McDonnell & Miller 150S-MD Controller

The McDonnell & Miller 150S-MD (Part Number 171802) is a heavy-duty combination low water cut-off and pump controller designed specifically for commercial and industrial steam boiler applications. This model features a snap-acting SPDT switch with Maximum Differential operation, which is critical for preventing rapid pump cycling in high-demand systems. It is engineered to maintain precise water levels up to a maximum pressure of 150 psi (10.5 kg/cm²). The "MD" configuration allows for a wider variation between the pump-on and pump-off levels compared to standard 150S units, making it ideal for systems with fluctuating loads. Built with a rugged cast iron body and a monel bellows, this controller ensures long-term reliability in harsh boiler room environments. For technicians managing steam heating systems, this unit provides essential protection against dry-firing while simultaneously regulating the boiler feed pump to ensure continuous operation and system stability.

• Maximum Differential Control: Prevents short-cycling by allowing a larger spread between pump start and stop points.
• Snap-Acting SPDT Switch: Delivers crisp electrical contact to reduce arcing and extend the service life of the LWCO controller.
• Dual Functionality: Operates as both a primary low water cut-off and a pump level controller for streamlined installation.
• Field-Proven Reliability: The robust mechanical linkage is designed to withstand high-pressure steam environments without frequent recalibration.

Common Technical Questions

How does the Maximum Differential (MD) model differ from the standard 150S?
The McDonnell & Miller 150S-MD provides a wider operating range between the pump-on and pump-off activations. This is specifically used to prevent the feed pump from cycling too frequently in systems where water levels fluctuate rapidly.

What is the maximum pressure rating for the 171802 controller?
This unit is rated for a maximum boiler pressure of 150 psi. Exceeding this limit can compromise the integrity of the bellows and the accuracy of the level control.

Can this unit be used for both high-voltage and low-voltage applications?
Yes, the snap-acting switches are designed to handle various electrical loads, but always verify the specific amp draw of your boiler feed pump against the manufacturer's electrical ratings before wiring.

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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.