McDonnell & Miller FS4-3 NEMA 1 Flow Switch 1" SPDT with 6" Paddle

The McDonnell & Miller FS4-3 is a NEMA 1 rated general purpose liquid flow switch designed for reliable monitoring of fluid flow in commercial and industrial applications. This flow switch features a single-pole double-throw (SPDT) contact configuration for versatile control applications.

Key Features:

• NEMA 1 rated enclosure for indoor general purpose applications
• SPDT contact configuration for flexible control circuits
• 1-inch NPT connection size for standard pipe installations
• Includes 6-inch paddle (part number 123) for effective flow detection
• Actuates when liquid flow reaches sufficient velocity to move paddle
• De-energizes when flow stops or drops below set point
• Suitable for water, oils, and other compatible liquids

This flow switch is commonly used in HVAC systems, boiler applications, cooling towers, and process control systems where reliable flow detection is essential. The paddle-type design provides proven, mechanical flow sensing without requiring external power for the sensing element.