Potter WCS Series Water Column Switch is an electronic supervisory switch used to detect the presence of a conductive fluid (water) that can accumulate or become trapped in the piping directly above the clapper on a Dry-Pipe or Pre-Action valve. The electronic circuitry of the WCS is designed to indicate the presence of water accumulated to a specific elevation, that if left unattended could impair or prevent the operation of a dry pipe or pre-action automatic sprinkler valve. The yellow LED indicates the presence of water. The green LED indicates that the input voltage is present.