Gas friction pump

A pump assembly, comprising:

• a turbomolecular pump having a rotor, a stator surrounding the rotor, and a fore-vacuum side;
• and
• a gas friction pump arranged at the fore-vacuum side of the turbomolecular pump and comprising:
• a housing having a suction port and a discharge port;
• rotor means located in the housing and formed of a plurality of coaxial first cylindrical elements;
• and
• stator means located in the housing and formed of a plurality of second cylindrical elements coaxial with first cylindrical elements and surrounding respective first cylindrical elements,
• wherein ones of the first cylindrical elements and the second cylindrical elements have smooth inner and outer surfaces, and another ones of the first cylindrical elements and the second cylindrical elements have a plurality of parallel discharge channels formed on inner and outer surfaces of the another ones of the first and second cylindrical elements, arranged one beneath another and separated by a respective plurality of webs, the parallel discharge channels defining a plurality of parallel discharge chambers forming a plurality of parallel operating pumping chambers for pumping gas from the suction port to the discharge port,
• wherein the pumping chambers pump gas in a single axial direction to the discharge port, and
• wherein both the rotor of the turbomolecular pump and the rotor of the gas friction pump are arranged on a common shaft.

A gas friction pump, comprising:

• a housing having a suction port and a discharge port;
• rotor means located in the housing and formed of a plurality of coaxial first cylindrical elements;
• and
• stator means located in the housing and formed of a plurality of second cylindrical elements coaxial with the first cylindrical elements and surrounding respective first cylindrical elements;
• wherein ones of the first cylindrical elements and the second cylindrical elements have smooth inner and outer surfaces, and another ones of the first cylindrical elements and the second cylindrical elements have a plurality of parallel discharge channels formed on inner and outer surfaces of the another ones of the first and second cylindrical elements, arranged one beneath another and separated by a respective plurality of webs, the parallel discharge channels defining a plurality of parallel discharge chambers forming a plurality of parallel operating pumping chambers for pumping gas from the suction port to the discharge port, and
• wherein the first cylindrical elements and the second cylindrical elements have different axial lengths, whereby an axial expansion of pumping elements which are formed by the first and second cylindrical elements, decreases from inside out.