TYPES OF SPRINKLERS
Sprinklers are nozzles placed at intervals along the piping network to distribute a uniform pattern of water on the area being protected. To attain maximum efficiency, the stream of water must be broken into droplets. A deflector (part of the frame of the sprinkler) breaks up the water.
You, as a UT, will generally install sprinklers to meet the specifications and plans of a project. When you require more information on proper locating of sprinklers, refer to the National Fire Protection Association Code Book Number 13 (NPFA #13), entitled Installation of Sprinkler Systems.
Automatic sprinklers are designed for specific applications based on orifice size, deflector design, frame finish, and temperature rating. Sprinklers have orifices ranging in size from 1/4-inch to 1/2-inch diameter graduated by 1/16-inch increments. There is also one 17/32-inch size orifice. Deflectors give different patterns of water distribution and allow the sprinkler to be placed in various locations such as upright, pendent, or sidewall (fig. 8-13). Next, sprinkler frames may
Figure 8-13.-Sprinkler deflector styles.
be plated for appearance or they maybe coated for protection from an adverse environment. For example, sprinklers that will be used in corrosive atmospheres are either lead-or wax-coated. Finally, automatic sprinklers are normally held closed by heat-sensitive elements that press down on a cap over the sprinkler orifice and are anchored by the frame of the sprinkler. The heat-sensitive elements melt and release at different temperatures depending on application. Sprinklers are color coded to identify the temperature range rating of the fusible element (table 8-1). Color coding is not required for plated sprinklers, ceiling sprinklers, or similar decorative types.
There are basically four types of release mechanisms for automatic sprinklers. They are the fusible link, frangible bulb, frangible pellet, and bimetallic element.
Figure 8-14.-Fusible link automatic sprinkler.
The fusible link sprinkler (fig. 8-14) is kept closed by a two-piece link held together by a solder with a predetermined melting point. When the solder melts, the levers pull the two-piece link apart and fly away from the sprinkler. Pressure in the piping network pushes the cap from the orifice of the sprinkler to discharge water.
The frangible bulb sprinkler (fig. 8-15) has a small bulb made of glass between the orifice cap and the sprinkler frame. The bulb is partially filled with a liquid. Air fills the remaining space. Heat from a fire will cause the liquid to expand against the air causing the glass bulb to shatter and opening the sprinkler for water discharge.
Figure 8-15.-Frangible bulb automatic sprinkler.
Table 8-1.-Sprinkler Temperature Ratings
A frangible pellet sprinkler (fig. 8-16) has a rod between the orifice cap and sprinkler frame. The rod is held in place by a pellet of solder under compression. When the solder melts, the rod moves out of the way of the orifice cap. The cap is pushed off by the water pressure in the piping network.
The bimetallic element sprinkler (fig. 8-17) uses a disk made of two distinct metals as a heatsensitive element. When the sprinkler is off, the disk maintains pressure on a piston assembly. When a fire occurs and the temperature reaches the sprinkler's rating, the disk flexes and opens, releasing pressure on the piston assembly and allowing a small amount of water to bleed out of the piston chamber faster than it can be replaced through a restrictor. The water pressure in the piping network pushes the piston down and allows water to discharge from the sprinkler. When the temperature of the heat-sensitive element is reduced, the element returns to its normal position and allows water to pass through the restrictor, filling up the piston chamber, forcing the piston into the closed position, and stopping water discharge. This sprinkler can be used to automatically cycle on and off as necessary; for example, to put out a rekindled fire.
Other sprinkler heads that do not have release mechanisms include the dry pendent sprinkler, the open sprinkler, and water spray nozzles.
Figure 8-17.-Bimetallic element automatic sprinkler.
Figure 8-16.-Frangible pellet automatic sprinkler.
A dry pendent sprinkler (fig. 8-18) is used when pendent sprinklers must be placed on dry pipe systems or in wet pipe systems when the area to be protected is subject to freezing (such as a walk-in reefer or outside shop area) and the piping network is installed in a heated area. This sprinkler is fitted with a tube within an attached pipe. The tube holds the water sealing elements in place against a watertight seal at the top of the pipe. When the sprinkler is actuated, the tube drops down and releases the elements through the tube and out the open sprinkler with the water discharge.
Open sprinklers consist only of a sprinkler frame and deflector. They are used on special sprinkler systems such as deluge or rapid reaction systems (fig. 8-19).
Water spray nozzles (fig. 8-20) are used for special application of water in various patterns (for example, wide or narrow angle, long throw or flat patterns). The different patterns may be achieved by either internal or external deflection of the water stream depending on the type of nozzle.
Figure 8-18.-Dry pendent automatic sprinkler.