McDonnell & Miller FS7-4W Snap Switch

The McDonnell & Miller FS7-4W (Part Number 120201) is a heavy-duty industrial liquid flow switch engineered for high-demand hydronic and process applications requiring a NEMA 4X enclosure. This unit features a 1 1/4" NPT connection and is designed with a brass body and sealed tube construction to isolate the SPDT snap switch from the process fluid. Rated for a maximum pressure of 300 PSI and fluid temperatures up to 300°F, it provides high-reliability liquid flow sensing in environments prone to moisture or dust. The magnetic switching mechanism eliminates the need for bellows, reducing fatigue-related failures common in standard switches. Contractors can utilize the trimmable stainless steel paddles to field-calibrate the device for pipes ranging from 1 1/4" to 16". An external sensitivity screw allows for precise flow rate adjustment without breaking the seal, ensuring the Series FS7-4W stays water-tight during commissioning.

• Environmental Protection: The NEMA 4X rated housing ensures durability in wash-down and corrosive industrial environments.
• Broad Pipe Compatibility: Includes trimmable stainless steel paddles suitable for large-diameter lines up to 16 inches.
• Magnetic Switching: Utilizes a magnetic link to actuate the SPDT snap switch, removing the physical stress point of a bellows.
• High-Pressure Tolerance: Robust brass construction supports system operating pressures up to 300 PSI.

What are the electrical ratings for this snap switch?
The single pole, double throw (SPDT) switch is rated for 7.4A at 120VAC and 3.7A at 240VAC full load, making it compatible with most industrial control circuits and pump starters.

Can the FS7-4W be installed in vertical piping?
This model is designed for horizontal pipe runs. If used in vertical piping with upward flow, the switch sensitivity must be adjusted to account for the weight of the paddle and gravity, which may affect the standard flow/no-flow set points.

Is this switch suitable for hazardous locations?
While the FS7-4W is water-tight (NEMA 4X), it is not an explosion-proof model. For Class I or Class II hazardous environments, the FS7-4E series is the specified industry standard.

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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.