Disclosed herein is an inversion unit comprising a housing (2), a reel (4) for a liner partially arranged in the housing (2), and a base assembly (6), the housing (2) being arranged on the base assembly (6), said housing (2) comprising a gas inlet (36), an outlet (8) for the liner, an opening (10) comprising a window (14) and a window locking mechanism (12) for closing and opening the window (14). The window locking mechanism (12) is designed to be manoeuvred into an open position in which the window (14) is open and unlocked and a closed position in which the window (14) is closed and locked. The window locking mechanism (12) is designed as a bayonet catch and comprises a motion link assembly (16) and a matching projection assembly (18), the window locking mechanism (12) further comprising a handle (20) and a hinge (28), the handle (20) being pivotably connected to the hinge (28) wherein one of the motion link assembly (16) or the matching projection assembly (18) is arranged on the window (14) and the other of the matching projection assembly (18) or the motion link assembly (16) is arranged on an edge of the opening (10), wherein the hinge (28) is arranged on the housing (2) and wherein the handle (20) is pivotably connected to the window (14) so that the window (14) can be easily opened and closed in a bayonet catch manner using the handle (20).