Turbomolecular pump

In an integral high vacuum pump including a generally cylindrical outer pump housing having an axis, an axial turbomolecular compressor and a peripheral compressor, each said compressor having a rotating portion, said rotating portions of both said compressors being coaxial to and coupled to a single high speed motor drive shaft aligned along said axis, the improvement comprising:

• said peripheral compressor being a serial combination of a two section pump, said first section being a molecular and transient flow region pump and said second section being a viscous flow pump, whereby the serial combination of said axial flow turbomolecular compressor and said peripheral compressor provide, in operation, an ultimate vacuum pressure of a least 10.sup.-7 Pascal when exhausting at atmosphere pressure;
• said first section of said peripheral compressor being completely enclosed and isolated by a first closed casing mounted to said outer pump housing, except for an inlet and exit orifice, and except for leakage at said drive shaft;
• and
• said second section of said peripheral compressor being completely enclosed and isolated, by a second closed casing mounted to said outer pump housing except for an inlet and exit orifice, and except for leakage at said drive shaft;
• and
• said first and second casings being axially separated by an expansion chamber, said expansion chamber being formed and bounded by said cylindrical outer pump housing, said first closed casing and said second closed casing.