A control arrangement (34) for controlling the size of a gap (30) between first and second components. The control arrangement comprises first magnet means (38) to be provided on the first component, and second magnet means to be provided on the second component. The first and second magnet means are in magnetic interaction with each other across the gap (30) and the arrangement further includes control means (36) to control the size of the gap (30) the first magnet means (38) is a moveable in a first direction to cause the control means (36) to effect relative movement of the first and second components to increase the gap (30) and in a second direction to cause the control means (36) to effect relative movement of the first and second components to decrease the gap (30). The first and second magnet means are arranged such that relative movement of the first and second components towards each other moves the first magnet means (38) in the first direction, and relative movement of the first and second components away from each other moves the first magnet means (38) in the second direction.