An improved vacuum pump mechanism is described in which an intersecting solid or perforated element is arranged to intersect a channel member. Relative movement of the intersecting solid or perforated element and channel member causes gas molecules to be urged from inlet to an outlet of the pump. Gas molecules are constrained within the channel member and interaction of the gas molecules with the flat and smooth surfaces of the intersecting solid or perforated member influence momentum of the gas molecules so that they are directed towards the outlet. In one embodiment, the channel member is formed as a helix and the intersecting solid or perforated elements are disk-shaped. An alternative embodiment is provided having the channel member configured as a spiral and the perforated elements as cylindrical skirts. The pump provides significant improvements in pump capacity, reduced power consumption and size of pump.