The Model SD-WFD is a vane type water flow switch for use on wet sprinkler system s. The water flow contains two single pole, double throw, snap action switches and an adjustable, instantly recycling pneumatic retard. Vane-type water flow detectors shall be installed on system piping as designated on the drawing and/or as specified herein. Detectors shall have sensitivity in the range of 4 to 10 gallons per minute and a static pressure rating of 450 psi for 2˝–8˝ pipes. The flow condition must exist for a period of time necessary to overcome the selected retard period that is field adjustable. The delay mechanism shall be a sealed mechanical pneumatic unit with visual indication of actuation. The actuation mechanism shall include a polyethylene vane inserted through a hole in the pipe and connected by a mechanical linkage to the delay mechanism. Outputs shall consist of dual SPDT switches. Two conduit entrances for standard fittings of commonly used electrical conduit shall be provided on the detectors.