McDonnell & Miller 150S-M-MD Controller

The McDonnell & Miller 150S-M-MD Controller (Part Number 172802) is a specialized combination low water cut-off and pump controller designed for commercial and industrial steam boiler applications. This model is engineered with maximum differential operation, which is critical for preventing nuisance burner shutdowns in low-pressure systems by allowing for a wider operating range between the pump-on and pump-off points. As a manual reset unit, it requires physical intervention to restart the burner following a low-water condition, ensuring a technician can inspect the system for faults before resuming operation.

Built for durability in high-temperature environments, the 150S-M-MD utilizes a Monel bellows for superior corrosion resistance and a snap-acting SPDT switch assembly. This mechanical float-operated control supports a maximum pressure of 150 PSI and features a dedicated pump control switch (SPST) alongside the low water cut-off and alarm switch (SPDT). The 172802 is an essential component for contractors maintaining boiler water level safety and ensuring consistent feed pump cycling across varying steaming capacities.

• Maximum Differential Logic: Reduces short-cycling and nuisance trips by optimizing the water level spread, perfect for systems with sensitive pressure fluctuations.
• Corrosion Resistance: High-grade Monel bellows extend the service life of the float mechanism in harsh steam environments.
• Manual Safety Reset: Integral manual reset SPDT switch forces a system check after a low-water event, enhancing site safety.
• Simplified Wiring: Features distinct snap-action switches for pump control and alarm actuation, streamlining integration with the burner circuit.
• High Pressure Rating: Rated for up to 150 PSI (10.5 kg/cm2), providing industrial-grade protection for high-pressure steam service.

What is the difference between the 150S-MD and the standard 150S?
The "MD" (Maximum Differential) model provides a wider water level differential between the pump-on and pump-off levels compared to the standard 150S. This is specifically used to prevent the burner from tripping during rapid water level surges or in low-pressure applications where a tighter differential causes nuisance cycles.

Can this unit be used for hot water boilers?
While Series 150S units are primarily designed for steam boilers with a separate water column, always verify the specific piping requirements and pressure ratings for your application before installation.

Is the head mechanism replaceable?
Yes, the head mechanism can be replaced without disturbing the 1" NPT piping connections, provided the body casting remains in good condition. Use the 150S-M-MD-HD for lead mechanism-only replacements.

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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.