A variable geometry turbine having an annular inlet passageway defined by a radial surface of a first wall member mounted within a cavity. The first wall member is axially movable to vary the size of the inlet passageway. There is also a second wall member, which covers the opening of a cavity defined by the housing. The second wall member comprises an outer flange 127 defining a circumferential flange groove for receiving a retaining ring for securing the second wall member in the cavity. An array of inlet guide vanes 114 extend across the annular inlet passageway to define a radial vane passage, the radial wall 124 of the second wall member defining a radial second surface that opposes the first surface, wherein the second wall member further comprises an annular flange 162 that extends axially into the cavity and which supports a radially extending flange 163 that defines a radial third surface that is opposed to the radial second surface. This pressure balancing flange 163 allows the pressure in the cavity to produce an axial force on the second wall member and reduces the vibration on the second wall member, thus reducing the wear and fatigue.
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