McDonnell & Miller 69 Cut Off

The McDonnell & Miller 153900 (Series 69) is a professional-grade mechanical low water cut-off designed for reliability in low-pressure steam boiler applications. This auto reset unit features a 4 1/8" insertion length and is engineered for mounting directly into 2 1/2" NPT boiler side tappings, making it compatible with residential and commercial boilers of any steaming capacity. By utilizing a packless bellows and a dual-switch assembly, this control ensures precise operation of the burner circuit and can simultaneously trigger an alarm or an electric water feeder. Built for durable performance in harsh boiler environments, the Model 69 maintains a 20 PSI max steam pressure rating. For contractors, the adjustable BX outlet simplifies field wiring and orientation. This float type LWCO is the industry standard for preventing dry-firing, protecting the heat exchanger from terminal damage when water levels dip below safe thresholds.

• Direct Boiler Mounting: Fits standard 2 1/2" NPT side tappings for a streamlined installation without complex piping.
• Dual Switch Logic: Features fixed-position dual precision switches for simultaneous burner cut-off and water feeder activation.
• Packless Bellows Design: Eliminates common leak points found in traditional shaft-seal designs for increased longevity in steam environments.
• Universal Capacity: Rated for low-pressure steam boilers of any steaming capacity up to its 20 PSI limit.
• Flexible Wiring: The adjustable BX outlet provides 360-degree rotation to accommodate tight clearances in the boiler room.

Common Questions:

What is the difference between auto-reset and manual-reset on the Series 69?
This specific 153900 model is an auto reset LWCO; it automatically restores power to the burner once the water level returns to a safe operating point. Manual reset versions require a technician to physically reset the device after a low-water event.

Can this be used on a hot water boiler?
The Series 69 is specifically engineered for steam boiler applications. For hot water (hydronic) systems, float-type or probe-type cut-offs rated for higher pressures and different mounting configurations are typically required.

What electrical loads do the switches handle?
The dual switches are designed to handle standard 120V or 240V burner circuits and are also compatible with 24V and self-generating millivolt systems, providing versatile integration for various control headers.

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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.