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Here is an excellent value on a UL-recognized flow sensing switch that can turn a heater, chiller, alarm, pump, etc., up to 2 hp (@ 230V) on or off. The ST9 is factory adjusted to close the circuit at 14 gpm and open it at 6 gpm but also field adjustable over a wider range. At 40 gpm, this flow switch causes only 6" of H2O pressure loss. A "flapper" (piston in ST12) moves with water flow, actuating a magnetic switch on the outside of the pipe. Water cannot reach the electrical section! Operates by sensing water flow only (unaffected by pressure).
Plumbing is PVC slip socket. ST11 and ST12 are recommended for booster pumps and feature a N.O./N.C. setting. Rated at 50 psi, 125VAC to 25 A (1 hp motor) or 250VAC to 25 A (2 hp motor). Switch is single pole single throw (one wire in, one wire out) with 1/2" FNPT conduit connections (ST9 has connections on both sides; ST11 and ST12 have connections on one). One plastic plug (shown in black) is included. Switches measure 6" x 6". One-year warranty. Made in USA.