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 Post subject: Filtering and flow rates
PostPosted: September 10th, 2017, 13:58 
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Joined: April 1st, 2016, 21:26
Posts: 57
Location: United States
Im considering putting together something of a clean glove box for head replacements.

Im not super worried about the physical build. I have a laser cutter and CNC for any cuts/fabrication.

I know others have done this with tupperware containers and plastic wrap and whatnot. From what I've seen, they do not introduce filtering and laminar flow. Which as we know is essential to a proper clean environment.

Im quite sure i can build something from the ground up.

I have not been able to find any numbers on ideal flow rate and filter ratings for such an environment. Does it vary from device to device? Is there a standard? Does it not matter as long as it's consistent?


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 Post subject: Re: Filtering and flow rates
PostPosted: September 10th, 2017, 14:49 
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Joined: December 8th, 2010, 11:37
Posts: 512
Location: Ottawa, Canada
Have a look at my clean chamber project for some ideas, if you haven't already. IIRC, the desired flow rate is 0.5m/second, based on the helpful information at this site (bottom half has the calculations). Do share pictures of what you end up building.

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 Post subject: Re: Filtering and flow rates
PostPosted: September 10th, 2017, 15:05 
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Location: United States
LarrySabo wrote:
Have a look at my clean chamber project for some ideas, if you haven't already. IIRC, the desired flow rate is 0.5m/second, based on the helpful information at this site (bottom half has the calculations). Do share pictures of what you end up building.


Excellent, yes i saw that, i was actually planning on reaching out to you.

Do you have a video of yours in action? It may answer many of the questions i have about how it works.

Just in general, I'm guessing that is not a pressurized system? My initial plan was to do make an airtight unit with inlet filtering and a variable flow rate (suction) on the outlet. That way it could be tightly controlled over the work area. Blast it for a 30 seconds to clear the chamber, then adjust to an ideal flow rate to begin working.

I understand the purpose of the flow is to isolate the workpiece from contamination, but wouldn't it be beneficial to have the work area be devoid of contamination to start with?

Am i overthinking this? Am i underthinking this (ha)?


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 Post subject: Re: Filtering and flow rates
PostPosted: September 10th, 2017, 19:56 
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Joined: December 8th, 2010, 11:37
Posts: 512
Location: Ottawa, Canada
I'll upload the video I had posted a link to earlier, but seems to no longer be available. It shows the airflow test I did and gives an idea of the noise level. I thought about doing what you suggest, with a vertical airflow cabinet. It was going to have feedback air columns on the side and a baffle that controlled the proportion of air that was fresh vs re-cycled from inside the cabinet. The feedback sir stream was returned to the "unfiltered" side of the filter, of course. The intent was to reduce the rate at which the filter got clogged with particles. I abandoned the idea because of the complexity.

Most vertical flow cabinets are left to run for a minute or two to remove any unfiltered air before opening up the patient hard drive. With horizontal airflow, no need to do that as all the air is filtered within seconds of turning it on. I usually leave the "sneeze-guard" down to increase the speed with which any interior air is cleared and to increase the air velocity. There is more than enough airflow velocity even with the lid fully raised,so it's really not necessary, I think.

Larry

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 Post subject: Re: Filtering and flow rates
PostPosted: September 11th, 2017, 13:19 
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Joined: December 8th, 2010, 11:37
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Location: Ottawa, Canada
Here is the video I mentioned: https://www.dropbox.com/s/if28g6b8r4yjo ... 4.mp4?dl=0

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 Post subject: Re: Filtering and flow rates
PostPosted: September 11th, 2017, 13:55 
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Joined: April 1st, 2016, 21:26
Posts: 57
Location: United States
No rush, but do you happen to have a video of performing a repair in this machine?

Ive not yet begun anything beyond planning, but I've found a cheap($15) particle counter/air quality meter that is good down to 1 micron. If i decide to go whole hog on this, i believe i can measure airflow with something like MAF sensor, use that to adjust airflow digital. I have also found an all in one sensor for temp, pressure and humidity. I think it could be interesting to have a real time view of the air quality inside the chamber.

Is there a tangible benefit between vertical and horizontal flow? my intuition says to go with horizontal, but vertical must exist for a reason


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 Post subject: Re: Filtering and flow rates
PostPosted: September 11th, 2017, 16:58 
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Joined: December 8th, 2010, 11:37
Posts: 512
Location: Ottawa, Canada
senordingdong wrote:
No rush, but do you happen to have a video of performing a repair in this machine?

Not really, unless you call this one I made on a junk drive demoing how I did a platter swap on a 7200.11 without much joy.

Quote:
Ive not yet begun anything beyond planning, but I've found a cheap($15) particle counter/air quality meter that is good down to 1 micron.

:shock: Really? Do share a link, please. The Dylos DC1100 Pro at $260 USD is the cheapest particle counter I have found.

Quote:
If i decide to go whole hog on this, i believe i can measure airflow with something like MAF sensor, use that to adjust airflow digital. I have also found an all in one sensor for temp, pressure and humidity. I think it could be interesting to have a real time view of the air quality inside the chamber.

I think you are probably over-thinking/over-engineering this. :wink:

Quote:
Is there a tangible benefit between vertical and horizontal flow? my intuition says to go with horizontal, but vertical must exist for a reason

I haven't been able to find any research on the question and suspect it's just personal preference and cost. Vertical flow units often use filters smaller than the cross-sectional area of the chamber, whereas horizontal units seem to usually have filters that span the entire width. I may be wrong about that, as it is possible to draw air into the plenum through a smaller filter and let it expand/diffuse then exit through a larger screen at the back of the working area, so that weakens that argument. LOL. My own reasoning for preferring horizontal is that vertical units tend to let particles from the drive lid, tools, hands, etc. fall down onto the working area, whereas horizontal units tend to blow it horizontally, away from it. Vertical units don't have a wind-in-the-face effect, which horizontal units do, unless they have a sneeze guard/sliding-window-blind panel that deflects it.

Anyway, good to see someone else (other than all the 'shroom enthusiasts) interested in building their own unit.

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 Post subject: Re: Filtering and flow rates
PostPosted: September 11th, 2017, 17:27 
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Joined: April 1st, 2016, 21:26
Posts: 57
Location: United States
https://www.amazon.com/Air-Quality-Sens ... B00P03TFT4

http://www.robotshop.com/en/grove-dust- ... 0PEALw_wcB

Its IR rather than Laser, but all my research I've done into it suggest that it works quite well.


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 Post subject: Re: Filtering and flow rates
PostPosted: September 11th, 2017, 19:31 
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Joined: December 8th, 2010, 11:37
Posts: 512
Location: Ottawa, Canada
Thanks.

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 Post subject: Re: Filtering and flow rates
PostPosted: September 12th, 2017, 17:39 
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Joined: July 12th, 2010, 4:38
Posts: 994
Location: Portugal
Yeah, but that's only the sensor. You also need to buy the Arduino and program it, right?
This one is already built, just don't know what's the size of the particles it can detect.
http://www.ebay.co.uk/itm/SAMON1-PM2-5- ... Sw5h5ZdavG

This one can even go to 0.3...
http://www.ebay.co.uk/itm/Household-PM2 ... SwWmhZiZYk

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 Post subject: Re: Filtering and flow rates
PostPosted: September 12th, 2017, 18:09 
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Joined: April 1st, 2016, 21:26
Posts: 57
Location: United States
Nice, that seems like a better solution.

Yeah i have more than a few arduinos hanging around, so not a big deal, but yes an additional expense.


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 Post subject: Re: Filtering and flow rates
PostPosted: September 12th, 2017, 21:32 
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Joined: December 8th, 2010, 11:37
Posts: 512
Location: Ottawa, Canada
pclab wrote:

Wow, terrific find! I've just ordered one. Now I just need to find someone who has a calibrated particle counter so I can see how accurate this one is.

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 Post subject: Re: Filtering and flow rates
PostPosted: September 12th, 2017, 21:36 
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Joined: April 1st, 2016, 21:26
Posts: 57
Location: United States
please do report on your results. that .3 resolution is amazing for the price if its even kind of accurate. Assuming it can be trusted, you could get a really nice picture of what class your clean environment equates to.

Ive definitely added this to the parts list


In regard to your home built unit, do you find human/user contamination to be an issue, or am i getting too Walter White about this?


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