2.4.2 Vessel 3 to sample cell
The transfer of liquid from Vessel 3 to the sample cell is brought about by the
difference in pressure between that in the Vessel and a vacuum in the cell. However,
in order to control the transfer of liquid the pressure difference should be as small as
possible but not so low that the liquid starts to boil.
•
Switch the pump to its roughing mode.
•
Open values V2 and V3 along with tap C and carefully open valve V1 until a
suitable pressure is obtained (~0.5 bar).
•
Close tap C and continue to evacuate the system and sample cell by opening
valves V3, V4, V5 and V8. Switch the pump to turbo mode.
•
When the required level of vacuum has been obtained, close valves V4 and V5
in order to isolate the sample cell.
•
Opening tap D on Vessel 3 will cause the liquid to move rapidly to fill the
volume between tap D and V5.
•
Valve V5 can be opened carefully in order to allow the liquid into the sample
cell. The movement of liquid can be monitored using the sight glasses
positioned either side of the sample cell.
•
When it is judged that sufficient liquid has been transferred to fill the sample
cell, close valve V5.
At this point, it must be remembered that the lower manifold contains liquid, which
must be removed before the system is evacuated.
2.4.3 Recovery of liquid in manifold to Vessel 2
After the transfer of liquid to or from the sample cell, some liquid will remain in the
pipes of the lower manifold. This can be removed using the following procedure.
•
Vessel 2 should be under vacuum prior to the loading of the liquid into the
sample cell. If it is not, switch the pump to roughing mode and open tap E
followed by valves V1 and 2. If Vessel 2 already contains some liquid ensure
that it is frozen using liquid nitrogen before evacuation is attempted.
•
When the vessel is evacuated close tap E and cool the glass bulb by raising a
dewar of liquid nitrogen around it.
•
Ensure that taps A, B, C, D and E are closed before opening valves V6 and
V8.
•
Opening valve V7 will allow any liquid present in the manifold to enter Vessel
2 where it will freeze.
•
Close valve V7 and repressurise the system and Vessel 2 by opening valve V9
and tap E. Remove the dewar from around the vessel and allow the liquid to
thaw.
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