the supervised system should record in inches of water rather than pounds per square inch. The second system is the unsupervised pre-action system. It has no means of continuous monitoring.
A combined system (fig. 8-12) is a special purpose arrangement using two modified dry pipe valves connected to tripping devices and piped in parallel to supply water to the same sprinkler system. The piping net work is filled with air under pressure. When a fire is detected, an exhauster at the end of the system opens and releases the air within the system. The system then operates the same as a pre-action system. However, if the detection system fails, the combined system acts the same as a dry pipe system and allows water to be admitted to the system when the sprinklers open, discharging the air from the piping network.
Figure 8-12. - Combined system header arrangement.
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.Continue Reading