[Hallb-engineering] [New Logentry] Follow-up Re: Follow-up Re: Controlled Ramp on VCL Flow

[kashy at jlab.org]

Logentry Text:
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After discussions with others and reviewing the datalogger, I think I found the root cause of the event that tripped some magnest in each Hall on Sunday night January 22,2018.
In summary there were two pressure spikes on the warm return to the purifiers. The first one tripped of most of the magnets that were effected, and the second tripped off two more.
My conclusion is the pressure spikes occured upon opening the warm return valve from the target in Hall C. This valve was opened with with the circuit pressure at about 9.5 on the first opening and 13 on the second. It should be possible to open that valve with the circuit at ~2.4 atmospheres and it may be possible to open it slowly. If after the suggested procedure below is tested and refined it is also possible that the target group and an additional control valve specifically sized to allow a slower depressurization of the target loops (for both Halls A and C), but I don't think that will be needed.

Attached are plots of All SC magnets supported by the ESR and a plot of the supply and return valves to the Hall C target with the target return pressure.

The system piping involved is fairly simple. One supply valve CEV6731C, one return valve CEV6741C, and one warm return valve which is a remotely controlled ball valve used for cooldown and warm up.

Things of note.

1) The supply and return valve started to close at the same time (22:39:30)
2) by 22:45 the pressure in the loop started to rise
3) at 22:53:34 the warm return valve was opened The pressure dropped over the next 30 seconds and caused the first pressure spike
4) at 22:54:07 the warm return valve was closed and the pressure started to rise
5) AT 22:56:01 the return valve was fully seated at -6.41%
6) at 23:03:09 the warm return vavle was opened causing the second pressure spike

I suggest if possible we should change procedure for target warm up to the following.

1) close and fully seat the cold supply valve CEV6731 as quickly as possible w/o upsetting the cold box especially the turbines
2) make sure the electric power in the target is off or will automatically do so.
3) close the cold return valve CEV6741 until the pressure in the loop starts to rise  
4) open the warm return valve slowly (quickly to 20 or 25% as it is a ball valve then in 2-3% steps until the return pressure CPI9541 starts to drop)
5) once the return pressure CPI9541 is falling close and fully seat the cold return valve
6) monitor the return pressure CPI9541 and when below ~1.4 atmosphere fully open the warm return valve

NOTE: 1 and 2 above may be switched


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This is a plain text email for clients that cannot display HTML.  The full logentry can be found online at https://logbooks.jlab.org/entry/3519598
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