The SAV is designed to conserve the diver's air while on the surface. This is Not a snorkel. Generally, when diving with a full-face mask, the diver is breathing off a scuba bottle or surface supplied air. With the SAV, the diver can breathe ambient air without removing his/her FFM. Operating the SAV is simple. If you rotate the valve counterclockwise, you will breathe ambient air. If you have the valve rotated fully clockwise, it will be closed, and you will breathe off your supply air.