Xylem-McDonnell & Miller FS1-J 1/2″ BSPT In-Line Liquid Flow Switch, SPDT

Description

Xylem-McDonnell & Miller FS1-J In-Line Liquid Flow Switch

The Xylem-McDonnell & Miller FS1-J is a high-sensitivity, in-line liquid flow switch engineered for dependable flow detection in hydronic heating, cooling, and fluid handling systems. Featuring a 1/2″ BSPT connection and a snap-acting SPDT (Single-Pole, Double-Throw) switching mechanism, the FS1-J delivers fast, precise response to changes in liquid flow — making it an essential safety and control device for a wide range of commercial and residential HVAC applications.

Key Features

• High-sensitivity paddle design detects low flow rates with accuracy
• Snap-acting SPDT switch provides reliable make/break switching action
• 1/2″ BSPT in-line pipe connection for straightforward installation
• Compact, in-line body design minimizes installation space requirements
• Suitable for use in hydronic heating and cooling systems, chilled water loops, and fluid process piping
• Durable construction for long service life in demanding HVAC environments
• Part Number: 113550

Typical Applications

• Hydronic boiler and chiller flow protection
• Pump proving and flow verification circuits
• Chilled water and hot water distribution systems
• Liquid cooling equipment protection
• Industrial fluid handling and process control

Why Choose the FS1-J?

McDonnell & Miller, a trusted Xylem brand, has been a leader in flow and level control for over a century. The FS1-J continues that legacy with a robust, field-proven design that protects equipment from dry-run or low-flow conditions. Its snap-acting SPDT output integrates easily with standard control panels, relays, and building automation systems, providing both safety shutdown and status monitoring capabilities.