A valve assembly comprises a conduit having a throughbore and defining a longitudinal axis, a sealing member that is moveable between an open configuration in which the throughbore of the conduit is open, and a sealing configuration in which the sealing member is arranged to substantially obturate the throughbore of the conduit, wherein in the sealing configuration, the sealing member seals the throughbore along a sealing line at least a part of which is angled relative to a direction perpendicular to the axis of the throughbore.