Folding lid stairs are preferred when the ceiling of the basin is not yet built, they occasionally with heavy vehicles are driven on and an easy to handle,but
appropriately resilient cover (in non-moving traffic) is desired. At the same time, they offer advantages in Basin cleaning with flushing tilts and surge flushing systems because the stairs during the rinsing process not at the bottom of the basin, but below the ceiling.
When the lid is closed, the staircase hangs between Building ceiling and max. water level. Via a lever geometry the staircase is connected to the cover in such a way that it can be used as a counterweight when the lid is opened.