McDonnell & Miller FS7-4SW Snap Switch

The McDonnell & Miller FS7-4SW is a heavy-duty, industrial liquid flow switch engineered for high-pressure applications requiring precise flow monitoring. Featuring a 1 1/4" NPT connection and a 316 stainless steel body, this unit is rated for line pressures up to 1000 PSI (70 kg/cm²). The integrated single pole double throw (SPDT) snap switch provides reliable signaling for starting or stopping motors, burners, or alarms based on flow velocity. For versatile field installation, it comes equipped with trimmable stainless steel paddles (1", 2", 3", and 6") to match specific pipe diameters. The NEMA 4X enclosure ensures the internal components are protected against corrosive environments and moisture, making it a standard choice for process cooling, hydronic systems, and water treatment plants. This liquid flow controller (Part 120191) handles a maximum liquid temperature of 300°F (149°C), maintaining calibration stability under demanding thermal cycles.

• Corrosion Resistance: 316 stainless steel construction prevents pitting and degradation in harsh chemical or high-salinity fluids.
• High Pressure Rating: Rated for 1000 PSI, far exceeding standard flow switches for use in industrial grade piping.
• Field Customization: Trimmable paddles allow for precise setpoint adjustment across various flow velocities.
• Environmental Protection: NEMA 4X rated housing is watertight and dust-tight for outdoor or wash-down locations.

Common Questions

What is the maximum pressure rating for the FS7-4SW?
This model is built with a stainless steel body and bellows, allowing it to operate safely in systems with a maximum working pressure of 1000 PSI.

Can the FS7-4SW handle corrosive liquids?
Yes, the wetted parts are 316 stainless steel, making it compatible with many industrial fluids that would damage standard brass components.

How do I adjust the sensitivity of the switch?
Sensitivity is managed via the internal sensitivity adjustment screw and by trimming the stainless steel paddle to the appropriate length for your specific pipe size and required flow rate.

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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.