From shott at snf.stanford.edu Fri Jun 26 17:48:18 2009 From: shott at snf.stanford.edu (shott at snf.stanford.edu) Date: Fri, 26 Jun 2009 17:48:18 -0700 Subject: Comment AG4100 SNF 2009-06-26 17:48:18: Chilled water pressure differential .... Message-ID: 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. Thanks, John