By alternately conducting pressure fluid into cylinder through its three holes the pink piston can reach one of its three stable positions: center, left and right.

Green and blue floating pistons are identical. The arrows show flows of pressure fluid.

When pressure fluid enter through the medium hole, green and blue pistons are pushed apart from each other, pink piston gets center position.

When pressure fluid enter through the left hole, pink and blue pistons are pushed to the right, pink piston gets right position.

When pressure fluid enter through the right hole, pink and green pistons are pushed to the left, pink piston gets left position.