Cornell High Energy Synchrotron Source
Doc#: SOP-OPS-010	Procedure: Filling large LN2 dewars			Prepared by: KM
Rev.: 1	Revision Date: 04/30/2013	Date Effective: 04/30/2013	Date Expires: 04/30/2014	Approved by:

Purpose
To fill a large liquid nitrogen dewar
Materials and Equipment Needed

1. Large LN2 dewar
2. Face shield (located at LN2 filling station)
3. Gloves safe for cryogenic use (located at LN2 filling station)
4. Large crescent wrench (located at LN2 filling station)

Safety

1. High pressure gas and cryogenics. Wear face shield and gloves
2. Monitor the tank while filling –do not walk away from the area

Reference
Pressure Builder: There is a valve labeled “P.B” on the dewar. This is the pressure builder valve. The PB valve should be closed while filling the tank and while the tank sitting and not being used. For use with the 5 element Solid State Detector, it will probably not be necessary to ever open the PB valve. The dewar should be able to build enough pressure by simply sitting with LN2 in it.
Procedure

1. Connect the vent hose to the “vent” valve on the dewar. Tighten with crescent wrench.
   1. When facing the LN2 filling station, the vent hose is to the right near the floor. The hose goes outside of the building.
2. Open the vent valve on the dewar
   1. It does not need to be opened all the way (although it can be opened all the way). If it is open all the way, it may be very loud. If it is not open as much, it will be quieter but take longer to vent.
3. Connect LN2 filling hose to “liquid” valve on dewar while tank is venting. Tighten with crescent wrench.
   1. When facing the LN2 filling station, the LN2 filling hose is located on the left side.
4. Let the tank vent until the pressure is below 20PSI
   1. Pressure gauge is located on dewar next to “vent” valve
5. Open the “liquid” valve on the dewar when the pressure in the tank is below 20PSI
6. Open the LN2 valve on the wall to start filling the dewar
7. Fill the dewar about ¾ full
   1. There is a gauge on top of the dewar that indicates the LN2 level. It may be necessary to shake the tank periodically while filling to ensure the gauge is not stuck.
8. Close the “vent” valve on the tank
9. Close the LN2 valve on the wall
10. Close the “liquid” valve on the dewar
11. Immediately loosen the LN2 filling hose from the dewar to vent it
    1. Do not remove the hose completely. As soon as it is loosened, it will start to vent.

WARNING: Pressure will build in the LN2 filling hose when both the “liquid” valve on the dewar and the LN2 valve on the wall are closed. Do not leave the hose connected and tight on both ends with both valves closed. As soon as the hose is loosened slightly it will start to blow off. Do not have your face or bare skin near the hose – liquid nitrogen may spit out.

1. Disconnect the vent hose from the dewar while the LN2 filling hose is venting.
2. Disconnect the LN2 filling hose from the dewar when there is no longer liquid or gas blowing off from the hose.

Revision History
Rev. 1 – Initial document (04/30/2013 KM)

-- LeeShelp - 30 Aug 2017