A ball valve for an access port for introducing an implement into a pressurised chamber, in which the access port 10 comprises an isolation valve 12 connected in series with the ball valve 14. The ball valve 14 has a ball 18 received within and sealed relative to a spherical socket 16. The ball 18 has a through bore for receiving and sealing against the implement 30 which is to be inserted into the chamber. While the implement 30 is positioned within the through bore of the ball 18, the ball 18 is capable of limited rotation within the socket 16 about two orthogonal axes perpendicular to the axis of the through bore.
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