walls 91 and 93 and the sector door walls 72 and 74 respectively on this shaft 114 between these walls 91 and 93 and parallel to the axis 62 of the door 60 there is connected a toggle link 100 pivoted at one end 102 to the inside of the movable wall 98 and at the other end to the bar 114 this link 100 may comprise a pair of telescopic members 104 and 106 urged apart by an interior helical spring 108 see fig iv the action of this spring 108 may be damped by a friction pneumatic or hydraulic mechanism to prevent noise when this spring pushes the movable wall 90 into its two extreme positions shown in figs iv or v and vii or viii respectively it is to be noted that this particular outwardly urged spring link 100 acts as a toggle mechanism in these two most extended positions in all other positions of the toggle link 100 such as shown in figs vi and ix the toggle link 100 is more compressed and the rod 114 to which it is connected is at the opposite end of the slots 94 from what it is when the link 100 is in its fully extended positions shown in figs iv and viii the third part of the closure 50 or 52 that moves both with and relative to the door 60 comprises a lever 110 pivoted to the door 60 on the shaft 112 parallel to and near the pivotal axis 62 of the door 60 connected to one end of the lever 110 is the shaft 114 that slides back and forth in the slot 94 of the movable pocket wall.