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Tuesday, October 18, 2011

Vacuum Systems

     Dear Dr. Lieberman – I have purchased many of your books, in which you have kindly invited questions. My question pertains to our new vacuum tower operation. Every morning about 10:00 AM, our vacuum ejectors start to make a regular sound. The operators say the ejectors start to breathe. At the same time our flash zone pressure increases from 10 to 12 mm of mercury to about 20. Any suggestions you may offer would be sincerely appreciated.
--Amed

     Amed – Your jets are surging. Most likely, because of higher discharge pressure. The cause of the higher discharge pressure is probably an increase in the plant’s cooling water temperature as the sun comes up. When I say your jets are surging, I mean that they are losing their sonic boost as described in my book, Process Equipment Malfunctions.
     To start with, try back-flushing the condenser water side on the discharge of the surging jet. Unfortunately, there are dozens of different things that can cause jets to surge. But anything you can do to improve water flow through the downstream condenser is sure to help to some degree.
--Mr. (not doctor) Norman Lieberman

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