McDonnell & Miller 150S-M-HD Controller

The McDonnell & Miller 150S-M-HD Controller (Part Number 173203) is a heavy-duty, replacement head mechanism designed for industrial and commercial steam boiler applications. This combination low water cut-off and pump controller features a snap-acting manual reset switch, providing essential safety redundancy by preventing the burner from firing if a low-water condition occurs. Engineered for durability, the unit utilizes a corrosion-resistant Monel bellows to ensure reliable operation in high-temperature environments up to 150 PSI. As a direct drop-in replacement, it is functionally identical to the 172809 model, allowing contractors to service 150S Series water level controls without disturbing the existing equalizing piping or main body casting.

This head mechanism includes a manual reset SPDT switch that requires physical intervention to restart the burner, ensuring the cause of a low-water event is investigated first. The snap-acting switch mechanism provides precise differential control for boiler feed pumps, maintaining tight water level tolerances and preventing short-cycling in high-demand systems. For technicians performing routine maintenance or emergency repairs, the 150S-M-HD replacement head offers a streamlined solution to restore system integrity while maintaining compliance with high-pressure safety standards.

• Dual-Function Control: Operates as both a primary or secondary low water cut-off and a dedicated pump controller for steam systems.
• Manual Reset Safety: The integrated manual reset SPDT switch provides an extra layer of protection by requiring a local check before system reactivation.
• Monel Bellows Construction: High-grade corrosion-resistant bellows extend the component's operational life in harsh boiler water conditions.
• Direct Field Replacement: Designed as a "head only" mechanism to replace Part Number 173203 and 172809 without needing to re-pipe the entire unit.
• High Pressure Rating: Rated for service up to 150 PSI (10.5 kg/cm2), making it suitable for a wide range of commercial boiler configurations.

Is the 150S-M-HD compatible with older 150 Series bodies?
Yes, this replacement head mechanism is designed to fit standard Series 150 and 150S bodies. It allows you to upgrade or repair the internal switch and bellows assembly without removing the main housing from the steam equalizing lines.

What is the difference between the 150S-M-HD and the 150S-HD?
The "M" designation indicates a manual reset switch. While the standard 150S-HD features an automatic reset, the 150S-M-HD (173203) requires a technician to manually press the reset button after a low-water cutout occurs.

Can this be used for both pump control and alarm actuation?
The snap-acting SPDT switch is specifically configured for combination service, handling burner cutout, alarm signaling, and boiler feed pump operation across 120V or 240V circuits.

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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.