roughing pump
Roughing pumps make up the first stage of pumping in an UHV system. The work in the pressure regime where there is still a “normal” gas flow. They do not work down to a pressure of 10-9 mbar or 10-9 mbar mbar but not in the UHV regime. Essentially, all types of roughing pumps work in the same way: the volume of the system is expanded in the pump. Then the expanded volume in the pump is sealed off and the gas inside this volume is removed from the system. This process is repeated in cycles.
Common types of roughing pumps are rotary vane pumps, scroll pumps and diaphragm pumps. Rotary vane pumps are particularly popular but have the disadvantage of being oil-sealed with the potential risk of the oil getting into the vacuum system.
Roughing pumps are often very powerful pumps. A common (and very bad) mistake is to attach them to the system the wrong way, i.e. by swapping gas inlet and exhaust. This can be very dangerous since the overpressure in the system can blow out the viewports which can sustain a big pressure difference only in one direction.
