McDonnell & Miller 6667-MV Cut Off

The McDonnell & Miller 6667-MV (Part Number 153850) is a heavy-duty, float-operated replacement head mechanism specifically engineered for steam boiler applications. Designed for seamless integration into existing Series 67, 61, 69, and 767 low water cut-offs, this mechanism includes the specialized No. 11-MV millivolt switch. This configuration is essential for contractors servicing self-generating millivolt circuits or 24 VAC systems where a mechanical cut-off is required to maintain safety without relying on line voltage. The unit is rated for a 20 PSI max steam pressure, providing a rugged solution for low-pressure steam environments.

Replacing the head mechanism allows for a complete internal rebuild of the low water cut-off without the need to break down the primary boiler piping. This mechanical low water cut-off assembly features a high-grade bellows and float design, ensuring precise vertical movement to translate water level changes into switch action. By selecting the 6667-MV, you are ensuring that the pilot duty safety circuit will reliably interrupt the burner cycle if the water level drops below the safe operating line, protecting the heat exchanger from dry-firing and catastrophic failure.

• Millivolt Compatibility: Includes the 11-MV switch, perfect for maintaining or repairing off-grid and self-powered steam systems.
• Efficient Serviceability: Designed as a "drop-in" replacement head mechanism, meaning you can swap the internals while leaving the original cast iron body in place.
• High-Pressure Tolerance: Rated for systems up to 20 PSI, making it a versatile choice for residential and light commercial steam boilers.
• Durable Construction: Features a resilient bellows assembly that withstands the harsh thermal cycling of steam service.

Can the 6667-MV be used on a standard 120V system?
While the 11-MV switch is rated for millivolt service and 24 VAC, it is not recommended for high-amperage 120V burner circuits. For standard line voltage applications, the 6667 head with an 11-MD switch is required.

Does this include the gasket for installation?
Yes, the head mechanism typically includes the necessary mounting gasket for the flange. It is critical to clean the flange surface of the existing body thoroughly before installation to ensure a steam-tight seal.

Will this work if my boiler has an automatic water feeder?
Yes, the McDonnell & Miller 11-MV switch provides terminals for both the burner circuit and a secondary signal for an alarm or a low-voltage water feeder, allowing for synchronized control of water levels.

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.