence.

You can control the airspeed by restricting the air going into the blower intake with duck tape and sheet metal or anything of that nature.

The more you restrict the flow the less amperage the blower will use.

Motor controllers that uses resisters and uses heat sinks to dissipate the heat off the resister don't save you that much on your power bill.


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OfflineRoscoeReturnsS
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Re: Flow hood FPM a bit high and patchy [Re: micelio]
    #27116948 - 12/30/20 07:27 PM (3 years, 29 days ago)

Take velocity readings 6” from the filter face, on a 6” x 6” grid. Average of all readings should be 100fpm +/- 20%, and all point readings should be within 15% of the average. That’s how we test LF hoods in the field


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