McDonnell & Miller 310802 Snap Switch

Optimizing liquid flow control in hydronic and industrial systems requires reliable electrical feedback, and the McDonnell & Miller 310802 Snap Switch is the standard for maintaining seasonal uptime. Specifically engineered as the direct replacement snap switch assembly for FS250 series flow switches (Model SW-FS250), this component ensures precise SPDT (Single Pole Double Throw) actuation. For contractors managing boiler flow switch maintenance, this assembly provides the sensitivity needed to prove flow before firing burners or starting chillers, protecting expensive heat exchangers from low-flow conditions.

The McDonnell & Miller 310802 is cross-compatible with the Series FS254 and is often used to field-repair general-purpose liquid flow switches. Built with a high-integrity snap-action mechanism, it eliminates the "hunting" often seen in worn-out assemblies, providing a crisp make-or-break signal. As a veteran-grade HVAC replacement part, it is designed for rapid installation into the existing housing, allowing you to restore system logic without a full valve body replacement. Its robust construction handles the high-cycle demands of commercial pumps and industrial cooling loops.

• Universal FS250 Compatibility: Designed specifically for the Series FS250 and FS254, ensuring exact mechanical alignment and electrical terminal positioning.
• SPDT Logic: Provides versatile wiring options for normally open or normally closed circuits, essential for interlocking pumps and safety controls.
• High-Cycle Durability: The snap-action design minimizes arcing and contact wear, extending the service life of the flow control system.
• Contractor-Focused Design: Facilitates quick field repairs to minimize system downtime during critical heating or cooling seasons.

Can the SW-FS250 replace switches in other McDonnell & Miller series?
While the 310802 is the dedicated assembly for the FS250 and FS254, always verify the internal mounting bracket. It is specifically calibrated for the cam-actuation found in these general-purpose liquid flow switches and is not a universal substitute for mercury-style or low-water cutoff switches like the 150S series.

What are the electrical ratings for this snap switch?
This switch typically supports standard pilot duty and motor loads up to 1/3 HP at 120/240 VAC. Always verify the specific FLA and LRA requirements of your interlocking relay or starter to ensure the switch remains within its operating parameters.

How do I verify if the snap switch needs replacement?
If the flow switch paddle is moving but the electrical circuit fails to "prove," or if you observe erratic continuity during bench testing, the internal snap mechanism has likely reached its cycle limit. Replacing the 310802 assembly restores the precision of the trip point.

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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.