NW25 Heated foreline traps
NW25 S/S Heated inlet trap, with Alumina. This type of trap is to prevent oil vapour that moves out of the pump inlet under low pressure conditions when the gas is in molecular flow. That would be at a pressure lower than about 0.1 Mbar. The ultimate vacuum of an oil sealed vacuum pump is reached when the hot oil in the pump starts to evaporate. Under these conditions some molecules of oil vapour will backstream from the pump inlet toward the vacuum system. Although back streaming of oil vapour occurs in larger pumps as well, it can be more critical in smaller vacuum systems where the piping is shorter. Instruments such as mass spectrometers, electron microscopes and ultra-high vacuum systems can be contaminated if oil vapour reaches them so most of these instruments use foreline traps. If these instruments become contaminated it can take several days to clean them out and return them to operation.