Maintenance 50 Liter Dewar Fill with Cryogens

Check 3.8 liter dewar level

1. When the 3.8 liter dewar level approaches 10 percent an automatic fill from the 50 liter dewar will attempt to start. Check the 3.8 liter dewar level. If it is less than 15 percent then initiate a manual fill and fill to at least 25 percent so that an autofill does not start while you are refilling the 50 liter dewar.
2. If the 3.8 liter dewar is more than 15 percent full proceed to part B below.

Refill the 50 liter dewar

1. Connect liquid transfer line between liquid valve on the 170 liter dewar and liquid valve on the 50 liter dewar.
2. Close HIRES valve on the 50 liter dewar.
3. Open vent valve on 50 liter dewar.
4. Open liquid valve on 50 liter dewar.
5. SLOWLY open liquid valve on 170 liter dewar.
6. Continue filling the 50 liter dewar until LN2 begins to squirt continuously from the 50 liter dewar vent. You can monitor the fill from the analog gauge on the 50 liter dewar electronics.
7. Close liquid valve on the 170 liter dewar.
8. Close liquid valve on the 50 liter dewar.
9. When the pressure on the 50 liter dewar has dropped to zero psi, close the 50 liter dewar vent valve.
10. Open HIRES valve on the 50 liter dewar.
11. Disconnect liquid transfer line between liquid valve on the 170 liter dewar and liquid valve on the 50 liter dewar.

Have you left things in an operational state?

1. HIRES valve on the 50 liter dewar is OPEN.
2. Vent valve on the 50 liter dewar is CLOSED.
3. Liquid valve on the 50 liter dewar is CLOSED.

Revision History:

• 2001 March12
• scd 2002 September 9 Format update