McDonnell & Miller 63-HD Head Mechanism

The McDonnell & Miller 63-HD Head Mechanism (Part Number 142600) is a heavy-duty field replacement designed for Series 63 low water cut-offs. As a veteran-grade mechanical LWCO solution, this auto-reset head assembly provides essential protection for both hot water and steam boilers in residential and commercial environments. Engineered to manage boiler pressure up to 50 PSI, the 142600 integrates the No. 2 SPDT switch to ensure reliable burner circuit interruption or alarm activation during a low water condition. By replacing only the 63-HD head mechanism, contractors can restore system safety without disrupting existing piping, providing a cost-effective alternative to full unit overhauls. This mechanism is crucial for high-input systems where automatic reset capability is required to maintain continuous operation after water levels are corrected. This genuine McDonnell & Miller replacement part ensures precise liquid level control and serves as a primary or secondary safety limit in hydronic heating systems.

• Streamlined Installation: Designed for direct bolt-on replacement to the float chamber, eliminating the need to cut or re-thread 1-inch NPT equalizing lines.
• Robust Switching: Features the No. 2 Switch (110000) for standard SPDT functionality, handling up to 10.2A at 120VAC or 5.1A at 240VAC.
• Dual Application: Fully compatible with both steam boilers and hot water systems when used with appropriate check valves like the TC-4.
• Heavy-Duty Construction: Built to withstand the rapid cycling and chemical environments common in industrial boiler water level management.

• Is this compatible with the manual reset 63-M models? No, this is an auto-reset mechanism. For applications requiring a manual lockout, use the 143200 (63-M-HD) instead.
• Does this include the float assembly? This is the head mechanism only; it includes the mechanical assembly and switch but requires your existing float chamber for full operation.
• How often should the head mechanism be inspected? In standard commercial boiler applications, technicians should perform a blow-down and visual check annually, with a recommended replacement interval every 5 years for safety redundancy.

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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.