Rotating machine

A pump comprising a casing and an impeller which is rotatable relative to the casing, the impeller being positioned relative to an aperture in the casing such that an annular gap is formed adjacent the aperture between a first surface defined by the impeller and a second surface defined by the casing, wherein a screw thread is formed on at least one of the first and second surface such that material entering the gap is progressively ejected therefrom as a result of interaction with the surfaces, thereby preventing the accumulation of material within the gap.

A rotating machine comprising a casing and a rotor which is rotatable relative to the casing, the rotor being positioned relative to an aperture in the casing such that an annular gap is formed adjacent the aperture between a first surface defined by the rotor and a second surface defined by the casing, wherein a screw thread is formed on at least one of the first and second surfaces such that material entering the gap is progressively ejected therefrom as a result of interaction with the surfaces, thereby preventing the accumulation of material within a gap, wherein the thread has a depth of from 1 to 2 mm and a pitch of from 1 to 3 mm.

A rotating machine comprising a casing and a rotor which is rotatable relative to the casing, the rotor being positioned relative to an aperture in the casing such that an annular gap is formed adjacent the aperture between a first surface defined by the rotor and a second surface defined by the casing, wherein a screw thread is formed on at least one of the first and second surfaces such that material entering the gap is progressively ejected therefrom as a result of interaction with the surfaces, thereby preventing the accumulation of material within the gap, wherein the spacing between the first and second surfaces is such that the minimum clearance between those surfaces is from 0.5 to 1.5 mm.