McDonnell & Miller 64 Low Water Cut Off

The McDonnell & Miller 64 (Part Number 143600) is a heavy-duty mechanical low water cut-off engineered for reliable water level regulation in residential and commercial hot water and steam boilers. Designed for systems with a maximum boiler pressure of 50 PSI, this auto reset control features a 1" NPT threaded connection for seamless integration into equalizing piping. It utilizes a packless bellows construction and double-pole, single-throw (DPST) dual precision switches to independently manage burner circuits and alarm systems or electric water feeders. Rated for 120V or 240V applications, the float-operated Series 64 is a standard for contractors requiring a dependable safety interface that prevents dry-fire conditions. Its adjustable BX outlet simplifies field wiring, while the mechanical design ensures consistent actuation even in high-demand hydronic environments. Whether used as a primary or secondary safety limit, this low water cut-off provides the essential circuit interruption needed to protect boiler vessels and maintain system integrity.

• Universal Application: Suitable for both steam and hot water systems of any steaming capacity up to 50 PSI.
• Enhanced Durability: Features a packless bellows seal to eliminate common leakage points found in traditional shaft seals.
• Simplified Installation: The adjustable BX outlet and 1" NPT connections allow for flexible positioning during retrofits or new builds.
• Dual Switch Logic: Integrated dual precision switches allow for simultaneous burner cutoff and auxiliary alarm or feeder activation.
• Reliable Auto-Reset: Automatically restores the circuit once safe water levels are reached, reducing unnecessary service calls for manual resets.

• What size equalizing lines are required? This model requires 1" NPT equalizing piping to ensure proper float chamber response and buoyancy.
• How often should the float chamber be maintained? For systems under 15 PSI, blow down the float chamber weekly. For high-pressure steam applications, daily blow-downs are recommended to prevent sediment buildup.
• Can this be converted to a manual reset? Yes, the McDonnell & Miller 64 can be field-converted using a manual reset switch assembly (such as the 11M) if local codes require manual intervention after a low-water event.

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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.