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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.

Questions

a.) Is there a downside to having the needle valve open too much during the dewar cooldown?

b.) Are the seals at the top of the neck something we should try to keep warm or will this run into contamination issues?

c.) Do we understand why the overfilling (just up to 220L) leads to this contamination issue?  Can this be fixed with different tubing?
     With past experiences, the level sensor's large fluctuations happened if the Dewar was kept full ( > 210 L) for more than two or three days.