The top picture shows a typical setup for a vacuum line. It consists of a glass manifold, which is connected to a vacuum pump and an inert gas supply e.g. nitrogen or argon. The pictures below show the two 'settings' for the stopcocks in the glass manifold.

1. The vacuum part of the Schlenk line is connected to a low-temperature trap to protect the pump from harmful vapors. It has to be submerged in a Dewar container with liquid nitrogen (or an isopropanol/ dry ice bath), when the pump is running. The line has to be closed before the Dewar container is filled with liquid nitrogen to prevent the condensation of air. Condensed air can cause heavy explosions. Once the cooling source is removed, the liquefied air will evaporate very fast and causes an overpressure in the system. Also, nitrogen has a lower boiling point than oxygen. Liquid oxygen will stay behind and react violently with any organic materials collected in the trap. When you turn off the pump, you will have to vent it immediately. The Dewar with liquid nitrogen has to be removed at this point. Liquid nitrogen has a temperature of -196^oC and causes severe burns.

2. The pumps in the laboratory are mechanical pumps. They employ a rotor that revolves inside a cylindrical stator. A thin film of oil maintains a seal between fixed and moving parts. Therefore, it is imperative that other materials do not contaminate the oil. The vacuum that can be reached with these pumps is in the range of 10^-2 torr.

3. The inert gas part of the Schlenk line is connected to a tank of nitrogen or argon. At the end of the line, a pressure release bubbler is attached to monitor the pressure in the inert gas line. Whenever you plan to do manipulations on this part of the line, make sure that you have a positive pressure in the line. If you have to refill glassware with larger volumes, do the refilling stepwise. If you just open the stopcock, the pressure in the inert gas line will drop to ~10^-1-1 torr. Small leaks will generate major problems then. If you are handling very sensitive materials, make sure that your line is air free.

4. A stopcock has two pathways to connect both parts of the manifold. Depending on the orientation, it connects the vacuum line or the inert gas line to your setup. Make yourself familiar with them. It might be a good idea to 'color code' them to avoid confusion.

5. Several people are using the same inert gas line. You need to coordinate your work (refilling flame-dried glassware, filtrations, transfers of solids or liquids, etc.) with your fellow students in order to prevent major accidents from occurring. Nobody will not be happy to find her/his solution in the inert gas line, because somebody refilled a large volume at one time and his refluxing setup bumped into inert gas line. Contamination of the line with other (corrosive/reactive) gases like ammonia, chlorine, etc should be avoided as well.