McDonnell & Miller FS4-3RP-T Switch

The McDonnell & Miller FS4-3RP-T (Part #114639) is a standard-setting liquid flow switch engineered for heavy-duty service in commercial HVAC and hydronic systems. This paddle flow switch features a 1" NPT connection and is designed to provide reliable equipment protection in chilled water, boiler, and process applications. Equipped with high-sensitivity SPDT switch contacts, it seamlessly integrates into control circuits to cycle pumps, fire alarms, or trigger emergency safety shutdowns upon flow loss. The unit supports an operating pressure up to 160 PSI and includes a factory-integrated manual test button for rapid field validation without requiring system drainage. Built for durability, the assembly includes both 1" and 6" stainless steel paddles, ensuring precise flow switch installation across various pipe diameters. This modular design makes it an essential component for technicians requiring a versatile flow sensing solution that handles ambient temperatures up to 135°F and liquid temperatures up to 250°F.

• Universal Compatibility: Includes multiple stainless steel paddles to fit pipe sizes from 1" to 6" for maximum field flexibility.
• Enhanced Safety: Features a built-in test button for verifying switch operation and circuit integrity during routine maintenance.
• Robust Construction: Rated for a maximum pressure of 160 PSI and designed for long-term performance in demanding hydronic environments.
• Flexible Control: The SPDT flow switch configuration allows for simultaneous control of primary equipment and secondary alarm indicators.
• Industrial Standard: Features a 1" NPT connection for simplified flow switch installation in standard piping headers.

Can the FS4-3RP-T handle high-temperature boiler applications?
Yes, this switch is rated for liquid temperatures up to 250°F (121°C), making it suitable for both hot water boilers and chilled water loops.

How do I adjust the sensitivity for different flow rates?
The unit features an internal sensitivity adjustment screw that allows technicians to calibrate the flow or no-flow activation point based on specific system GPM requirements.

Is this switch suitable for use in hazardous or outdoor locations?
The standard FS4-3 model features a NEMA 1 enclosure designed for indoor use; for applications requiring a NEMA 4X rating, professional contractors should specify the water-tight version.

Disclaimer: While we strive for 100% accuracy, product data and specifications are subject to change. Please contact our team to confirm compatibility or technical details before purchasing.