Comment mrc SNF 2012-07-23 18:30:41: Intermittant Foreline burst during roughing

[jimkruger at snf.stanford.edu]

About half the time, the foreline pressure rises suddenly, 20 or 30 sec into the roughing time.  Stop roughing (center switch position) ~ 10 sec, pump the foreline back below ~ 25 mTorr, then go back to roughing.
High foreline pressure causes the diffusion pump to stop pumping and can diffuse oil back into the pump stack.