McDonnell & Miller 150S-MD-HD Controller

The McDonnell & Miller 150S-MD-HD (Part Number 173103) is a high-performance combination low water cut-off and pump controller head mechanism designed for demanding commercial and industrial steam boiler applications. This specific model features maximum differential operation, a critical function that prevents nuisance burner shutdowns in systems with fluctuating water levels or low-pressure environments. By providing a wider 7/8-inch differential between the pump-on and pump-off points, it stabilizes cycling and ensures consistent boiler feed pump control. Built for durability, the unit incorporates a Monel bellows for superior corrosion resistance and heavy-duty snap-acting SPDT switches capable of managing high-temperature service up to 150 PSI. As a "head mechanism only," this 173103 unit allows for rapid field replacement without the need to break existing piping, significantly reducing labor hours and system downtime. It integrates seamlessly with both Series 150S and 157S assemblies to provide reliable LWCO protection and alarm actuation for any steaming capacity.

Key Benefits for High-Pressure Steam Systems

• Reduces Nuisance Tripping: The maximum differential mechanism provides a broader range between switching points, ideal for low-pressure boilers prone to water surges.
• Simplified Maintenance: Design as a replacement head mechanism allows technicians to swap internal components quickly by removing the casting bolts, preserving the original body and piping.
• Enhanced Corrosion Resistance: Utilizing a Monel bellows ensures long-term reliability in harsh boiler water environments.
• Flexible Control Logic: Includes a snap-acting SPDT switch for simultaneous low water cut-off protection and alarm signaling.
• Versatile Application: Rated for up to 150 PSI, making it suitable for a wide variety of commercial steam boiler configurations.

Common Technical Questions

What is the primary advantage of the MD (Maximum Differential) model versus the standard 150S?
The MD model is specifically engineered to handle boilers that experience rapid level fluctuations. By increasing the differential between the pump cycle points, it prevents the burner from cycling unnecessarily, which reduces wear on the motor starters and the burner itself.

Can the 150S-MD-HD be used on a manual reset system?
This specific head mechanism (173103) is typically configured for automatic reset. If your application specifically requires manual reset to comply with local boiler codes, you must ensure the switch assembly is compatible with the manual reset housing or select the 'M' suffix model.

Is the float included with the 173103 head mechanism?
No, the 150S-MD-HD includes the head mechanism only. The float and rod assembly (SA150-11) and the casting are sold separately or reused from the existing installation.

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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.