McDonnell & Miller 157S-R-M Pump Controller

The McDonnell & Miller 157S-R-M (Part Number 177306) is a heavy-duty, float-operated low water cut-off and pump controller designed for commercial and industrial steam boilers. This unit features an integral water column and alternate tappings to simplify installation on various boiler configurations. The 157S-R-M is functionally identical to the 172817, utilizing a snap-acting SPDT switch that eliminates the need for mercury while providing reliable boiler pump control and low-water safety shutdowns. Constructed with a Monel bellows for superior corrosion resistance and high-temperature durability, this controller manages pressures up to 150 PSI. The manual reset mechanism ensures that a technician must physically inspect the system after a low-water event before the burner can be re-engaged, providing a critical layer of safety for high-output steaming applications.

• Dual Switch Functionality: Integrated SPDT switches for simultaneous boiler feed pump management and low water alarm/cut-off.
• Manual Reset Safety: Prevents automatic burner restarts after a low-water condition, requiring professional site verification.
• Simplified Piping: Specialized alternate tappings and integral water column reduce field labor and component count.
• Durable Construction: Heavy-duty Monel bellows and mercury-free snap switches designed for long-term HVAC professional use.
• Universal Compatibility: Engineered for steam boilers of any steaming capacity with high-pressure requirements.

• Is the 157S-R-M a direct replacement for older mercury models? Yes, this snap-switch version replaces legacy mercury-tube controllers like the 157-R-M without requiring significant piping modifications.
• What is the difference between 157S-R-M and 172817? There is no functional difference; 172817 is the specific manufacturer part number for the 157S-R-M model configuration.
• Does this unit handle high-pressure steam? This controller is rated for steam boiler safety applications up to a maximum operating pressure of 150 PSI.

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