McDonnell & Miller FS5-3/4 Switch

The McDonnell & Miller FS5-3/4 Flow Switch (Part Number 114760) is a heavy-duty, in-line solution designed for contractors managing hydronic heating systems and commercial water lines. Built with a robust brass body and EPDM elastomer, this general purpose liquid flow switch provides high-reliability low flow rate sensitivity without the need for a secondary pipe tee. It features a single pole, double throw (SPDT) snap acting switch, allowing for seamless integration into pump control, alarm signaling, or burner cutout circuits. The 3/4" NPT connection and integrated sensitivity adjusting screw allow for precise field calibration to meet specific system GPM requirements. Rated for a maximum operating pressure of 150 psi and fluid temperatures up to 250°F, this unit is engineered to withstand demanding mechanical room environments while ensuring dry-run protection and consistent flow monitoring in closed-loop configurations.

• In-Line Design: Eliminates the labor and materials required for a pipe tee, simplifying installation in tight mechanical spaces.
• Precision Control: The SPDT snap switch provides reliable electrical make/break for motors, signal lights, and limit controllers.
• Field Adjustable: Features an external sensitivity screw to fine-tune flow switch actuation points based on specific application velocities.
• High Temperature Resilience: Reliable performance in high-temp hydronic loops with a 250°F maximum threshold.
• Corrosion Resistance: Brass construction and EPDM components ensure long-term durability in water-based heating and cooling systems.

What is the minimum flow rate required for actuation?
The McDonnell & Miller 114760 is designed for high sensitivity, typically actuating at approximately 1.5 GPM, though this can be adjusted using the sensitivity screw to fit the system's specific flow characteristics.

Can this flow switch be installed in vertical piping?
For optimal performance and accuracy of the liquid flow sensor, it is recommended to install the unit in a horizontal pipe run. Vertical installations may affect the gravity-return of the internal paddle mechanism.

Is the FS5-3/4 compatible with glycol or petroleum-based fluids?
This specific model (brass/EPDM) is engineered for water applications. For systems utilizing petroleum-based compounds, the stainless steel "S" series with Buna-N seals is required to ensure chemical compatibility.

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.