The Model VSR-ST is a vane type waterfl ow switch for use on wet sprinkler systems that use 1", 1-1/4", 1-1/2" or 2" pipe sizes. It is equipped with a union to accommodate installation in confi ned spaces. The unit contains two single pole double throw snap action switches and an adjustable, instantly recycling pneumatic retard. The switches are actuated when a fl ow of 10 gallons per minute (38 liters per minute) or more occurs downstream of the device. The fl ow condition must exist for a period of time necessary to overcome the selected retard period.