🚀 go-pugleaf

In article <459ab2$58e@nntp5.u.washington.edu> Shekhar Mande <shekhar@gouda.bmsc.washington.edu> writes:
>One of the possibilities could be (which we accidentally encountered during
>our runs)- is when the cryo-system was brought down by a user, all the liquid
>N2 was not drained from the smaller dewar of the MSC system.  Due to this
>the nozzle sucks in some water, which remains in the spiral tube.  If another
>user starts the cryo-system next day or a day later, the water inside the
>spiral freezes, causing rapid changes in the temperature of the cryo-flow, and 
>some ice also falls from the nozzle onto the xtal.  The remedy is ofcourse
>to dismantle the smaller dewar, and heat the spiral tube, which would evaporate
>residual water in the tube and then start the gas flow before inserting
>the spiral tube into the dewar again.
>
>Shekhar
>

Yes, we have experienced this in the past.  I am sure this is not the problem 
we are experiencing this time since the dewar had been emptied a day earlier 
and I had used heating tape on the coils while purging with N2.  We did not
have a blockage, but I wished to be sure that the system was very dry.  After 
reassembling, we once again had similar problems once the system had cooled 
down.  The problem seems to occur around the entry point for the auxillary 
flow.  If a soft mallet is taken and the transfer tube tapped gently at the T, 
you get a cascade of ice crystals.  If you fail to clear the tube regularly, 
the aux flow will eventually ice closed and at this point, you need to 
disassemble the system and allow the ice plug to evaporate.  I have sealed 
every joint I can identify trying to prevent this blockage, but it always 
reappears.

Kevin