[DIYbio] Re: low cost positive pressure laminar flow HEPA filtered box

The link takes you to a particle detector. It would have to be built and, more importantly, maintained/calibrated to be a measurement tool that could direct action. While a (maintained/calibrated) particle detector would help find particle leaks inside your clean chamber, it wouldn't tell you something more relevant to your goal: reproducible inoculation of growth media. If that's your goal, that's what you should measure. That looks to be the point of this comment:
https://groups.google.com/d/msg/diybio/9-A-EHhJxN4/PYVnNiUrMK8J
There is probably an official name/test protocol for it but let's call it the Petri test for this commentary. I will happily change what I call it if someone has a link to the protocol for this type of test.

Cheap "is-air-flowing" indicator (the scrap of fabric-> wind sock) and a cheap "is-the-filter-too-spent" indicator (manometer) are indirect measurement of your target result (reproducible inoculation) but they are cheap and their measurement directs action (turn on air flow motor and time to change filter). The problem with the Petri test is, on failure, you have to do more and different tests to direct action. Over time, you would probably develop Petri test data patterns for your clean hood that provide enough information to direct action.

I wonder if you could assess sufficient keeping-stuff-out by a different take on helium leak detection? The measurement of relative humidity is fairly well characterized. An Arduino version can be obtained very inexpensively. With a modicum of care, the RH meter can be maintained cheaply. Set the RH meter inside the clean box, close it as in regular use, spritz water or run a water-soaked cloth along ostensibly sealed outside edges while watching the meter. If there is an outside to inside path for the water, the RH will rise. This gives you information to direct action, too.

Cindy

On Friday, July 18, 2014 2:57:02 PM UTC-7, John Griessen wrote:

On 07/18/2014 04:30 PM, Nathan McCorkle wrote:> I think common lingo just calls what you're describing a clean air
 > hood, nerdier folks call them positive-pressure hoods.
 >
 > I could be wrong, but that's been my understanding for the past 5 years or so.

A hood suggests a vent to a duct in the building, so I did not want to talk that way.
Leaving out the words laminar flow would be such low braggability...

So how's the new subject line sound?

On 07/17/2014 11:00 AM, CindyB wrote:
 > If you flood your intake side with particles to see how many get through you will have used up the fouling capacity of your filter
 > with your test.

There must be some way such tests are done without using up the filter, because some companies brag about it.
By flood, maybe I used the wrong, non-quantitative word.  They probably do not use a shovel to add
test sphere particles, but a puffer, duster, air siphon mixer of some kind similar to a siphon spray gun for liquids..

In industrial manufacturing HEPA flow hoods, tests consist of:1)  testing flow rate of air on the clean side;
 > target: not too fast, not too slow 2) industry standard particle detector test on the clean side; target: no particles in
 > detection range 3) pressure drop across the filter; target; not too high
 >
 > I didn't give quantitative targets because it depends on the industrial requirements. I could see a low budget way of assessing
 > flow rate with a small strip of cloth as in a wind sock and a home made water manometer (for pressure drop). Not sure how to get
 > the particle detection.

What do you think of this:
http://www.sca-shinyei.com/pdf/PPD42NS.pdf