Patent ID: 8070419

Claim:
Molecular spiral vacuum pumping stage comprising: a rotor disk ( 7 ; 7 â€²) having smooth surfaces and cooperating with a stator body ( 1 ; 11 ; 21 ), at least on one surface of the stator body facing said rotor disk comprising at least one spiral channel with a cross-section area (Ïƒ), said spiral channel comprising an inlet ( 6 ; 6 â€²) and an outlet ( 8 ; 8 â€²) for pumping gas there through, wherein the cross-section area (Ïƒ) of said at least one channel is reduced from the center to the outer periphery of said stator body ( 1 ; 11 ; 21 ) according to the condition, to be respected within a maximum deviation of Â±10%, where: S = V n Ã— Ïƒ = 2 â¢ Ï€Ï‰ â¢ â¢ H â¡ ( R ) â¢ R 2 â¢ â…† R R â¢ â…† Ï• 1 + [ â…† R R â¢ â…† Ï• ] 2 = CONSTANT , wherein S is the volumetric channel speed V n is half the rotor velocity normal to area Ïƒ, R is the distance from the center of the stator body ( 1 ; 11 ; 21 ); Ï‰=V T /R is the rotor angular velocity; V T is the local velocity of the rotor; H(R) is the height of the channel, possibly variable as a function of R; Ï† is the winding angle of the channel spiral.