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 first and second 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 separate flexible and deformable diaphragm carrying each cup and having a periphery attached to the casing and providing a leak-tight division of the internal space of said casing, the diaphragm which carries the second cup including a central portion with a base thereon, said base supporting the spring interposed between the two cups, said casing including a fixed portion remote from said bottom endwall of the casing, the spring interposed between the second cup and the bottom end-wall biasing said second cup and base to engage said base against said fixed portion and define a fixed position for said second cup.