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 sprinklers may be subject to damage. If the system piping or a sprinkler is damaged, supervisory pressure is reduced and a “low air” supervisory condition is activated.