Subject: Re: Problem sem4160 SNF 2012-10-01 18:56:53: S.C. leak?
From: jwc@snf.stanford.edu

this is a normal event over the past year due to trapped gas behind the slit valve or
possibly a micro leak in the isolation bellows.
seem this problem before on other S4100 series SEMS with prolonged age and operation
time...
to be disregarded for now