McDonnell & Miller 343200 Bellows Assembly

The McDonnell & Miller 343200 Bellows Assembly (Model SA63-5) is the critical mechanical linkage used in Series 63 low water cut-offs. As a veteran-grade replacement component, this assembly mediates the movement between the internal float and the electrical switch, ensuring the heavy-duty performance required for commercial and industrial steam boiler safety. This genuine OEM replacement part includes the bellows, the CO-106 cam assembly, and the CO-11 bellows assembly gasket to ensure a pressure-tight seal during installation. Designed for high-performance hydronic systems, the SA63-5 is engineered to withstand the rapid cycles of float-type low water cut-off (LWCO) devices, maintaining calibration even under the thermal stress of high-pressure steam. When the water level drops, the bellows translates the float's position to trigger the burner circuit interruption, preventing catastrophic dry-fire conditions. For contractors, using this McDonnell & Miller bellows ensures backward compatibility with existing Series 63 units, providing a precise fit that eliminates the risks associated with non-standard generic components.

• Precise Mechanical Linkage: Converts float movement into switch actuation with minimal friction for reliable boiler control.
• Full Kit Inclusion: Shipped with the CO-11 gasket and CO-106 cam, facilitating a complete rebuild of the lower head mechanism.
• Industrial Durability: Specifically calibrated for the Series 63 float-type controls to handle high-temperature and varying pressure demands.
• Safety Integrity: Prevents dry-firing by ensuring the burners shut down immediately when water levels fall below the minimum safe line.

• Is this assembly compatible with the McDonnell & Miller 63-M or 63-B? Yes, the 343200 (SA63-5) is the standard bellows assembly for all Series 63 float-type low water cut-offs.
• Should I replace the gasket during every bellows teardown? Absolutely. Reusing old gaskets in steam boilers leads to pressure leaks; this assembly includes a new CO-11 gasket for that reason.
• How do I verify if my bellows has failed? If you observe steam leakage into the switch compartment or restricted float travel during a blowdown test, the bellows is likely compromised and requires replacement.

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.