Description
Xylem-McDonnell & Miller FS254 General Purpose Liquid Flow Switch
The Xylem-McDonnell & Miller FS254 is a reliable, general-purpose liquid flow switch engineered for a wide range of hydronic and industrial fluid systems. Featuring a 1″ NPT connection and a single-pole, double-throw (SPDT) snap-action switch mechanism, the FS254 provides accurate, responsive flow detection to protect pumps, boilers, and other liquid-handling equipment from dry-run or no-flow conditions. The rugged NEMA 4 enclosure ensures dependable performance in demanding indoor and outdoor environments where moisture and dust are a concern.
Versatile Paddle Selection
The FS254 ships complete with four stainless steel paddle options — 1″, 2″, 3″, and 6″ — allowing the installer to match the paddle size to the pipe diameter and fluid velocity of the specific application. Stainless steel construction ensures corrosion resistance across a broad range of liquid media.
Key Features
- 1″ NPT pipe connection for straightforward installation into existing piping
- SPDT snap-action switch for reliable make/break switching in control circuits
- NEMA 4 rated enclosure — suitable for indoor and outdoor use, resistant to windblown dust and rain
- Includes four stainless steel paddles: 1″, 2″, 3″, and 6″ to accommodate various pipe sizes
- General-purpose design suitable for water, hydronic heating/cooling systems, and compatible liquid media
- Part Number: 120610
Typical Applications
- Hydronic heating and cooling systems — flow verification and pump protection
- Boiler system interlock circuits
- Chilled water and condenser water loops
- Industrial liquid process piping
- General HVAC water distribution systems
Why Choose McDonnell & Miller by Xylem
McDonnell & Miller, a brand of Xylem, has been a trusted name in flow and level controls for over a century. The FS series flow switches are widely specified by mechanical engineers and installed by HVAC professionals for their proven durability, ease of installation, and broad compatibility with commercial and industrial hydronic systems.







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