McDonnell & Miller 51-S-HD Water Feeder

The McDonnell & Miller 51-S-HD (Part Number 135800) is a heavy-duty head mechanism only replacement designed specifically for Series 51-S mechanical water feeders. Engineered for high-capacity systems up to 35,000 sq. ft., this unit is critical for maintaining precise water levels in low pressure steam and hot water boilers. Proportional feed action ensures a steady response to boiler demand, preventing the rapid cycling that stresses high-volume commercial systems. This head assembly features a proportional feed design and is rated for a maximum vessel pressure of 35 PSI and a maximum water supply pressure of 100 PSI. By replacing just the head mechanism, contractors can restore full boiler water level control functionality by simply unbolting the float chamber, avoiding the need to disrupt existing piping. This robust assembly is built to withstand demanding industrial environments where cold water feed regulation is essential for protecting the heat exchanger from dry-fire conditions.

• Universal Compatibility: Serves as a direct-fit replacement for all McDonnell & Miller 51-S series mechanical feeders.
• High-Capacity Performance: Rated for large-scale systems up to 35,000 sq. ft. of radiation.
• Streamlined Installation: Designed for "head-only" replacement to minimize downtime and labor costs during boiler maintenance.
• Precision Build: Features a 1-inch screwed connection and operates effectively with inlet water temperatures up to 120°F.
• Safety Rated: Maintains a 35 PSI max vessel pressure threshold, ideal for low-pressure domestic and commercial steam boilers.

Common Questions Regarding the 135800 Head Mechanism:

Does this unit include the float chamber?
No, the 51-S-HD is the head mechanism only. It includes the internal bellows, valve assembly, and float linkage, but is designed to be bolted onto your existing 51-S float chamber.

Can I use this on a hot water boiler or is it only for steam?
This mechanism is dual-purpose and is rated for both low pressure steam and hot water boiler applications, provided the vessel pressure does not exceed 35 PSI.

What is the primary cause of failure for these feeders?
Technicians frequently find that sediment or "mud" buildup in the chamber can restrict float movement. If cleaning the bellows and valve seat does not restore proportional feeding, a full replacement of the head mechanism is the standard professional solution.

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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.