McDonnell & Miller 51-2 Feeder

The McDonnell & Miller 51-2 (Part Number 135000) is a heavy-duty mechanical water feeder and low water cut-off (LWCO) designed for industrial and commercial low pressure steam and hot water boilers. Engineered for systems with a capacity exceeding 5,000 sq. ft., this unit provides critical protection by maintaining a consistent minimum safe water level regardless of electrical status. It features 1" NPT female connections and a snap-acting SPDT switch (No. 2 switch) specifically calibrated for low water cut-off and alarm actuation. This float-operated control supports a maximum vessel pressure of 35 PSI and an inlet water pressure of up to 150 PSI. The inclusion of a quick-change replaceable cartridge valve and integrated strainer streamlines field maintenance, ensuring reliable proportional feed action and sediment protection in high-demand hydronic or steam applications.

• Dual Functionality: Combines reliable mechanical water feeding with an integrated low water cut-off switch for comprehensive boiler safety.
• High-Capacity Performance: Optimized for large-scale boilers over 5,000 sq. ft. using cold water feed.
• Simplified Service: Features a quick-change cartridge valve and removable strainer for rapid onsite cleaning and replacement.
• High Pressure Tolerance: Handles up to 150 PSI water supply pressure and 35 PSI vessel pressure for versatile system integration.
• Non-Electrical Feeding: The mechanical feeder operates independently of electrical power, ensuring water levels are maintained during outages.

What is the difference between the Model 51 and the 51-2?
The standard Model 51 acts exclusively as a mechanical water feeder. The McDonnell & Miller 51-2 includes the factory-installed No. 2 SPDT switch, adding the essential low water cut-off safety function to shut down the burner during a low water event.

Can this unit be used for hot water heating boilers?
Yes, while commonly used in low pressure steam applications, the 51-2 is fully compatible with hot water boilers larger than 5,000 sq. ft. capacity provided the vessel pressure does not exceed 35 PSI.

How do I service the valve without replacing the whole unit?
The 135000 is designed for longevity; you can swap the valve assembly using the SA51-6 cartridge. This allows technicians to restore proportional feed accuracy without disturbing the primary piping or float chamber.

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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.