McDonnell & Miller 150S Switch

The McDonnell & Miller 150S Switch (Part Number 171702) is a heavy-duty combination low water cut-off and pump controller designed for commercial and industrial steam boiler applications. As a veteran-preferred mechanical water level control, this unit features a snap-acting SPDT switch assembly that provides precise low water cut-off and alarm actuation. The 150S series is engineered for boilers of any steaming capacity, supporting a maximum pressure of 150 psi (10.5 kg/cm²). Its construction includes a corrosion-resistant Monel bellows and high-temperature snap-action switches, ensuring reliable performance in demanding boiler room environments.

For contractors performing boiler control replacement, the 171702 serves as a direct float-type controller with 1" NPT connections. It integrates a single pole, single throw (SPST) switch for dedicated pump control alongside the SPDT switch for safety limits. This automatic reset model prevents nuisance burner shutdowns and is a standard for professional HVACR maintenance. Professionals should note that this Xylem McDonnell & Miller head mechanism is compatible with 1" equalizing piping and is often utilized as a primary or secondary safety control in systems exceeding 400,000 BTU/hour.

• Dual-Function Reliability: Operates as both a pump controller and a low water cut-off (LWCO) to streamline boiler management.
• High-Temperature Durability: Equipped with snap-acting switches and a Monel bellows for long-term resistance to heat and corrosion.
• Maximum Pressure Rating: Rated for 150 psi steam pressure, making it suitable for a wide range of industrial boilers.
• Universal Application: Designed to fit boilers of any steaming capacity with standard 1" NPT pipe connections.

What is the difference between the 150 and the 150S?
The 150S series utilizes modern snap-acting switches, which are highly resistant to vibration and high temperatures, whereas older 150 models originally featured mercury switches which are now largely obsolete.

Can I use the 171702 as a lead/lag pump controller?
While the 171702 features a dedicated pump control circuit, it is typically used for a single pump. For advanced sequencing or lead/lag operations, a separate alternator or multi-stage controller may be required in series.

Is the 171702 compatible with manual reset requirements?
This specific part number is an automatic reset model. If your local code or application requires a manual reset, you would typically look for the "M" suffix models, such as the 150S-M.

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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.