It is an air gap that allows air to escape rather than building up in the pipe and creating an air hammer within the pipes (banging noise), and problems with drainage. (think about pouring out of a can that doesnt have the second hole punched in it.
Suction Therapy : Suction therapy is provided to assist in the removal of bronchial secretions that cannot be expectorated by the patient spontaneously. Suct...
There is no compression in correctly performed suction cup therapy. Although it is quite common during Stationary Dry Cupping (left static for 5 - 20 minutes - see below) to achieve dramatic 'marks' or 'discolorations', the less aggressive action of moving the cups, minimizes the intensity and duration of the discolorations.