Pre-action systems are similar to wet-pipe systems only that water is not stored in the overhead piping preventing an accidental system discharge. Pre-action sprinkler systems prevent accidental activation by protecting fire hazards from unnecessary contact with water. The sprinklers in this type of system will only emit water if the fire cannot be extinguished by other means. This helps to prevent unnecessary or accidental water discharge, protecting valuable artifacts or expensive technology.
They require a large design space, and are ideal for areas with valuable contents including but not limited to museums, libraries, archives, refrigerated spaces and more. Pre-action systems are a combination of dry, wet and deluge systems that can be divided into single interlock and double interlock systems, depending on your building’s specific need.
Single Interlock System
Single interlock pre-action sprinkler systems bear resemblance to dry systems, but also contain a heat or smoke detector that must be activated before water enters the pipes. Similar to the process in a deluge system, a single interlock system utilizes a deluge valve and a supervisory air pressure system. Loss of air in the pipes will only operate an alarm and water will not be released from the pipes until an electric or pneumatic detection is activated.
Double Interlock System
Double interlock systems utilize automatic sprinklers and a pressure switch or pressurized piping that contains monitored, pressurized air or nitrogen. When the air pressure changes or disappears, the piping activates a trouble alarm. In addition to the alarm, a smoke / heat detection system are used to provide an alarm to the central control panel to signal the valve to “
open” the water line. Like single interlock systems, a heat or smoke detector must be activated before water enters the pipes. In a double interlock system, however, a sprinkler must also be activated before water flows through the pipes. If either fire detectors or sprinklers are activated by themselves, alone, water will not be released.
Application of Pre-Action Systems:
- Flammable Liquid Handling
- Aircraft Hangars
- High-Hazard Installations that use water based systems
- Refrigerated Spaces