TURBOMOLECULAR PUMP

PURPOSE:To spread the exhaust-enable range of a pump to the lower vacuum side by forming a spiral groove in the opposite direction to a spiral groove on a screw rotor, onto the inner peripheral surface of the peripheral wall surrounding the screw rotor, and increasing the compression-ratio increasing function for the screw rotor part. CONSTITUTION:On a screw rotor 5, not only a spiral groove 5a formed onto the outer peripheral surface, but a spiral groove 7a in the opposite direction to the spiral groove 5a is formed onto the peripheral wall surrounding the spiral groove 5a, keeping a minute gap, namely onto the inner surface of a spacer 7 fitted onto the inner peripheral surface of an outer frame 6 in the application drawing. Therefore, the spiral grooves 5a and 7a cross each other at each position turning by 180 deg., and the combined body parts 8a, 8b... constituted of the combined spaces of the grooves 5a and 7a are formed at the above-described positions as shown in the figure. These parts 8a, 8b... speedily revolve and lower to an exhaust port B side as the screw rotor 5 revolves at a high speed, and the combined body part pushes-out gas particles very strongly. Therefore, the exhaust speed efficiency is increased in comparison with the conventional.