Filling procedure of 190 liter LN2 Dewar

Anders Liljeborg, 2014-08-29
Updated, moved behind AJA2 system, 2015-10-20
Updated, filling at RT, 2016-04-01

You must get safety instructions from the workshop personel before being allowed access to the LN2 filling station.

  


There are three valves at the top of the Dewar:
  1. Blue valve, inlet/outlet valve, used for tapping off LN2 and refilling
  2. Green valve, used for pressurizing the Dewar
  3. Grey valve, outlet for boil-off, used for depressurize the Dewar

  1. Close all valves.

  2. The scale is no longer used, the support screws should always be upwards!

  3. Disconnect the tube from the blue valve (2). Note! Unscrew the bigger (½ inch) Swage-lok connector, see picture below.


    Disconnect the tube at the ½ inch Swage-lok connector. Use two spanners to unscrew the indicated parts.

  4. Disconnect the battery charger from the scale. It should aready be disconnected since the scale is not used anymore.

  5. Carefully roll Dewar to LN2 room. It is located at the goods reception.

  6. Bring the extra ½ inch tube to connect Dewar the LN2 outlet.


    Tube with ½ inch Swagelok connectors. The isolation is to avoid frosting when filling LN2.

  7. Bring two spanners for tightening Swage-lok connectors.

  8. Position the trolley near the left hand outlet.

  9. Connect the isolated ½ inch tube you bring to the tube attached to the left outlet.


    The filling station.
    The left hand tube and left valve is used for filling the 200 liter dewar.

  10. Open grey valve (4) fully (valve for boil off).

  11. Open blue valve (2) fully (inlet valve).

  12. Open the left hand valve of the filling station.

  13. There will be much boil-off, especially if the Dewar is completely empty and at room temperature.

  14. Slowly open the valve on the filling station until fully open.

  15. If the dewar is at room temperature, i.e. completely empty, always fill a few liters, then close the valve of the filling station and wait 30 minutes for the Dewar to cool down. This avoids water (humidity) to form ice inside the dewar fill valve. It will also reduce the boil-off.

  16. Stop filling when there is droplets of LN2 coming out of the grey valve (4). Then the dewar is completely full (about 200 liters).

  17. The level indicator should be higher than midway between the marks.

  18. Close the valve on the filling station

  19. Close the blue valve (2).

  20. Check the manometer, it should read zero. If it is showing some pressure, wait until it goes down to zero.

  21. Close the grey valve (4).

  22. Carfully disconnect the tube you brought from the tube permanently connected to the filling station. Unscrew it a little to let the LN2 within the tube boil off before you fully disconnect. It will boil off within a minute.
    Let it be attached to the blue valve (2).

  23. Note how many liters you have filled on the form on the wall cabinet.

  24. Carefully roll the Dewar back to the lab. Note! it is 120 kg heavier now.

  25. Connect the Dewar to the CryoRIE as before.

  26. Pressurize the Dewar using the green valve (3).

  27. Wait until the manometer reads 4 Bars, then close the green valve.

Detailed list, compressed, without pictures

  1. Close all valves.
  2. Check that the support screws for the scale platform are tightened upwards, thereby securing the scale from vibration damage.
  3. Disconnect the tube from the blue valve (2). Note! Unscrew the bigger (½ inch) Swage-lok connector, see picture below.
  4. Carefully roll Dewar to LN2 room.
  5. Bring the extra ½ inch tube to connect Dewar the LN2 filling station located at the goods reception.
  6. Bring two spanners for tightening Swage-lok connectors.
  7. Position the trolley next to the left valve of the filling station, the one with a ½ inch tube already attached.
  8. Connect the isolated ½ inch tube to the blue valve and to the ½ tube on the filling station.
  9. Put on the insulating gloves which are present in the LN2 generator room.
  10. Open grey valve (4) fully (valve for boil off).
  11. Open blue valve (2) fully (inlet valve).
  12. Open the left valve on the filling station.
  13. There will be much boil-off, especially if the Dewar is completely empty and at room temperature.
  14. It can be good to fill a few liters, then wait 30-60 minutes for the Dewar to cool down. This will reduce the boil-off.
  15. Slowly open the left valve on the filling station until it is fully open.
  16. The level indicator should be higher than midway between the marks and/or droplets of LN2 come out of the grey valve (4).
  17. Close the valve on the filling station.
  18. Close the blue valve (2).
  19. Check the manometer, it should read zero. If it is showing some pressure, wait until it goes down to zero.
  20. Close the grey valve (4).
  21. Disconnect the tube from the tube at the filling station.
    Take care that trapped LN2 can boil off by partly unscrewing the connection. Let it be attached to the blue valve.
  22. Note how many liters you have filled on the form on the wall cabinet.
  23. Carefully roll the Dewar back to the lab. Note! it is 120 kg heavier now.
  24. Connect the Dewar to the CryoRIE as before.
  25. Pressurize the Dewar using the green valve (3).
  26. Wait until the manometer reads 4 Bars, then close the green valve.

Support screws for scale platform, scale no longer used.


Two of the support screws that secures the scale platform during transport.
They should be tightened upwards before moving the trolley.


Close up of left support screw. Note that it is the upper screw head that should be turned to tighten against the upper grey metal bar.


Close up of right support screw.


The support screws on the other side of the scale.

Anders Liljeborg Nanostructure Physics, KTH.