Outline • Starting Up • Shutting Down • Cleaning Manifold • Changing Pump Oil • Dealing with Liquid O2
Starting Up PPE Needed: Lab Coat, Gloves, Safety Goggles/Glasses 1. Ensure that the manifold stopcocks, as well as all seals, are properly greased. 2. Check to see that the vacuum trap is dry and clean. 3. Make sure that there is enough Liquid N2 on hand to fill the dewar. 4. Insert traps into empty dewars. 5. Ensure that all valves are closed, and start or open line to the vacuum pump. 6. Fill the dewar with liquid nitrogen. Wrap the top with a towel, cotton, glass wool, or aluminum foil. 7. Watch the gauge to ensure that the pressure is dropping.
Notes for Starting Up • Depending on whether you have one or two traps, you will have to refill the dewar(s) every 6-8 or 12 hours, respectively. • Make sure the system is under vacuum while any portion is under liquid nitrogen. Otherwise, oxygen could condense, which could result in a serious explosion (see below).
Shutting Down PPE Needed: Lab Coat, Gloves, Safety Goggles/Glasses 1. Remove the Liquid N2dewar. 2. Shut off vacuum pump and vent the manifold. 3. Once the dewars are taken down, allow the system to thawto room temperature before safely disposing of any solvents.
Notes for Shutting Down • Never vent the system to air or turn off vacuum when any portion of the system is still at liquid nitrogen temperature. This could condense oxygen which could result in a serious explosion (see below). Always make sure the liquid nitrogen is removed prior to turning off or venting vacuum.
Cleaning PPE Needed: Lab Coat, Gloves, Safety Goggles/Glasses Supplies Needed: ApiezonM Vacuum grease, Hexanes • Carefully disassemble the system (FRAGILE!) and clean with hexanes, disposing of it in normal organic waste. • If necessary soak glass manifold in base bath (isopropanol with added potassium hydroxide).
Cleaning • Re-grease joints with Apiezon M Vacuum grease (orange tube), using a heat gun to gently heat the joints before applying grease.
Changing Vacuum Pump Oil PPE: Lab Coat, Gloves, Safety Goggles/Glasses Tools and Supplies: Screwdriver, Tygon or Latex Tubing 18-36 inches in length, Gloves, Squirt bottle of hexanes, 4 L bottle of Pump Oil, Empty container for waste oil. 1. Ensure vacuum pump is off. 2. Use screwdriver to disassemble the hose from the pump to the manifold. 3. Unplug and place pump on bench top (HEAVY!) 4. Find an empty oil container or any other 2-4 liter container for pump oil waste. 5. Making sure to attach a latex or tygon tube to the drainage nozzle, open and allow for the oil to empty as much as possible. You may have to tilt the pump to drain all of the oil.
Changing Vacuum Pump Oil, continued 6. Partially fill with fresh pump oil. Seal the top with a vulcanized rubber stopper. Plug in and run the pump for 1 minute. Drain. 7. You may have to re-repeat step 6 depending on how much particulate matter you see in the oil. Otherwise, add fresh oil to the fill line in the pump oil window. 8. Place pump on the floor (HEAVY!) 9. Reassemble the pump and plug in. 10. Done! • The vacuum pump oil should be changed at least every three months or more often depending on use.
What to do if Liquid O2 is Condensed in Trap • Oxygen is characterized by a light blue gas in low concentrations or light blue colored liquid. • It is highly explosive in the presence of organic compounds, including the grease used for the system. • It is a very dangerous situation to have condensed liquid oxygen and should be treated accordingly.
Dealing with Condensed O2 1. If the liquid nitrogen dewar is removed and the liquid in the traps has a blue color or if any liquid is observed, then assume you have liquid oxygen in the trap. • Immediately replace the liquid nitrogen to keep the traps cold. (Note: the longer the liquid nitrogen is there, the more oxygen is condensed. Only do this step very temporally, 1-2 minutes, to get ready to vent the traps as described below; otherwise do not do this.) • Inform others of the situation and evacuate the lab area except for a buddy at a safe distance. 4. Place a blast shield around the traps and remove any nearby organic materials.
Dealing with Condensed O2, cont’d 5. Remove the liquid nitrogen dewar, quickly vent the system, and if possible lower the hood sash completely 6. Immediately leave the vicinity of the lab and warn others not to enter. • After the system has warmed to room temperature consider the traps still dangerous . Liquid oxygen will not be present, but organic peroxides may have formed. Pour liquid into a clean beaker and flush assembled trap 5 times with water. Do this behind the blast shield and with the sash lowered. • Check the solvent for peroxides using a potassium iodide test strip. If a purple color forms on the text paper, peroxides are present. In that case, reduce solution by adding sodium thiosulfate or sodium sulfite before disposing of waster. • As soon as is safely possible, make sure your research director is informed of the situation.
Questions? Ask your research director! Do not solely rely on lab folklore.