McDonnell & Miller 63-B Low Water Cut Off

The McDonnell & Miller 63-B (Part Number 142700) is a heavy-duty, float-operated mechanical low water cut-off engineered for reliable performance in residential and commercial hot water and steam boilers. As a veteran-grade boiler safety control, this unit features an automatic reset and a 1" NPT threaded connection, rated for a maximum pressure of 50 PSI. The integrated float block design ensures stable operation by reducing float movement caused by surging water levels, while the standard No. 2 switch provides a dependable electrical interface for burner circuit interruption. This float-type LWCO is a direct replacement for the 142700 and serves as a critical fail-safe to prevent dry-fire conditions. For hot water systems, it is best practice to utilize this control in conjunction with a TC-4 Test-N-Check valve to facilitate simplified testing and maintenance without needing to drain the entire system.

• Universal Application: Rated for both steam and hot water systems up to 50 PSI, making it a versatile choice for various boiler water level control configurations.
• Float Block Technology: The specialized housing minimizes turbulence within the chamber, ensuring precise float-operated cut-off cycles even in high-demand environments.
• Professional Grade Construction: Built with a packless bellows and dual precision switches for long-term durability in commercial HVACR applications.
• Easy Retrofit: The 1" NPT tapping allows for straightforward integration into existing equalizing lines, maintaining compatibility with standard McDonnell & Miller 63-B installations.

Common Questions

Is the 63-B compatible with both low-pressure steam and hot water boilers?
Yes, the 63-B is a versatile low water cut-off for boilers and is rated for both applications, provided the system pressure does not exceed 50 PSI.

How often should the McDonnell & Miller 142700 be tested?
Technicians should perform a blow-down test weekly during the heating season to clear sediment from the float chamber and verify that the burner circuit interrupts as the water level drops.

Can I use this as a secondary safety limit?
Absolutely. While often used as a primary control, it is frequently installed as a redundant mechanical LWCO on larger systems to meet modern safety codes and provide an additional layer of protection.

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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.