McDonnell & Miller 67-G Low Water Cut Off

The McDonnell & Miller 67-G is a float-operated mechanical low water cut-off engineered specifically for steam boilers and millivolt service applications. For contractors managing residential or commercial steam systems, this auto reset control provides critical burner protection by interrupting the millivolt burner circuit if the water level drops to a dangerous point. The unit features dual precision switches, allowing for simultaneous low water cut-off and the operation of an electric water feeder or alarm. With a maximum steam pressure rating of 20 PSI and a large float chamber to minimize the effect of surging water, the 149600 model ensures reliable performance in diverse steaming environments.

Designed for streamlined field installation, the McDonnell & Miller 149600 includes quick hook-up fittings for direct mounting into 1/2" NPT gauge glass tappings. The integrated lever-operated, full port ball valve facilitates mandatory blow-down procedures to clear sediment and verify float movement. An adjustable BX outlet further simplifies wiring for the HVAC technician. By maintaining the correct steam boiler water level, the 67-G prevents dry firing and protects the heat exchanger from terminal damage. This mechanical LWCO is a standard choice for 3/4" NPT connections where a dependable, non-electronic safety limit is required.

• Automatic Reset Functionality: Restores burner operation immediately once the boiler water level returns to a safe operating range.
• Millivolt Circuit Compatibility: Specifically designed for self-generating millivolt systems often found in older or specialized steam boilers.
• Dual Switch Versatility: Independent terminals support both the burner safety circuit and an electric water feeder or remote alarm.
• Simplified Blow-Down: High-capacity ball type blow-down valve ensures easy maintenance and proactive system flushing.
• Durable Construction: Heavy-duty float and bellows assembly engineered to withstand the rigors of low pressure steam environments.

How often should the 67-G blow-down valve be operated?
Technicians should perform a blow-down weekly during the heating season to ensure the float remains free of sediment and the low water cut-off switch triggers correctly.

Can this unit be used on a process steam boiler?
Yes, provided the system does not exceed the 20 PSI maximum pressure limit. It is suitable for any steaming capacity within that pressure range.

What is the connection size for the gauge glass?
The unit is equipped with quick hook-up fittings designed to install directly into the 1/2" NPT tappings typically used for a boiler’s water sight glass.

Does the 67-G require an external power source?
No, this specific mechanical LWCO is designed for millivolt service, utilizing the low voltage generated by the pilot assembly to complete the safety circuit.

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.