Comment AG4108 SNF 2009-06-26 17:48:41: Chilled water differential pressure ....

shott at shott at
Fri Jun 26 17:48:41 PDT 2009

For quite some time (like since last fall), the chilled water supply/return
pressure differential has bee quite limited.  At that time, the supply
pressure was only about 62 PSI and the return pressure was about
40 PSI.  Not good for a tool that specifies a minimum of 30 PSI.
Several weeks ago, while pondering this, I looked at nearby tools
that used chilled water.  From a piping perspective, the closest tools
are the Tylan and Thermco furnaces.  Most of them did not have flow
meters.  The one that did, however, was the LPCVD bank (tylanpoly,
tylannitride, tylanbpsg, and tylanfga).  It was flowing 7 GPM.  According
to the Tylan specs, even if all 4 tubes were running at 1200 C, we would
only need to flow 2 GPM to keep the exhaust air temperature at 100 F!!!
Note: and even if we didn't have enough cooling, that shouldn't directly affect the tools or the process .... it is only the heat exchanger that cools the air before it goes back into the room.
Me thinks we are using way too much PCW at the Tylans and Thermcos.
I have since asked Ted and Ray to acquire and install flowmeters at each furnace and then to throttle back the flow to provide 2 GPM.  I believe that has now happened on all banks but the old Pacific Western.
The results: as of yesterday at either AG, the PCW supply side pressure
was 72 PSI and the PCW return pressure was 36 PSI.  Differential pressure has increased from 22 PSI to 36 and flow through each tool is between 1.8 GPM and 2.0 GPM.  While those flows may still be a bit marginal .... possibly due to "sand" buildup.  The differential pressure readings
are far better and we are now meeting specifications is that regard.

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