A turbomachine comprising: a casing having an interior chamber (Cc) and an annular wall section (16; 86a) defining a casing opening (Oc) into the interior chamber and having an outer circumferential surface; characterised in that a closure device engageable with the casing and including a closure body having an inner circumferential overlap surface defines a body opening (O B), the closure body being configured to receive at least a portion of the casing annular wall section within the body opening such that the closure body overlap surface extends about the annular wall section outer surface to close the casing opening, the casing annular wall section includes a circumferential groove extending radially inwardly from the outer circumferential surface and circumferentially about a central axis, and the closure body includes a circumferential groove extending radially outwardly from the inner circumferential surface; the closure device comprises a plurality of retainers engageable with the casing and configured to retain the closure body coupled with the casing so as to prevent displacement of the closure body relative to the casing in a direction along the central axis, each retainer including an arcuate body having an outer circumferential portion disposed within the closure body circumferential groove and an inner circumferential portion disposeable within the casing circumferential groove; and the closure device includes a plurality of positioners configured to displace the retainer arcuate bodies radially with respect to the closure body so as to advance the retainer arcuate bodies into the casing groove and to alternatively withdraw the retainer arcuate bodies from the casing groove; wherein the closure body includes a separate counterbore hole for each positioner, each retainer includes at least one threaded opening, and each positioner includes a threaded rod, having a first end disposed within the counterbore hole and a second end threadably engaged within the retainer opening. a casing having an interior chamber (Cc) and an annular wall section (16; 86a) defining a casing opening (Oc) into the interior chamber and having an outer circumferential surface; characterised in that a closure device engageable with the casing and including a closure body having an inner circumferential overlap surface defines a body opening (O B), the closure body being configured to receive at least a portion of the casing annular wall section within the body opening such that the closure body overlap surface extends about the annular wall section outer surface to close the casing opening, the casing annular wall section includes a circumferential groove extending radially inwardly from the outer circumferential surface and circumferentially about a central axis, and the closure body includes a circumferential groove extending radially outwardly from the inner circumferential surface; the closure device comprises a plurality of retainers engageable with the casing and configured to retain the closure body coupled with the casing so as to prevent displacement of the closure body relative to the casing in a direction along the central axis, each retainer including an arcuate body having an outer circumferential portion disposed within the closure body circumferential groove and an inner circumferential portion disposeable within the casing circumferential groove; and the closure device includes a plurality of positioners configured to displace the retainer arcuate bodies radially with respect to the closure body so as to advance the retainer arcuate bodies into the casing groove and to alternatively withdraw the retainer arcuate bodies from the casing groove; wherein the closure body includes a separate counterbore hole for each positioner, each retainer includes at least one threaded opening, and each positioner includes a threaded rod, having a first end disposed within the counterbore hole and a second end threadably engaged within the retainer opening.