Reports until 16:24, Wednesday 31 May 2017
LHO VE
chandra.romel@LIGO.ORG - posted 16:24, Wednesday 31 May 2017 - last comment - 19:57, Wednesday 31 May 2017(36576)
CP3 clog gone....maybe

We have reason to believe that CP3 is fixed and the ice blockage is gone. However, there was an auto overfill today at 11 am which may be skewing the reading, so we will let things settle overnight. Reservoir level reading is 100% on Beckhoff (software limit) and 120% on Magnehelic. Today we found the sensing line valves open to transducer, along with the valve that isolates them from each other, so we have been flowing much of the GN2 straight out the exhaust. Kyle checked these valves last night and thought the isolation valve was closed, but turns out it was just sticky and actually open.

We connected GN2 to CP4 sensing line, and will leave it connected for days vs. hours this time (readout on MEDM falsely shows 100% full). The flow is essentially zero right now, but set to 2 LPM in case it does open up. Isolation valve between two sensing lines is closed.

We are leaving CP3 LLCV in manual mode tonight.

 

Comments related to this report
kyle.ryan@LIGO.ORG - 19:57, Wednesday 31 May 2017 (36579)
1915 - 1930 hrs. local 

I had to convince myself (again) that we don't still have residual LN2 from today's overfill trapped between the current/former sensing line blockage and the, now closed, exhaust path.  Since the valve separating the exhaust sensing line from the bottom draw sensing line (a.k.a. the low pressure line vs. high pressure line) was open during today's overfill and the fact that the pump's exhaust line is at the highest elevation, it is conceivable that the sensing lines are filled with LN2 during an overfill.  If so, then following an overfill, if this valve gets closed, as happened today, LN2 could be trapped with no exhaust path as it converts to GN2. The resulting pressure would "test" the bi-braze joint and blockage.  There could be LN2 still in the portion of the sensing line within the vacuum vessel even though the external-to-vacuum portion of the line is "warm" and having no frost.  So, I (again) opened this valve to provide a path to atmosphere but observed no evidence that there was any pressure release or flow (I really do need to make some friends and to "get a life").  For CP4 the 1/4 polyflo tubing and acrylic rotometer effectively provide pressure relief as they would split long before the bi-braze joint.  For CP3, I left the magnahelic differential pressure gauge valved in and it should fail in such a way as to relieve any extreme pressure long before the bi-braze joint.  

0800 - Leaving site (again)