McDonnell & Miller 347900 Assembly and Gaskets

The McDonnell & Miller 347900, also identified by model number SA150-106R, is a critical bellows assembly and gasket replacement engineered for Series 150 and 157 low water cut-off (LWCO) and pump controllers. For technicians servicing steam boilers, this assembly is the primary pressure-sensing component that translates water level changes into mechanical action for the switch head. Constructed with a corrosion-resistant Monel bellows, the unit is designed to withstand the high-temperature and high-pressure environments typical of industrial boiler applications up to 150 psi. When a boiler water level control fails to activate the pump or burner circuit, a ruptured bellows is often the culprit. Replacing the SA150-106R bellows restores the mechanical seal between the float chamber and the switch housing, preventing hazardous steam leaks into the electrical components. This OEM replacement part includes the necessary gaskets to ensure a pressure-tight seal during reinstallation on 42, 150, and 157 series models.

• Corrosion-Resistant Monel Construction: Engineered to handle aggressive steam environments and prevent premature fatigue or failure.
• Direct OEM Compatibility: Specifically calibrated for McDonnell & Miller 150 Series and 157 Series controllers, ensuring accurate logic for pump and burner circuits.
• Complete Sealing Kit: Includes high-grade gaskets to maintain a 150 psi operating pressure rating and prevent steam bypass.
• Restores System Safety: Facilitates proper low water cut-off functionality to protect the boiler from dry-firing conditions.

How do I know if my McDonnell & Miller bellows assembly needs replacement?
If you observe steam leaking from the switch housing or if the pump controller fails to respond to float movement despite a clear chamber, the bellows has likely lost its integrity and requires immediate replacement with the SA150-106R.

Is the SA150-106R compatible with older mercury switch models?
Yes, this bellows assembly is designed to work with both older mercury switch versions and modern snap-action switch assemblies found in Series 150S and 157S units.

Does this kit include the mounting screws?
Standard 347900 kits include the bellows and gaskets; however, it is standard practice for technicians to inspect the Torx or Allen head screws during teardown and replace them if corrosion is present to ensure proper torque specs.

This item is not eligible for free shipping.

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.