Liquid helium transfer lines are used to
transfer liquid helium from a storage dewar to the magnet
system dewar.
These lines are usually constructed of all-welded stainless
steel. To aid in handling the line, the center section is
vacuum-jacketed flexible piping. This piping is connected on
either end to smaller diameter non-flexible vacuum-jacketed
tubing. These smaller diameter tubes are inserted into the
storage dewar and the magnet dewar.
Although LHe transfer lines are rugged and can give years of
service, they must be handled correctly in order to maximize
their lifetime.
It is very important that the non-flexible tubes are
inserted into the storage and magnet dewars in a straight up
and down motion. Bending the non-flexible tubing while it is
supercooled will apply too much stress to the welds and will
eventually cause failure.
Transferring liquid helium is a minimum two-person
operation. One person needs to guide the tube into the
storage dewar and the other person needs to guide the tube
into the magnet dewar. Each person should be positioned so
they may grasp the large curved tubing between the flexible
and small outside diameter tubing. Additional personnel may
be positioned at the tube ends to help guide the tube into
the dewars.
Stable platforms should be provided to stand on if the
storage or magnet dewar is too tall for personnel to refill
while standing on the floor.
Do not allow the weight of the transfer line to be supported
by the small outside diameter tubing!
Using proper equipment to protect the operators from
frostbite, have the personnel on the storage dewar leg
carefully guide the tube into the storage dewar until it is
slightly submerged in liquid helium.
Allow the transfer tube to cool until a plume is noticed on
the magnet dewar side leg of the transfer tube. The
personnel operating the magnet dewar leg should then
carefully guide the tube into place. It is very important
that all personnel handle the tube assembly by the large
curved tubing and the flexible tubing - not the small
outside diameter tubing!
After refilling the magnet dewar, carefully remove the
transfer tube by pulling straight up using the large curved
tubing. Use extreme care not to bend the small outside
diameter tubing of the assembly.
SEALING PROCEDURE TO BE FOLLOWED AT THE COMPLETION
OF EACH HELIUM TRANSFER:
- 1. Minimize the time the
system is open to the atmosphere during liquid helium
transfer
- This is the most likely time for air
and water to be drawn into the system.
- 2. Immediately following
helium transfer, seal all valves and fittings
- Carefully check all hoses, pop-off
valves, etc. for leaks by wiping soapy water over all
connections and watching for bubbles to appear.
- 3. Monitor off-gas from the
system using an appropriate gas flow meter
- Helium flow should begin within 24
hours after sealing the system. If gas flow through the flow
meter is not detected within 24 hours, recheck all seals
carefully and determine whether a High Pressure Atmospheric
System has moved through your area during the past 24 hours.
If one has, monitor the flow for another 24 hours.
- 4. Periodically check the
flow meter on the system to see that helium gas is flowing
out of the system
- If gas flow is not detected for more
than 24 hours, recheck all fittings as described above. If
no off gas is generated within another 24 hours,
CONTACT THE FACTORY IMMEDIATELY!
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