McDonnell & Miller 310488 Switch Assembly

The McDonnell & Miller 310488 is a field-replaceable SWA-42S Snap Switch Assembly engineered specifically for Series 42S low water cut-off and pump controllers. This single pole, single throw (SPST) mechanism provides precise automatic reset functionality, ensuring consistent boiler feed pump control and high-limit safety across residential, commercial, and industrial steam applications. Built with a robust housing and high-quality internal contacts, this switch assembly is designed to handle the cycling demands of medium pressure steam boilers up to 50 psi. As a critical HVAC replacement part, the 310488 maintains the integrity of the liquid level control system, preventing dry-fire conditions. Note that this snap-action switch is not interchangeable with older Series 42 mercury switches or Series 150S assemblies; it must be installed as a complete unit to ensure proper calibration and differential timing. Utilizing OEM McDonnell & Miller parts like the SWA-42S ensures seamless integration with existing housing and bellows assemblies for long-term system reliability.

• Direct OEM Compatibility: Specifically designed for 42S, 42S-A, and 42S-N models, ensuring a precise fit without field modifications.
• Snap-Action Precision: Features high-performance snap switches that eliminate "chatter" and provide clean electrical breaks.
• System Safety: Operates as a reliable low water cut-off component to protect boiler vessels from dangerous low-water conditions.
• Heavy-Duty Construction: Engineered to withstand the thermal and mechanical stresses inherent in steam boiler control environments.
• Automatic Reset: Facilitates seamless pump controller operation, returning the system to standard states once water levels are restored.

• Is the SWA-42S interchangeable with the Series 42 mercury switch? No, the 310488 switch assembly is designed exclusively for the 42S series and cannot be used to replace older mercury-style switch units.
• Can I replace individual components within the switch assembly? No, McDonnell & Miller requires that snap switches be replaced as a complete assembly to maintain safety listings and operational accuracy.
• What is the maximum pressure rating for this assembly? This switch assembly is rated for use in systems with a maximum operating pressure of 50 psi.

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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.