McDonnell & Miller 343400 Float and Gasket

When you are performing an annual teardown on a McDonnell & Miller Series 63 low water cut-off, the 343400 Float and Gasket assembly (Model SA63-30) is a standard replacement for maintaining system integrity. This OEM kit includes the precision-engineered float, the CO-12 head gasket, and the necessary rod component to ensure accurate liquid level sensing in high-demand steam and hot water boiler applications. Designed for a maximum boiler pressure of 50 psi, this mechanical assembly provides the physical buoyant force required to actuate the switch mechanism during low-water conditions. Replacing the float and gasket together is critical to prevent "iffy" seals and vacuum leaks that can lead to nuisance shutdowns or, worse, dry-firing. The high-grade construction resists the common pitting and corrosion found in aggressive boiler water environments, ensuring the Series 63 LWCO delivers a reliable cut-off signal to the burner circuit.

Key Benefits for Contractors:

• Direct OEM Compatibility: Specifically engineered for McDonnell & Miller 63 Series units, ensuring precise alignment with the internal bellows and switch rocker.
• Complete Service Kit: Includes the SA63-30 float assembly and the CO-12 gasket to provide a secure, leak-proof seal during reassembly.
• Durable Construction: Built to withstand commercial boiler pressures up to 50 psi and the thermal cycling typical of steam systems.
• Reliable Level Sensing: Ensures the mechanical buoyant force is sufficient to overcome internal friction for consistent low water cut-off protection.

Common Questions:

How do I know if the float needs replacement versus just the switch?
If you perform a blow-down and the burner fails to cut off but the switch tests fine for continuity, inspect the float. A waterlogged or corroded float will lose buoyancy, failing to drop and trip the mechanism.

Does this kit include the head gasket?
Yes, the 343400 kit includes the CO-12 gasket, which is required whenever the head mechanism is pulled for inspection or replacement to prevent steam leaks.

What is the maximum pressure rating for this float?
The SA63-30 is rated for use in systems with a maximum boiler pressure of 50 psi (3.5 kg/cm²).

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.