Single-Interlocked Preaction Systems are commonly used where the sprinkler system piping and/or sprinkler may be subject to damage. The most common applications are in areas where it is important to control accidental water discharge due to a damaged sprinkler or damaged sprinkler piping. Viking’s supervised Single-Interlocked Preaction Systems use a Viking Deluge Valve and a pneumatically pressurized automatic sprinkler system.  The system piping is pneumatically pressurized for supervisory purposes only. This feature serves to prevent undetected leaks.  If the system piping or a sprinkler is damaged, supervisory pressure is reduced and a “low air” alarm is activated. Pneumatically controlled preaction systems require a pneumatic release system, equipped with thermostatic (rate of rise) releases, and/or fixed temperature releases, and/or pilot heads. Release trim for the pneumatically controlled deluge valve requires a pneumatic actuator normally held closed by pressure maintained in the pneumatic release system. In fire conditions, operation of the pneumatic release system opens the deluge valve to fill the system with water. If any sprinklers have opened, water will flow from the system. If sprinklers have not opened, water will be in the sprinkler system piping when the sprinkler operates. A sprinkler head must open before water flows from the system.