Pre-action sprinkler system

Pre-action sprinkler system - this is a combination of a standard sprinkler system and an independent approved system of heat or smoke detectors installed in the same area as the sprinklers. Like dry pipe systems the pipes are filled with air but water is only let into the pipes when the detector operates. Pre-action systems... 

There are four basic types of sprinkler systems wet pipes, dry pipes, pre-action, and deluge. These are described in the following sections. 

The principal difference between a pre-action system and a standard dry pipe system is that in the pre-action system, the water supply valve is actuated independently of the opening of the sprinklers. The water supply valve is opened by the operation of an automatic fire detection system, which immediately allows water to enter the overhead piping. Then, when the fire generates enough heat to fuse the sprinkler head, water is immediately discharged on the fire as with a wet pipe system. This system reduces the inherent time lag of a dry pipe system, but can still be used in unheated areas. An example of a pre-action system is shown in Figure 7-26. 

The availability of pre-action systems depends heavily upon the availability of the associated independent detection system. To compensate for this, systems should be designed so that the valve can be opened manually, both locally and at a constantly attended location. In addition, because of the complex mechanical valve arrangement, pre-action systems are less reliable than wet and dry pipe sprinkler systems. 

Annually Sprinklers free from corrosion, paint, and obstructions pipe free from corrosion control valves lubricated, closed and opened trip test on dry-pipe, pre-action, and deluge systems... 

Pre-action System A type of automatic sprinkler system in which thennostatic devices are employed to charge the system with water before individual sprinkler heads are fused. 

A variation of the dry-pipe system is the deluge system. The sprinkler heads are continuously open and water is prevented from entering the system by a deluge valve. When a fire is detected the valve to the water supply opens and water flows into the system and out of aU the sprinkler heads. This not only wets the immediate area of a small fire, but the entire area to which the fire may spread. This type of system is usually chosen when the contents of the space are unusually hazardous. A variation on this system is the pre-action system in which the sprinkler heads are not open, but when a fire is detected the deluge valve opens and water is supplied to the sprinkler heads. The water entering the system causes an alarm to be sounded. When the heat causes the sprinkler heads to fuse, or open, water is discharged onto the fire. 

Four types of sprinkler systems are available wet-pipe, dry-pipe, alternate and pre-action. A wet-pipe system can only be used in premises not subject to frost or ambient temperatures above 70 C. A dry-pipe system is only suitable in premises subject to continuous temperatures below 0 C or above 70 C. An alternate system which enables either wet or dry operation to be selected is suitable in premises subject to freezing during cold weather. Finally a pre-action system, which is a system with a separate heat or smoke detector that allows water into the sprinkler pipework before the first head operates, should only be used where none of the others is suitable. 

The pre-action system. This is similar to the deluge system, except that the sprinkler heads are kept sealed for some time before the water comes through. This delay enables firefighters to put out the fire before it is covered by water. 

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