Subject: Re: Checking HEPA filters?

From: [email-masked] (Mark Spear)
Date: 3 Nov 96 01:35:00 -0800

Have you tried "scanning" the filter face with an open petri dish?  
This won't reveal small problems but will give you a general idea.

Another crude method is to buy, borrow, rent or make a hot wire 
anemometer (less than $250) and scan the filter face.  Look for spots 
where the air is moving faster than the surrounding.  These could be 
holes or split seams.  Also see if there is sufficent air velocity.  
If you can't get 70-80 fpm the filter may already be plugged.

Concerning holes and splits.  In many cases these are repairable with calk.  

    ---- Mark

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From: [email-masked] (Steve Carpenter - Cascade Research Assoc.)
Date: 3 Nov 1996 17:18:14 GMT

A dry-ice fogger to check for airflow distribution within any HEPA filter 
system:

1. Purchase a 2' length of 4" diameter plastic pipe.  I use ABS sewer
   pipe.  Close off one end, being sure to use glue to make it watertight,
   and thread the other end so that you can place a screw-on cap on it. 

2. Fit the side of the pipe with a plastic or metal tapered pipe fitting
   over which you can place a 1/2-5/8" diam, 2-3' length of flexible, clear 
   tubing.

3. When you are ready to test, open the cap and put about a half quart to
   a quart of hot water.  Throw in a good chunk of dry ice.  Screw on the
   cap.

4. Presto! - out comes fog through the clear tubing in the side of the 
   pipe.
 
  You can the use the fog in the chamber to see if the air is blowing 
properly.  If you can access the plenum area above the filter, you may be 
able to see leaks through large holes, depending on conditions.

I have use this apparatus to successfully test many HEPA units in cleanrooms.

-Steve Carpenter, Ph.D.
 Cascade Research Associates
  & Abbey Lane Laboratory
 [email-masked]

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From: Joe Harrington <[email-masked]>
Date: 4 Nov 1996 01:30:29 GMT

posted/[email-masked] (Steve Carpenter - Cascade 
> Cascade Research Associates

Thanks for the informative responses regarding checking the filters.

I picked up the unit today in Mass.  It was a bit BIGGER than I 
anticipated, the filtered area was 72" by 32", and the entire cabinet
was custom made. I did some preliminary tests and it looks in very 
good shape and I'll try out the other suggestions. 

It was QUITE a challenge moving and we had to disassemble it 
to get it down the basement step.  But all in all, quite a deal for $450.

Thanks again to all respondents.

Joe