(Foggy memory) I think, the manual settings for CP5, CP6 and CP7 are currently lower than needed to maintain pump levels (more like 80%, 60% and 80% respectively?).
patrick.thomas@LIGO.ORG - 21:26, Tuesday 19 April 2016 (26670)
Kyle - yes on those values. I trended the data over 30 days. Manual values were set very low.
I am at the lab. I've been simulating a PID with manual control of valve opening while watching real time trends. I manually filled CP5 as soon as I got here. Took about 19 min. to get to 100%. Then I adjusted valve settings in control room and decided to manually fill CP6 because it was dropping to below 85% (after raising valve level to 65%). I turned bypass valve half turn (with bypass exhaust valve open). The bypass LLCV is stuck open! I cannot close it. So I currently have the LLCV set to 0% and the bypass exhaust valve open. Pressure reads 0.0 psi. I'm waiting and hoping the liquid level falls below 100%. I'm not sure how 1/2 turn equates to LLCV percentages.
chandra.romel@LIGO.ORG - 01:30, Wednesday 20 April 2016 (26672)
I went back out to CP6. When bypass exhaust valve is closed, pressure reads 0.7 psi. I left it half way open. Pressure reads 0.1 psi.
Level is still 100%+ with LLCV bypass valve stuck 1/2 turn open. I am guessing it is frozen open. The pipes there are really cold. Exhaust pipes are frosty.
kyle.ryan@LIGO.ORG - 01:41, Wednesday 20 April 2016 (26673)
Chandra - you're kind of weird chick - I like you. We can now deal with this in the morning! Keep in mind that we have past data to suggest that 60% full doesn't translate into off-gassing and that the pumps boil-off at ~2.5%/hour when LN2 flow is stopped altogether so we don't need to go full "Kyle" just yet. Still, it i comforting to know that someone else is "sick" with worry about getting caught off guard regarding the 80K pumps!
chandra.romel@LIGO.ORG - 02:05, Wednesday 20 April 2016 (26674)
I am breaking records for trips to CP6 in one night. Bad idea to partially close bypass exhaust valve. Lots of N2 vapor and liquid started pouring out both ends (pressure is ok). So I closed the main Dewar valve. Then I opened it just a half turn. Back to liquid and vapor pouring. So it's now fully closed. *Everything* is cold so I think the system will be safe until crew arrives in morning to try to thaw bypass LLCV.
-Oh, just read your data, Kyle. Great! 2.5%/hr loss when main valve is closed tells me I can go home to bed!
john.worden@LIGO.ORG - 09:21, Wednesday 20 April 2016 (26680)
09:00 local time. I drove out to MIDX to check on the frozen valve. It is now free as the transfer line has warmed up overnight.
I left the dewar shutoff in the closed position and will leave it there until the CP6 level falls below 100%.