McDonnell & Miller FS7-4WL Snap Switch

The McDonnell & Miller FS7-4WL (Part Number 120301) is a heavy-duty, industrial-grade liquid flow switch engineered for high-demand applications requiring precise flow monitoring. Featuring a 1-1/4" NPT connection and a robust SPDT snap switch, this unit is designed for integration into control circuits that signal alarms, start motors, or cycle pumps. The FS7-4WL is built for durability with an extended paddle arm and trimmable stainless steel paddles, allowing for custom field adjustments to meet specific flow velocity requirements. Its NEMA 4X enclosure provides superior protection against corrosion and environmental ingress, making it suitable for both indoor and outdoor installations. Rated for a maximum pressure of 300 PSI and fluids up to 300°F (149°C), this industrial flow switch is a reliable solution for chilled water systems, heating loops, and process cooling where flow switch installation accuracy is critical to system protection.

Technical Specifications and Benefits

• High-Pressure Capability: Rated for a max pressure of 300 PSI, ensuring performance in demanding hydraulic systems.
• NEMA 4X Enclosure: Water-tight and dust-tight housing protects internal components from harsh environments.
• Customizable Flow Sensitivity: Includes trimmable stainless steel paddles for precise calibration based on pipe diameter and flow rate.
• Versatile SPDT Switching: Single pole, double throw action facilitates seamless integration into automation and safety interlocking systems.
• Durable Construction: Brass body and stainless steel internal components resist mineral buildup and mechanical wear.

Common Questions

Can the McDonnell & Miller FS7-4WL be used in both vertical and horizontal piping?
Yes, the FS7-4WL is designed for installation in both horizontal and vertical upward-flow piping. It should not be installed in downward-flow lines as gravity may affect the paddle return. Ensure a straight pipe run of at least 5 pipe diameters on both sides of the switch to minimize turbulence.

How do I adjust the sensitivity for low-flow applications?
Sensitivity is adjusted by trimming the stainless steel paddles to the appropriate length marked for your specific pipe size. For flow switch troubleshooting or fine-tuning, the internal adjustment screw can modify the switch actuation point to match your system’s minimum flow requirements.

Is this switch compatible with hazardous or corrosive fluids?
The FS7-4WL features a brass body and stainless steel paddles. While highly resistant to standard water and glycol solutions, always verify the industrial flow switch chemical compatibility with your specific fluid and temperature profile before installation.

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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.