<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta content="text/html;charset=UTF-8" http-equiv="Content-Type">
</head>
<body bgcolor="#ffffff" text="#000000">
Stephen:<br>
<br>
Good point ... in the past we've often used translucent Polyflo tubing
to hook up tools because it's cheap and almost universally available.
I agree that that creates an additional likelihood of creating algae.
Over the long haul, it's also almost guaranteed to get brittle and
break at some point as well. I think that we now use Parker PushLok
hose by default with different colors for supply and return ... but
there are lots of opaque and better quality hose choices than
translucent Polyflo.<br>
<br>
Additionally, even though it adds a bit of clear material, we've
learned the hard way that having a readily visible variable-area flow
meter provides and easy way to monitor gradual flow degradation. The
initial cost of these flow meters ... and they aren't that expensive
... pays for itself the first time you catch a reduced flow condition
in the early phases rather than waiting for a serious cooling flow
problem.<br>
<br>
Thanks,<br>
<br>
John<br>
<br>
<br>
Stephen CS Howe wrote:
<blockquote cite="mid:1318761379.2178.6.camel@samsung.tower" type="cite">
<pre wrap="">Dear John,
In my experience, the color of the tubes can make quite a difference to
the presence of alghe growths in the lines and filters.
Rather than use an anti-alghe treatment, if you use black or other dark
colored non-transparent tubes, it eliminates a lot of problems.
Of course, that won't help you with corrosion though.
Yours sincerely,
Stephen Howe
Company Owner
SDI Fabsurplus Group
+1 830 388 1071 (Mobile)
+39 335 710 7756 (Italy Mobile)
Skype: Stephencshowe
<a class="moz-txt-link-abbreviated" href="http://WWW.FABSURPLUS.COM">WWW.FABSURPLUS.COM</a>
Contact us now to buy and sell used equipment
and enjoy the benefits of cost-saving.
On Sat, 2011-10-15 at 08:57 -0700, John Shott wrote:
</pre>
<blockquote type="cite">
<pre wrap="">Keith:
While I'm confident that others will contribute some important
insights and recommendations to this discussion, let me take an
initial stab at discussing some of the issues and approaches that we
have tried. Note: I don't consider myself an expert in this area, but
have certainly had to deal with a lot of problems in these areas over
the years .... both in tools with local chillers and heat exchangers
and in tools connected to the building-wide process cooling water
system.
We've likely had more problems over the years with the building-wide
system and have tended to go to local chillers and/or heat exchangers
when we either encounter a corrosion problem or have a resistivity
requirement that cannot be met by the building-wide system. That
said, however, we also have periodically seen problems on our tools
with local chillers and/or heat exchangers.
Note: Just for reference, our building wide system is treated with
Nalco TRAC107 at a 2000 ppm concentration, a pH of 7.5 to 8.0 but it
ends up with a pretty low resistivity of about only 2000 ohm-cm (500
microSiemens/cm) by a closed-loop control system. We recently had a
problem due to a failed pH probe that resulted in water with a pH of
6-6.5 .... which begins to be bad news for aluminum and mild steel.
So, even a "professionally managed", closed-loop control system can
have problems and is an ongoing struggle.
Back to your local chiller ....
1. I think that it's always good to understand the metals in the
system .... including parts of the chiller as well as the materials in
your machine through which the water flows .... to understand how much
of a galvanic reaction problem you are likely to have. While we can't
always control these things, systems that have mixtures of aluminum,
yellow metals, and mild steel tend to be more problematic. A lot of
tool manufacturers seem to include quite a range of metals in contact
with the water.
2. Can you measure the pH of the water in your recirculating tank? If
it has gradually drifted away from 7-ish .... particularly if it gets
below 6.5 or so ... that may help to explain more recent problems. If
pH is either or low or high I'd try to fully exchange the distilled
water.
3. Do you have a resistivity requirement .... for example, if this
chiller is cooling RF supplies, then you need pretty high resistivity
water.
What are some other options?
1. Analyzing the chemical content of the stuff that you are capturing
in your filters is often useful to try to determine what is the
primary corrosion material .... or whether you may be seeing organic
material due to algae growth. I believe that the little systems with
open tanks are more prone to algae problems than truly closed loop
systems because of ongoing oxygen entrapment in the water.
2. Adding a little deionizing cartrigde, resistivity monitor, and
solenoid so that water can periodically be passed through the
deionizing cartridge. I believe that a lot of people will tell you
that something in the range of 0.5 - 1.0 Mohm-cm is about optimum.
High enough resistivity to reduce galvanic corrosion, but not so high
that the DI water corrodes everything in sight. Note: if you go this
route, you generally have a second solenoid controlled loop with the
deionizing cartridge in it in parallel with the main flow loop. That
is because you can't typically get 2-3 GPM through a deionizing
cartridge so you have a bypass flow channel that routes a little bit
of the flow through the deionizer when you need to increase the
resistivity. Plus, you are only shooting for 0.5 - 1.0 MOhm-cm and
don't want to be routing too much of the flow through a deionizing
cartridge. I haven't priced this in a while, but I think that you can
get a cartridge housing, a resistivity controller, and a resistivity
probe for on the order of $1k.
3. There are additives that claim to be able to be added to these
recirculators to inhibit corrosion with minimum monitoring or precise
control. For example, there is some stuff called Optishield (and
Optishield II and Optishield Plus ....) that you mix in at about a 10%
concentration with your distilled water. That is supposed to be good
for a year and then you empty the lines and refill with a fresh mix.
I have no personal experience with this stuff .... but maybe someone
else has and cares to comment.
4. We have used 50/50 mixes of DI water an ethylene glycol in a number
of tools .... particularly if they are going to be cooling to
temperatures near freezing. This mix, by itself, doesn't really
include much in the way of corrosion protection .... and, as I
understand it, if it is run to too long, can break down into a variety
of acids that will once again create problems.
Note: when we've had systems that have gotten significant build up, we
have used a variety of radiator flush type products ... with a fair
amount of trepidation .... to try to clear some of the "stuff" out of
a system. I'm not particularly proud to admit this ... but desperate
times call for desperate measures and a machine with a plugged (or
nearly so) cooling channel is a desperate situation if you can't
easily disassemble and/or replace cooling channels.
I fear that my conclusion is that we've tried a lot of things over the
years and still don't have a particularly good approach that has
resolved these issues on a permanent basis. Maybe some or our more
enlightened colleagues will provide a more comprehensive approach.
Good luck,
John
On 10/14/2011 6:31 PM, Keith Bradshaw wrote:
</pre>
<blockquote type="cite">
<pre wrap="">We have used distilled water in our chillers recirculating tanks.
Recently we have suddenly seen the inline filters clogged with
corrosion. We have seen more problems in the last 5 months than we
had in the previous 6 years.
Any advice on this?
Should we be using an additive?
cordially,
Keith Bradshaw
Garland, Texas
</pre>
</blockquote>
<pre wrap="">_______________________________________________
labnetwork mailing list
<a class="moz-txt-link-abbreviated" href="mailto:labnetwork@mtl.mit.edu">labnetwork@mtl.mit.edu</a>
<a class="moz-txt-link-freetext" href="https://www-mtl.mit.edu/mailman/listinfo.cgi/labnetwork">https://www-mtl.mit.edu/mailman/listinfo.cgi/labnetwork</a>
</pre>
</blockquote>
<pre wrap=""><!---->
</pre>
</blockquote>
<br>
</body>
</html>