McDonnell & Miller FS7-4S Snap Switch

The McDonnell & Miller FS7-4S is a heavy-duty industrial liquid flow switch engineered for high-pressure applications where standard brass units fall short. Featuring a rugged stainless steel body and 120160 part number, this 1-1/4" NPT flow switch is rated for a maximum pressure of 1000 psi and fluid temperatures up to 300°F. The single pole, double throw (SPDT) snap switch mechanism provides reliable liquid flow detection for large pipe systems, making it a staple for hydronic heating, process cooling, and HVAC pump control. Its magnetic switching mechanism eliminates the need for vulnerable bellows, reducing the risk of fatigue in high-cycle industrial environments. This model includes trimmable stainless steel paddles to match specific pipe diameters from 1-1/4" to 16", ensuring precise flow rate sensitivity. As a veteran-preferred paddle-style flow switch, the FS7-4S is designed for NEMA 1 enclosure applications and maximum velocities of 10 feet per second.

• High-Pressure Durability: The 316 stainless steel construction handles up to 1000 psi, making it suitable for demanding industrial water flow applications.
• Maintenance-Free Design: No bellows to fail; the magnetic linkage separates the electrical compartment from the process fluid.
• Field Versatility: Trimmable paddles allow for customization to multiple pipe sizes on-site, reducing inventory needs.
• Precise Control: Features an adjustable sensitivity screw to fine-tune the flow setpoint for pump protection and system monitoring.
• Reliable Switching: SPDT snap action allows for "make" or "break" circuit logic, ideal for signaling alarms or interlocks.

Is the FS7-4S compatible with corrosive fluids?
Yes, the stainless steel wetted parts provide superior resistance compared to brass, though compatibility should always be verified based on the specific chemical profile of your system.

Can this switch be mounted in any orientation?
No, for optimal performance, the FS7-4S must be mounted on the top of a horizontal pipe in the upright position. Vertical installation is not recommended as it affects the paddle’s gravity-return and sensitivity.

What is the maximum fluid velocity for this model?
This liquid flow switch is designed for systems with a maximum velocity of 10 feet per second. High-velocity turbulence can lead to paddle fatigue or premature switch wear.

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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.