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March 1998

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Subject:
From:
Bob Mesick <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 4 Mar 1998 08:46:19 -0600
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>Hi everyone,

>I recently implemented closed loop water recycling in an OA flux
>environment.  Resistence of treated water going back to the cleaner have
>been about 18 meg ohm resistence.   To give you some idea of usage, the
>process has been running for 2 months using about 600 gallons of make up
>water(city water).  However, in the past three days it has gone from 18
>meg ohm to about 10 without any abnormal usage.  I have two questions?
>
>1.  Is this normal?  Does the ion exchange unit go out that quickly or is
>it more gradual?
>
>2.  What is considered to be acceptable resistence level in the DI water
>for PCB Assembly cleaning?
>
>
>Thanks in Advance
>Thomas Han
>Ardent Systems, Inc.

Thomas,

You didn't state the size of your columns.  A mixed bed column will remove
about 12-14,000 grains of hardness per cubic foot of resin.  Multiply by 17
for ppm.  Most of what you have removed is probably from the makeup water.
Use RO water for a longer lasting columns.

10k ohms is not bad, but you are on your way to breakthrough.  As the column
fills, the leakage increases and the resistance will now steadily decrease.
Breakthrough is pretty quick once started.

Good Luck,

Bob Mesick
Remco Engineering
Water and Wastewater Treatment Systems
www.remco.com

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