The Model VSR-FEX is a vane-type water flow switch for use on wet sprinkler systems located in hazardous locations. The unit may also be used as a sectional waterflow detector on large systems. The unit contains two single poles, double throw, snap action switches, and an adjustable, instantly recycling pneumatic retard. The switches are actuated when a flow of 10 gal per minute (38 L per minute) or more occurs downstream of the device. The flow condition must exist for a period of time necessary to overcome the selected retard period.