Did you know? Sprinkler Head Operation & Types

What types of Sprinkler Heads are available?

Fusible Link Sprinklers vs. Glass Bulb Sprinklers

All wet-pipe sprinklers are held closed by either a fusible link or a glass bulb that contains a heat-sensitive liquid.

A fusible link sprinkler head has a two-part metal element that is fused by a heat-sensitive alloy. The link holds the pip cap, or plug, in place. Once the ambient temperature around the sprinkler head reaches a specified temperature, the alloy releases and the metal elements separate, which causes the pip cap to fall away. Water is then released. Note that water is only released by sprinkler heads where the ambient temperature reaches a specified level – therefore, water is only released in the area of a fire, which helps limit water damage.

Glass bulb sprinkler heads have a small glass reservoir that holds a heat-sensitive liquid. This glass bulb holds the pip cap in place. When the ambient temperature of the liquid reaches a certain level, the liquid expands causing the glass bulb to break, which allows the pip cap to fall away releasing water. As with the fusible link heads, water is only released where the ambient temperature reaches a certain level, which helps limit water damage.

Pendant Sprinkler Head

Pendant sprinkler heads hang down from the ceiling and spray water in a circle pattern.

Concealed Pendant Sprinkler Head

Concealed pendant sprinkler heads are recessed in a ceiling and are covered with a decorative cap. The cap will fall away about 20°F prior to activation of the sprinkler. Once the sprinkler reaches its rated activation temperature, the head will drop below the ceiling. The water pattern of concealed sprinkler heads is a circle.

Upright Sprinkler Head

Upright sprinkler heads project up into a space and have deflectors that spray the water downward. They are generally used in mechanical rooms or other inaccessible areas to provide better coverage between obstructions like beams or ducts. They also provide a circle spray pattern

Side Wall Sprinkler Head

Side wall sprinkler heads stand out from a wall and have a deflector that sprays water away from the wall in a half-circle spray pattern. A second deflector also sprays water back toward the wall so that the wall is protected. These are used when sprinklers cannot be located in the ceiling.

Why is there liquid in the glass bulb of the Sprinkler Head?

The amount of liquid in the glass bulb plays a critical role in the proper activation of the sprinkler head. The fluid in the glass bulb expands when exposed to heat. When the rated temperature is reached, the internal pressure from the expanding fluid is sufficient to shatter the glass bulb, allowing the sprinkler to activate and water to flow. Missing or an insufficient amount of fluid will prevent the buildup of pressure inside the bulb thus preventing the sprinkler from operating until the glass melts, which is well beyond the intended operating time.

How do Sprinkler Heads operate?

Each sprinkler head contains a valve that opens to release water when a heat-sensitive element reaches a pre-determined temperature. Usually this will be at least 68°C, however, sprinkler heads that operate between temperatures of 57–230°C are also available – see below table.

Once a sprinkler head has been activated it delivers water directly onto the fire, dousing the flames and reducing the spread of fire.

Where would you usually find Sprinkler Heads installed in a premises?

Sprinkler heads are located at ceiling height (or in racks or on walls depending on the type of premises protected) – around one for every 9–15m² – and connected to a water supply.

Sources: Archtoolbox & BSA

If you would like further information, or would like to discuss the sprinkler system installed within your premises please do not hesitate to contact us