McDonnell & Miller 51-2 Mechanical Water Feeder & Low Water Cut Off, 35 PSI, 1″ NPT (Part No. 135000)

Description

The McDonnell & Miller 51-2 (Part Number 135000) is a combination mechanical water feeder and low water cut off engineered for reliable, automatic protection of low pressure steam and hot water boilers. By integrating both water feeding and low water cut off functions into a single, compact unit, the 51-2 simplifies installation, reduces potential leak points, and ensures continuous boiler protection without the need for separate devices.

When boiler water drops to a low level, the snap-acting SPDT (Single-Pole, Double-Throw) switch immediately cuts power to the burner, preventing dry-fire damage. Simultaneously, the mechanical water feeder automatically replenishes the boiler with fresh make-up water, restoring safe operating levels. Once the proper water level is re-established, normal boiler operation resumes.

Key Features

• Combination mechanical water feeder and low water cut off in one unit
• Designed for low pressure steam and hot water boiler applications
• Maximum vessel pressure: 35 PSI
• 1″ NPT connections for straightforward installation
• Snap-acting SPDT switch for fast, reliable burner cut off response
• Automatic make-up water feeding restores safe boiler water levels
• Reduces installation complexity by combining two critical safety functions
• Part Number: 135000

Specifications

• Brand: McDonnell & Miller (Xylem)
• Model: 51-2
• Part Number: 135000
• Application: Low pressure steam and hot water boilers
• Maximum Vessel Pressure: 35 PSI
• Connection Size: 1″ NPT
• Switch Type: Snap-acting SPDT

Why Choose the McDonnell & Miller 51-2?

McDonnell & Miller, a trusted Xylem brand, has been manufacturing boiler controls and protection devices for decades. The 51-2 reflects that legacy of quality, offering installers and building engineers a dependable, code-compliant solution for boiler low water protection and automatic water feeding. Its straightforward 1″ NPT connections make retrofitting into existing systems easy, while the snap-acting SPDT switch ensures the burner is shut down without delay when water levels fall dangerously low.