Description
The Xylem-McDonnell & Miller 150S-MD-HD is a combination low water cut-off and pump controller designed for steam boiler protection and automatic pump management. This listing covers the Head Mechanism Only (Part Number 173103), making it an ideal replacement component for existing 150S-MD-HD installations without the need to replace the entire assembly.
Product Overview
The 150S-MD-HD features a snap-acting SPDT (Single-Pole, Double-Throw) switch with Maximum Differential (MD) operation, providing reliable and precise switching action for both low water cut-off protection and pump control functions. McDonnell & Miller’s trusted float-operated design has been a standard in the hydronic and steam heating industry for decades, ensuring boiler safety and operational efficiency.
Key Features
- Combination low water cut-off and pump controller in a single unit
- Snap-acting SPDT switch for reliable, positive switching action
- Maximum Differential (MD) operation for wider switching differential between pump-on and cut-off levels
- Head Mechanism Only — ideal for replacement without disturbing existing piping connections
- Part Number 173103 for easy cross-referencing and ordering
- Float-operated design for dependable water level sensing
- Suitable for steam boiler low water protection and automatic pump control applications
- Manufactured by Xylem-McDonnell & Miller, a trusted name in boiler controls
Application
The 150S-MD-HD is engineered for use on steam heating boilers where both low water cut-off protection and automatic pump control are required. The Maximum Differential (HD) head mechanism is specifically designed for applications requiring a greater differential between the pump-start and low water cut-off levels, reducing short-cycling and improving system reliability. The head-only configuration allows technicians to replace the control mechanism while retaining the existing body and piping, minimizing downtime and installation costs.
Why Choose McDonnell & Miller
McDonnell & Miller, a brand under Xylem, has been a leading manufacturer of boiler controls and low water cut-offs for over a century. Their products are widely specified by engineers and trusted by HVAC professionals for dependable boiler safety and pump control in residential, commercial, and light industrial applications.
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