Xylem-McDonnell & Miller 51-S-2 Mechanical Water Feeder & Low Water Cut Off, 35 PSI, 1″ NPT (Part No. 135900)

Description

Xylem-McDonnell & Miller 51-S-2 Mechanical Water Feeder and Low Water Cut Off

The Xylem-McDonnell & Miller 51-S-2 (Part Number 135900) is a combination mechanical water feeder and low water cut off designed to protect low pressure steam and hot water boilers. By integrating both functions into a single, reliable unit, the 51-S-2 automatically maintains proper boiler water levels while simultaneously providing critical low water protection — helping to prevent costly boiler damage and unsafe operating conditions.

How It Works

The 51-S-2 uses a float-operated mechanism to monitor boiler water levels continuously. When the water level drops below the safe operating threshold, the snap-acting SPDT switch cuts off the burner to prevent dry firing. Simultaneously, the mechanical water feeder automatically adds make-up water to restore the proper level, minimizing manual intervention and keeping the boiler operating efficiently.

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 pipe connections for straightforward installation
• Snap-acting SPDT (Single-Pole Double-Throw) switch for reliable burner cut off
• Float-operated mechanical design — no external power required for water feeding function
• Durable construction built to McDonnell & Miller’s trusted quality standards
• Part Number: 135900

Specifications

• Model: 51-S-2
• Part Number: 135900
• Brand: Xylem-McDonnell & Miller
• 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-S-2?

McDonnell & Miller, a trusted Xylem brand, has been manufacturing boiler controls and water feeders for decades. The 51-S-2 simplifies boiler room installations by combining two essential safety and maintenance functions into one compact assembly. It is an ideal solution for residential and light commercial boiler systems where reliable low water protection and automatic water makeup are required.