Description
The Xylem-McDonnell & Miller FS8-WJ is a general purpose liquid flow switch engineered for reliable flow detection in a wide range of hydronic and liquid piping systems. Featuring a 1″ BSPT connection and a Single-Pole Double-Throw (SPDT) snap-action switch mechanism, this unit delivers precise, dependable switching performance across demanding commercial and industrial applications.
Key Features
- 1″ BSPT threaded connection for straightforward installation into standard piping systems
- SPDT snap-action switch for reliable make/break switching on flow presence or absence
- Rated for liquid system pressures up to 160 PSI maximum
- Includes four interchangeable stainless steel paddle sizes: 1″, 2″, 3″, and 6″ — accommodating a broad range of pipe diameters
- Stainless steel paddle construction for corrosion resistance and long service life
- General purpose design suitable for water, hydronic heating/cooling systems, and compatible liquid applications
- Part Number: 120602
Paddle Selection Guide
The FS8-WJ ships with four stainless steel paddle options, allowing the installer to select the appropriate paddle length for the pipe size in use. Larger paddles are used in larger-diameter pipes to ensure proper actuation at the desired flow rate.
- 1″ paddle — for smaller pipe diameters
- 2″ paddle — for medium pipe diameters
- 3″ paddle — for larger pipe diameters
- 6″ paddle — for large-diameter or low-flow applications
Typical Applications
- Hydronic heating and cooling systems
- Boiler and chiller flow proving
- Pump protection and flow verification
- General liquid flow detection in commercial and industrial piping
Product Specifications
- Brand: Xylem-McDonnell & Miller
- Model: FS8-WJ
- Part Number: 120602
- Connection: 1″ BSPT
- Switch Type: SPDT Snap Switch
- Maximum Pressure: 160 PSI
- Paddle Material: Stainless Steel
- Included Paddle Sizes: 1″, 2″, 3″, 6″









