HD Vertical Sidewall Sprinkler is a small, thermosensitive, glass-bulb spray sprinkler available as standard or quick response type in temperature ratings to meet design requirements. Sprinkler is UL Listed. During fire, the heat-sensitive liquid in the glass bulb expands, causing the glass bulb to shatter. Water flowing through the sprinkler orifice strikes the sprinkler deflector, forming a spray pattern in order to control or extinguish fire. HD vertical sidewall sprinklers are designed for use in light and ordinary hazards for standard installation. The design provides a crescent-shaped water discharge pattern.