Transferring Liquid Helium:

These are genral guidelines. The types of cryostats and transfer tubes vary, plus other conditions change, making each transfer unique.

If you have not been trained (at UF) you should not be transfering liquid helium. Training is the responsibility of the P.I. for the lab where the transferring will take place. Cryogenics personnel will assist in training when requested.

Safety equipment should be employed.

1. Connect the transport dewar recovery hose to a helium recovery system port in the lab near to where the transfer will take place. Verify that the ball valve for that hose is open.

2. Verify that the transport dewar pressure is at or very near recovery pressure (~3"H2O).

3. Measure the liquid level in the transport dewar manually and record it on the transport dewar chart. If the dewar is equipped with an electronic Helium Level Detector, use it instead. HLD instructions

4. Make note of the gas meter counter number.

5. Connect a source of pure helium gas (5 psig MAX.) to the hose barb fitting.

6. Confirm that you have the correct adaptor fittings for your transfer tube, and that all o-rings are present, in good shape and seated properly within the fitting..

7. Place the transfer tube into the top port on the transport dewar, keeping the ball valve there closed.

8. Crack open the valve to purge the transfer tube of air.

9. Insert the other end of the tranfer tube into the top port of the cryostat. Crack the cryostat valve just prior to insertion, to purge it of air. Only partially insert the tube, do not seat it.

10. Close the recovery valve on the dewar.

Note: If the cryostat does not already have liquid helium in it you can lower the two ends into the dewars much more quickly then in step 11 and 12.

Note: The helium recovery rate should be closely monitored throughout the transfer process. (10 cfm - one count on the mechanical counter per three seconds or less.)

11. Lower the transfer tube dewar end slowly into the dewar until the pressure begins to increase. (Raise the dewar slowly if you are using a rigid transfer line.)

12. The pressure in the crystat will increase as the transfer tube is continued to be lowered into the dewar. It should remain high for a minute or two, 15-25"H2O, and then it will drop rapidly. When this occurs, Insert the cryostat end fully, in order to seat it. The pressure in the dewar will drop somewhat in response. Typical pressures at this point are: Dewar<40"H2O Cryostat<5"H2O.

13. Open the valve on the Pure Helium Supply port and add regulated gas to maintain a stable pressure in the dewar. <40"H2O

14. The pressure in the cryostat will slowly rise to approach the pressure it had while precooling but should be less. Adjust the regulated gas to seek a dewar pressure that results in a cryostat pressure of about 15"H2O. Set the regulator to about 2 psi for a start.

Note: The helium recovery rate should be closely monitored throughout the transfer process. (10 cfm - one count on the mechanical counter per three seconds or less.)

15. When all pressures are stable, note the operating pressures. A sudden jump in cryostat pressure with a vibrating pressure gage needle occurs when the dewar is full.

16. Depending upon how empty the cryostat was, it should be full in about 20 to 30 minutes. Check frequently to verify that the pressures are stable.

17. When the cryostat is full, close the valve from the pressurizing regulator, and open the recovery line on the dewar. These two steps effectively stop the transfer.

18. It will take several steps to raise the transfer tube, since the seals on both dewars will freeze and prevent you from lifting the tubes more than a short distance. Just wait a moment for the seals to warm and the tubes can be raised further. When the end of the tube in the transport dewar is up to the ball valve, stop there and wait several minutes for the pressure to reduce and for all frost to evaporate from the transfer tube assembly. Do not just pull the transfer tubes out in one hurried motion. That is dangerous and wasteful.

19. Raise the transfer tube assembly from the transport dewar just enough to close the ball valve while still keeping the fittings sealed.

20. Disconnect the transfer tube from the cryostat and immediately close its valve. Do not attempt to move the dewar, if the recovery line has frosted. Remove the transfer tube from the transport dewar. Hang the transfer tube in a secure location.

21. When the recovery hose has defrosted, but before moving the dewar, measure its liquid level.

22. Record all "transfer end" information on the transport dewar chart or in the HLD by choosing "End Transfer".

23. Return the transport dewar to a storage area, do not store it in the lab.

24. Be sure to connect it to a recovery port and that the recovery valve is open and all other valves are closed.

25. Plug the cryonet wire into the HLD.

26. Assure that all cryostat fittings are snug and sealed and safe.

This webpage is administered by the
Cryogenic Services at the University of Florida in the Department of Physics
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