McDonnell & Miller FS4-3S General Purpose Liquid Flow Switch

FS4-3S General Purpose Liquid Flow Switch delivers reliable paddle-based flow sensing for nominal 1 inch piping. This universal paddle-type switch features a threaded end connection and SPDT snap switch for flexible control in pumping, boiler, and HVAC applications. Designed for easy installation and maintenance. Engineered for versatility, it supports a wide operating range from 32 to 300°F and up to 160 PSI, with clear flow specifications of 6–10.2 GPM (flow) or 3.6–9.2 GPM (no flow).

Built for durability, the FS4-3S uses a hardened stainless steel bearing and a sealed Monel bellows to resist wear in challenging liquids. Electrical ratings include 7.4 A at 120 VAC and 3.7 A at 240 VAC, with an input supply rating of 125 VA at 120/240 VAC (50/60 Hz). It is UL and CSA approved for North American use, ensuring reliable performance in demanding environments.

• Sensitivity adjustable screw for precise activation
• Dual electrical knock-outs for flexible wiring options
• Hardened stainless steel bearing for longevity
• Sealed Monel bellows to handle aggressive liquids