Description
Xylem-McDonnell & Miller 51-B-2M Mechanical Water Feeder and Low Water Cut Off
The McDonnell & Miller 51-B-2M (Part Number 135500) is a combination mechanical water feeder and low water cut off designed for reliable protection and automatic water management on low pressure steam and hot water boilers. Built by Xylem’s trusted McDonnell & Miller brand, this unit integrates two critical boiler safety functions into a single, rugged assembly — helping to maintain proper water levels while guarding against dangerous low-water conditions.
Key Features
- Combination mechanical water feeder and low water cut off in one unit
- Designed for low pressure steam and hot water boiler applications
- 35 PSI maximum vessel pressure rating
- 1″ NPT connections for straightforward installation and compatibility with standard piping
- Snap-acting manual reset SPDT switch for positive, reliable switching action
- Float block design for accurate and dependable water level sensing
- Part Number: 135500
How It Works
The 51-B-2M uses a float block mechanism to continuously monitor boiler water levels. When the water level drops below the safe operating threshold, the snap-acting SPDT switch activates to cut off the burner, preventing dry-fire damage. Simultaneously, the mechanical water feeder automatically introduces fresh make-up water to restore the proper operating level. The manual reset feature ensures that an operator must consciously reset the control before the boiler resumes operation, adding an important layer of safety accountability.
Specifications
- Model: 51-B-2M
- Part Number: 135500
- Application: Low pressure steam and hot water boilers
- Maximum Vessel Pressure: 35 PSI
- Connection Size: 1″ NPT
- Switch Type: Snap-acting, manual reset SPDT
- Sensing Method: Float block
- Brand: Xylem-McDonnell & Miller
Why Choose the McDonnell & Miller 51-B-2M
McDonnell & Miller has been a trusted name in boiler protection controls for over a century. The 51-B-2M delivers the dual functionality of water feeding and low water cut off in a compact, proven design — reducing installation complexity and ensuring your boiler operates safely and efficiently. The manual reset SPDT switch provides peace of mind by requiring deliberate operator intervention after a low-water event, making this an ideal choice for residential and light commercial boiler systems.
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