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+ |
+ !General Remarks |
+ |
+ Handling cryogenic liquids should only be done by trained people. The following instruction are by no means a replacement for a certified cryogenics course. They are meant as a reference for how to handle cryogenics at the Neutron guide hall. \\ |
+ Fear is a bad teacher |
+ and you should always consult a more experienced instrument scientist or [the sample environment team|SampleEnvironment], |
+ if you are in doubt how to handle things correctly. \\ |
+ Please always keep in mind that you are working with boiling liquids which will evaporate rather quickly when exposed to ambient temperatures.\\ |
+ Think about the consequences of your doing __before__ you do it (e.g. what will happen if you open a specific valve). |
+ |
+ For information on how to set up an orange cryostat and how to change samples, please follow this link: [OrangeCryostat|http://lns00.psi.ch/sinqwiki/Wiki.jsp?page=OrangeCryostatCooldownProcedure]. |
+ |
+ !Liquid Nitrogen |
+ |
+ Most of our cryostats and cryo-magnets have an outer liquid nitrogen jacket to reduce the heat load on the helium bath.\\ |
+ The storage dewars are prepared by the sample environment staff and can be picked up at the preparation area (between FOCUS and MARS).\\ |
+ The dewars provided are self pressurizing systems with a mechanical level indicator at the top as shown below.\\ |
+ [LN2_dewar_schematics|LN2.png] |
+ |
+ The dewars are always pressurized. |
+ *Ensure that the hose is firmly connected to the vessel and the nozzle is not pointing towards a person before opening the valve. |
+ The filling hoses have a metallic protection sleeve. The valves and the hose get very cold during a nitrogen transfer. |
+ *Make sure that you wear protective leather gloves when handling cold parts, however the gloves should never be soaked with LN2 or LHe. |
+ |
+ |
+ When using the automatic nitrogen refill |
+ *test the automatic to assure that the filling hose remains in the cryostat filling port and that the system switches off correctly |
+ |
+ !Liquid Helium |
+ |
+ Liquid Helium dewars are provided by the sample environment staff at the preparation area.\\ |
+ At PSI we run a Helium recovery system. |
+ *Please make sure that the dewars are always connected to the recovery line when not in use |
+ *Remember to close the valve on the recovery line when taking a dewar away and to open it after return |
+ *The Level meter in the preparation area shows the level in litres. Make sure that there is sufficient helium for filling. The dewars |
+ should be returned with a level of at least 10-15 litres. |
+ *When using the crane be aware that no equipment (or dewar) should be moved over the DMC detector |
+ |
+ |
+ [LHe_dewar|HeDewar.png] |
+ |
+ __Helium Dewar Transport:__\\ |
+ Helium dewars are brought into the experimental area with the 1T crane. |
+ *Only instructed people are allowed to use the crane. (A short training is offered by the LDM mechanics personal.) |
+ *Only dewars with pre-installed transport straps are allowed for crane transportation. |
+ *To extend the straps please use the proper extensions as shown in the picture below. |
+ |
+ | [transport extensions|HeDewartransport.png] | [dewar with transport fixtures|transportstraps.png] |
+ |
+ |
+ __Helium Transfer:__ |
+ *Before you open the extraction port you should release the pressure in the dewar which might have built up during transport by opening one of the release valves |
+ *Insert the Helium siphon first into the transport dewar. |
+ *close all manual pressure release valves |
+ *slowly lower the siphon into the dewar and observe the pressure rise in the dewar (try to stay below 0.2bar) |
+ *you should see gas streaming out on the other end of the siphon |
+ *don't put your hands in the gas stream |
+ *when it starts to turn white you can insert this end into the cryostat Helium filling port |
+ *continue to lower the siphon into the transport dewar until you reach the bottom. |
+ *switch on the compressed Helium gas line and connect the gas hose to one of the pressure release valves |
+ and open it. The dewar is now pressurized to 0.15 bar over pressure. |
+ *make sure not to empty the vessel completely, the people running the liquefier will love you. On the transfer line, normally there is a prolongation with a hole at 10 cm above the end. If not, you should lift the transfer line by 10 cm after inserting. |
+ When the transfer is finished: |
+ |
+ *stop the pressure line |
+ *release the dewar pressure before you remove the siphon. |
+ *make sure that the extraction and filling ports are properly sealed. It might be necessary to |
+ use a hair dryer to remove the ice. |
+ |
+ [He_gas_line|gasline.png] |
+ |
+ !Returning Liquid Helium Dewars |
+ please return dewars to the dewar station as soon as possible after the transfer |
+ *connect the dewar to the rubber hose of the dewar station |
+ *open the manual valve to the recovery |
+ *open the manual pressure release that is connected to the recovery on the dewar |
+ *check the other manual pressure release. it MUST be closed |
+ *retighten the locking nut of the Helium extraction port |
+ *connect the level probe |
+ |
+ IMPORTANT: |
+ recheck that all valves are in the right state and the level is reading before you leave |
+ [afterfill.png] |
+ |
+ In case you are unsure about certain procedures, please contact sample environment staff |