McDonnell & Miller FS4-3S Switch

1" NPT, SPDT Switch, General Purpose Liquid Flow Switch with Stainless Steel Body for up to 160 PSI Max Pressure with 1", 2", 3", and 6" Stainless Steel Paddles (Part Number 114641)

FS4-3S is the direct replacement for FS4-3S-E

McDonnell & Miller FS4-3S Flow Switch – 1" NPT General Purpose Liquid Flow Switch with Stainless Steel Paddles

The McDonnell & Miller FS4-3S is a reliable and versatile general purpose liquid flow switch designed for monitoring flow rates in various industrial and HVAC applications. Featuring a robust stainless steel body and multiple paddle sizes, this 1" NPT SPDT switch supports a maximum pressure of up to 160 PSI, making it ideal for controlling electrically operated equipment such as signal lights, alarms, motors, automatic burners, and metering devices.

Key Features:

• Universal design compatible with a wide range of applications

• 1" NPT threaded connection for easy installation

• Single Pole Double Throw (SPDT) snap switch for precise control

• Hardened stainless steel bearings to reduce friction and extend switch life

• Sealed Monel bellows for enhanced durability and corrosion resistance

• Includes four stainless steel paddles: 1", 2", 3", and 6" (25mm, 50mm, 80mm, 150mm) for flexible flow detection

• Two electrical knockouts allow wiring connection from either end

• Sensitivity adjusting screw for easy flow rate calibration

• Replacement compatible with popular flow switch brands including Johnson/Penn, Potter/Taco, Watts, Hydro-level, and others

Specifications:

• Maximum Pressure: 160 PSI

• Connection Size: 1" NPT

• Paddle Material: Stainless Steel

• Electrical Configuration: SPDT (Single Pole Double Throw)

Applications:
Ideal for HVAC systems, boilers, pumps, and industrial fluid flow monitoring. The FS4-3S helps protect equipment by starting or stopping electrical devices based on liquid flow presence, ensuring efficient and safe operation.