At Sparky,
I would strongly vote against wrapping a transfer line with a heating mantle (I guess
you mean to heat it up during vacuum pumping to bake out trapped gases?): As the transfer
lines are dual-layer stainless flex tubes with **plastic** spacers every 10-20 cm or so
to prevent the inner tube from touching the outer tube, these spacers won’t like
being baked at typical temperatures used in this process (up to 300-400 deg C)!
I don’t guess you mean to wrap the tube in “domestic heating tubing”
made of neoprene or similar - this won’t help at all avoiding bad helium boiloff because
of bad vacuum inside a trsnsfer line…
Btw. a first sign that the transfer lines are is soon due to be pumped is if the line is
nice and warm during refill but gets really cold right after the filling is done: trapped gases
will freeze onto the inner tube but get released once no helium flows through it anymore
after the refill (you may be able to spot the plastic spacers in this case -less moisture
condensation around them). A transfer line with truly good vacuum stays (mostly) warm on
the outside even after a refill.
Be sure to clean & regrease the O-ring before pumping (may have gunk inbetween screw
and surrounding).
Happy refilling,
Bert
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