Device set of a closure system for a shaft construction which can be closed by a shaft cover, the device set comprising: a) a closure for opening and closing a partial volume which can be separated from the remaining shaft volume; b) a mount which can be installed in the shaft construction and which is designed to receive the closure; c) a closing unit which has a locking position and a release position with which the closure can be locked or released in the mount so that it can be mechanically fixed in the locked state in the mount, the closing unit comprising a movable latch and a locking device, the latch being able to engage in the locking device and, in the locking position, fixing the closure in the mount, and d) a locking unit for a shaft cover, wherein the locking unit can be in a locking position and in a neutral position, and wherein the locking unit is designed in such a way that, in the mounted state, in the locking position it prevents complete closing of a shaft cover, while in the neutral position it allows complete closing of the shaft cover; wherein the locking unit can be coupled to the closing unit in such a way that a movement of the locking unit into the neutral position is only possible when the closure is locked, wherein: - the locking device has a movable element which is movable between a closed position and an open position, and - the locking device is designed in such a way that, when the closing unit is unlocked, the movable element executes a defined movement into the opening position as a result of the action of the latch moving during unlocking, and - the locking unit has a locking element which is movably mounted in a guide and can be moved between a locking position and a neutral position, and - the movement of the locking element in the locking unit is mechanically coupled to the movable element in the locking device, such that upon movement of the movable element from the closed position to the open position, the locking element of the locking unit is moved from the neutral position to the locked position, characterized in that the locking unit can be coupled to the closing unit in such a way that when the closure is released, the locking unit is moved into the locking position. a) a closure for opening and closing a partial volume which can be separated from the remaining shaft volume; b) a mount which can be installed in the shaft construction and which is designed to receive the closure; c) a closing unit which has a locking position and a release position with which the closure can be locked or released in the mount so that it can be mechanically fixed in the locked state in the mount, the closing unit comprising a movable latch and a locking device, the latch being able to engage in the locking device and, in the locking position, fixing the closure in the mount, and d) a locking unit for a shaft cover, wherein the locking unit can be in a locking position and in a neutral position, and wherein the locking unit is designed in such a way that, in the mounted state, in the locking position it prevents complete closing of a shaft cover, while in the neutral position it allows complete closing of the shaft cover; - the locking device has a movable element which is movable between a closed position and an open position, and - the locking device is designed in such a way that, when the closing unit is unlocked, the movable element executes a defined movement into the opening position as a result of the action of the latch moving during unlocking, and - the locking unit has a locking element which is movably mounted in a guide and can be moved between a locking position and a neutral position, and - the movement of the locking element in the locking unit is mechanically coupled to the movable element in the locking device, such that upon movement of the movable element from the closed position to the open position, the locking element of the locking unit is moved from the neutral position to the locked position, characterized in that the locking unit can be coupled to the closing unit in such a way that when the closure is released, the locking unit is moved into the locking position.