McDonnell & Miller 67 Low Water Cut Off

The McDonnell & Miller 67 Low Water Cut Off (Part Number 149400) is a mechanical float-operated control engineered for reliable steam boiler protection in residential and commercial applications. Designed for a maximum pressure of 20 PSI, this auto reset unit features quick hook-up fittings for efficient installation directly into gauge glass tappings. The 3/4" NPT connection and large float chamber facilitate stable operation, while dual 120V precision switches provide dedicated control for the burner circuit and optional electric water feeders or alarms. An integrated lever-operated, full-port blow down valve allows for routine maintenance and sediment removal without system depressurization. For technicians replacing legacy boiler controls, the adjustable BX outlet ensures clean conduit runs. This mechanical LWCO accommodates boilers of any steaming capacity, providing critical dry-fire protection through a proven bellows assembly and No. 11 switch mechanism.

• Dual Precision Switches: Independently manages the burner shutdown and high-limit alarm or water feeder activation.
• Quick Hook-Up Fittings: Simplifies mounting to 1/2" NPT gauge glass tappings, reducing installation time for contractors.
• Blow Down Valve: Includes a factory-installed ball valve for regular testing and float chamber flushing.
• High Compatibility: Universal design fits steam boilers of any BTU capacity, utilizing a standard 3/4" NPT connection.

• How do I test if the float is operational? Perform a blow down while the burner is firing. The water level should drop, causing the float to trip the switch and immediately shut off the burner.
• Can this unit be used for hot water boilers? While primarily designed for steam service, the Series 67 remains a mechanical float control; however, probe-type LWCOs are often preferred for modern hot water applications.
• What power supply does the No. 11 switch require? The standard switch is rated for 120V or 240V AC, supporting 7.4A at 120V and 3.7A at 240V full load.

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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.