System of discharge devices (sprinklers) distribution piping to supply water or other extinguishants to these devices, one or more sources of extinguishants under pressure, flow controlling devices (valves) and devices to actuate the system when a Fire occurs. The four basic types of systems are: Deluge : System in which all sprinkler heads are open and water (or other extinguishants) is held back by a main (deluge) valve. When this valve is opened by the actuating device, the extinguishant is delivered. and discharged from all heads simultaneously. A deluge system generally is used to wet down a large area quickly. Such as a sports arena. Dry-Pipe : System in which all piping contains only air under pressure. When a sprinkler head opens, the air pressure is released and the dry-pipe valve opens, permitting an extinguishant to enter the system and to flow out of any open sprinkler heads. A dry-pipe system is generally used where pipes may freeze. Pre-Action : System similar to a dry-pipe system except that air pressure may or may not be used to keep the system dry. The main control valve is opened by an actuating device, which permits the extinguishant to flow to the individual sprinkler heads and the system then functions as a wet pipe system. A pre-action system is generally used where piping is subject to mechanical damage and where it is important to prevent accidental discharge of extinguishant. Wet-Pipe : System in which all piping is filled with an extinguishant under pressure to be released by the fusible mechanism in the sprinkler head.SS : Steamship, steam powered ship (Steam driven turbines).