You are viewing an old version of this page. View the current version.

Compare with Current View Page History

« Previous Version 16 Next »

On we started the Liquefier A after cleaning up the Dewar A level sensors using the procedure (docdb). According to the procedure, the bottom tube did not vent gHe on when the cold head temperatures are slightly above 240 K. So, we had to wait until all the cold heads are above 272K.
Image


Since then (03/06/2023), Dewar A wasn't producing liquid until the 03/19/2023 afternoon. Below is the log of things that we did.


Around 11:26am on 03/12/2023
1. Set the "Mode End: Coldhead Temperature" to 3 K
    Screen_Shot_2023-03-12_at_11.26.33_AM.png
2. Had to switch the LQ-A to the Manual mode for a minute and the switched back to Liquefy mode to enable the change made in the previous step.
3. See the cold-head temperatures since 03/06/2023.
    Screen_Shot_2023-03-12_at_9.21.51_PM.png
4. Flow change after making the change on Mode End: Coldhead Temperature" to 3 K.
    Screen_Shot_2023-03-12_at_9.22.28_PM.png



On 03/14/2023

LQ-A is still the same, LI501 shows 0.2 L. Adam suggested changing the outlet flow to 24 slm and I just changed it on the LQ-A Settings screen.
Screen_Shot_2023-03-14_at_9.48.39_AM.pngScreen_Shot_2023-03-14_at_9.48.57_AM.png

The issue was that, the FCAI hasn't go up beyond ~8slm although FCAQ is set to 24slm.
Then, on 03/14/2023 around 4:20pm CST, we closed the NV501A needle valve as Adam suggested, to improve the Liquefaction on LQ-A. It was between 1/4 and 1/2 a turn opened position before it was completely closed.
     NV501_03-14-2023_After_02.jpg



On 03/15/2023 around 2:20 pm
We opened the NV501A needle valve by two full turns from the current setting(fully closed position) as Joey (QT) recommended.

On 03/16/2023
1.  In addition to the 2 turns (open) on 03/15/2023, NV501A was opened with one more full turn.
2. We adjusted the PRV501A, in order to obtain a smooth inlet flow.
       (Initial Position)                                                                                                                                                                                                                                 (Final Position)
    IMG_2790_Before_At_16_18.jpgIMG_2791_Position2_At_16_21.jpgIMG_2792_Position3_At_16_30.jpgIMG_2794_Position4_At_16_31.jpgIMG_2799_Position5_At_17_10.jpgIMG_2806_After_At_17_36.jpg

* We noticed that it takes about ~10min response time after changing PRV501A.


On 03/18/2023
In addition to the 3 turns (open) since 03/16/2023, NV501A was opened with one more full turn.
PRV501A was opened slightly a bit (~1/8th of a turn).


On 03/19/2023
After 13 days of starting the Cooldown of the Liquefier A, today the level sensor indicated that the Dewar A has started accumulating liquid. Notice that the outlet flow actual value is around ~13slm although FCAQ is still set to 24slm.





A screen video of Liquefier A

https://myuva-my.sharepoint.com/:v:/r/personal/dmk9m_virginia_edu/Documents/Attachments/DewarCooldown.mp4?csf=1&web=1&e=863qws

Liquefier_A.mov


Dewar Cooldown Mode:

Historically we have had more trouble with cooling Dewar A down than Dewar B.  Dewar A has taken more than 3 days in the past and this most recent time (March '23) its taken about two weeks.
LQ_A_Cooldown_09_12_2022.png
This is likely just because the settings were not optimized for cooling and we had better pay more attention to the system setting for switching between production and cooling modes.  If the pressure in the dewar is greater than that on the cold heads the dewar will never cool and the system enters a perpetual state where the cold heads are cold but the dewar is warm.

It seems that the green-handled regulator on the QT manifold should not be open too much.  This will make the MFC letting in the helium to the cold heads fluctuated a lot which is not optimal for cooling.  During cooldown mode you want a large flow running in and out of the dewar with the goal of around 60 slm going in and 24 slm going out.  In order for this to work the pressure in the cold heads much stay slightly above the dewar pressure so flow continuously runs to the dewar to cool things down.  The black-handled needle valve should be open a lot (maybe all the way) to keep the flow through this area as high as possible.  This will lead to lots of frost and ice build up on the dewar neck.  This should not be a problem but should be checked and defrosted regularly.  When everything is set appropriately the accumulation of liquid should happen in about 24 hours.





  • No labels