Vacuum control device for the displacement of an element between at least three positions

A vacuum control device for the displacement of an element between at least three positions, comprising a casing in which are disposed at least two spaced substantially parallel movable cups, said casing having a bottom end-wall, the first cup being connected to the element to be displaced, said second cup being spaced from said bottom end-wall, springs interposed respectively between the two cups and between the second cup and said bottom end-wall of the casing, and two fluid communication means adapted to be connected to a vacuum source and to atmospheric air and opening into the casing respectively within the space located between the two cups and within the space located between the second cup and the bottom end-wall of the casing, a deformable flexible diaphragm carrying said first cup and having a periphery attached to the casing and providing a leak-tight division of the internal space of said casing said second cup being mounted within the casing with a clearance and in a non-leaktight manner for movement toward and away from said end-wall, said casing including a fixed portion remote from said bottom end-wall, the associated spring resiliently biasing said second cup into sealing engagement against said fixed portion, thereby dividing the internal space of the casing into two space chambers which are separated in leak-tight manner the two space chambers communicating with each other upon movement of the second cup away from said fixed portion.