To operate properly, sprinklers have to be in the correct position or orientation. Otherwise, most of the water will bounce off the ceiling, creating a poor spray pattern at floor level and changing the size of the droplets.
A pendent sprinkler hangs down from the water pipe. The water stream flows downward against the deflector.
An upright sprinkler extends up from the water pipe. The water stream flows upward against the deflector.
A sidewall sprinkler is for installation where construction or other special considerations make it necessary to put sprinklers near a wall. A sidewall sprinkler has special deflectors that discharge most of the water away from the wall in a pattern resembling a quarter of a sphere, with a small amount of water aimed at the wall behind the sprinkler.