Activated carbon beds

There has been some discussion of how to tell when an activated
carbon bed in your gaseous pollution filter system is exhausted. I
remembered Bill Lull describing this in one of his talks, so I
called him to get the whole story.  He had advised us to mix a
handful of Purafil's (or anybody else's) potassium
permanganate-saturated pellets in with the carbon when you refill
the bed.  Examine them when you think the bed may be reaching
saturation; if they are still purple, you still have some time to
go.  When they turn grey, it's time to change the carbon.

However, that's just a rule of thumb, because the two agents do not
absorb identical sets of gases.  If you want to be exact, you take
out a sample of activated carbon and mail it to Purafil or wherever
for analysis.  (They are in Doraville, GA, at 800/222-6367.) Purafil
analyses it free.  If the bed is exhausted, they get to sell you
some more.

Another company named Extraction Systems is working on a field test
for analyzing air upstream and downstream from the bed, which would
be even more exact, because the purpose of installing these things
is to purify the air, not to pollute the filters.  They got the
contract for the new National Archives building, and they come
around four times a year to maintain the system.

I *think* I got all that straight.

Ellen McCrady, Editor
Abbey Publications
7105 Geneva Dr.
Austin, TX 78723
512/929-3992
Fax:  512/929-3995

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                  Conservation DistList Instance 11:62
                 Distributed: Tuesday, January 20, 1998
                       Message Id: cdl-11-62-002
                                  ***