VARIABLE GEOMETRY TURBINE

A variable geometry turbine having a turbine wheel, an inlet passageway, a movable wall member being moveable axially to vary the width of the inlet passageway, an annular seal being mounted to the movable wall member or an adjacent housing member to provide a seal between adjacent surfaces of the movable wall member and housing member respectively, wherein a bypass passage is provided in the other of said movable wall member or housing member, extending from an inlet bypass port to an outlet bypass port, said ports being spaced from each other and provided in said adjacent surface of said other of the movable wall member or housing member, arranged such that as the movable wall member moves axially, the annular seal moves axially relative to the ports to vary the flow that may pass from a region of the cavity inboard of the seal, through the bypass passage.