Viking supervised VXD Single-Interlocked Preaction Systems utilize a Viking Model VXD Deluge Valve and a pneumatically pressurized automatic sprinkler system. This feature helps prevent undetected leaks. Single-Interlocked Preaction Systems are commonly used where the sprinkler system piping and/or sprinkler may be subject to damage. If the system piping or a sprinkler is damaged, supervisory pressure is reduced and a “low air” supervisory is activated. The electrically controlled preaction systems include an electric solenoid valve controlled by an approved release control panel (sold separately) with compatible detection system (sold separately). In fire conditions, when the detection system operates, the system release control panel energizes the solenoid valve open, causing the deluge valve to open. The sprinkler system fills 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 must open before water flows from the system.