McDonnell & Miller 61 Low Water Cut Off

The McDonnell & Miller 61 Low Water Cut-Off (Part Number 140100) is a heavy-duty mechanical control designed for residential steam boiler applications. Engineered for systems with a 20 PSI maximum steam pressure, this float-operated safety device prevents catastrophic boiler failure by interrupting the electrical circuit if the water level drops below the safe operating line. The unit features 1" NPT connections for a secure fit into the water column and is equipped with a manual reset mechanism, ensuring a technician inspects the system before resuming operation. Its rugged construction provides reliable low water protection in gravity-return systems, maintaining the liquid level through a precision-engineered bellows seal that prevents steam from entering the switch housing. For contractors performing a steam boiler LWCO replacement, the 61 series remains the industry standard for durability and straightforward mechanical cut-off performance without the complexity of electronic sensors.

Key Benefits

• Proven Mechanical Reliability: Utilizes a float-and-bellows design that operates independently of water conductivity or probe fouling.
• Enhanced System Safety: The integrated Type A switch provides a positive break in the burner circuit until the water level returns to a safe state.
• Standardized Fitment: Features 1" NPT tappings, making it a direct-fit solution for most legacy and modern low-pressure steam systems.
• Durable Construction: Built to withstand the harsh environment of a boiler room, ensuring long-term boiler safety control.

Common Questions

What is the maximum pressure rating for the McDonnell & Miller 61?
This unit is strictly rated for low-pressure applications with a 20 PSI max steam pressure. Exceeding this limit can compromise the bellows and float mechanism.

Does this unit require a manual reset?
Yes, the 61 model requires manual intervention to reset the burner circuit once a low-water condition has occurred, facilitating safer diagnostic practices.

Can this be used on water boilers?
The No. 61 is specifically designed for steam boiler applications; for hot water heating systems, a probe-style or different mechanical LWCO should be selected based on the system's specific requirements.

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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.