McDonnell & Miller 63 Low Water Cut Off

The McDonnell & Miller 63 Low Water Cut Off (Part Number 142400) is a heavy-duty, float-operated safety control designed for residential, commercial, and industrial boiler applications. This mechanical LWCO is specifically engineered for use with both hot water and steam boilers, providing a critical layer of protection against dry-fire conditions. Featuring a 1" NPT threaded connection for equalizing pipes, it is rated for a maximum boiler pressure of 50 PSI. This model includes a dual-switch assembly (No. 2 Switch), allowing for simultaneous low water cut-off and the activation of an electric water feeder or an external alarm. The automatic reset functionality ensures the burner circuit restores power once safe water levels are detected, though it must be installed in series with all other operating limits. For technicians working on high-input systems, this unit supports 120 VAC and 240 VAC electrical ratings and can be utilized with TC-4 valves for streamlined testing in hot water systems.

• Universal Application: Versatile design suitable for low pressure steam and hot water systems across various boiler capacities.
• Dual Switch Logic: Integrated No. 2 switch manages both the burner circuit and automatic water feeder or alarm signals independently.
• Robust Mechanical Build: Features a pack-less bellows and specialized float mechanism to withstand 50 PSI maximum pressure.
• Contractor-Friendly Install: Uses 1" FIP tappings for equalizing lines, facilitating standard HVAC piping configurations.
• Auto-Reset Efficiency: Minimizes downtime by automatically restoring the burner circuit after the boiler water level is corrected.

• Can this be used on a steam boiler? Yes, the Series 63 is rated for steam boiler applications with a maximum pressure of 50 PSI, though 20 PSI is the typical limit for low-pressure steam residential setups.
• What size are the equalizing port connections? This unit features 1" NPT (National Pipe Thread) connections for the equalizing lines.
• Does it require a blow-down valve? Yes, a blow-down valve is required in the lower equalizing line to clear sediment from the float chamber and test the cutoff operation.

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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.