McDonnell & Miller 157S-RBP-MD Pump Controller

The McDonnell & Miller 157S-RBP-MD Pump Controller (Part Number 176503) is a heavy-duty, float-operated combination low water cut-off and pump controller designed for commercial and industrial steam boilers. Engineered with an integral water column and monel bellows for superior corrosion resistance, this unit provides precise level management at operating pressures up to 150 psi. This specific model features maximum differential operation, which is critical for preventing nuisance burner shutdowns in low-pressure systems by widening the gap between the pump start and stop points. The inclusion of two integral conductance probes offers secondary redundant protection and enhanced sensing accuracy, a standard requirement for high-capacity steaming applications. For localized wiring, the controller provides alternate tappings (1" NPT and 1-1/4" FIP connections) and 1/2" NPT tappings for gauge glass and tri-cocks. This hardware utilizes a snap-acting SPDT switch to ensure reliable 120V/240V signal transmission for both pump activation and burner safety circuits.

• Maximum Differential Control: Optimized for systems where rapid water level fluctuations cause frequent cycling, ensuring consistent burner stability.
• Redundant Sensing Technology: Combines mechanical float operation with dual integral conductance probes for secondary low water protection.
• Corrosion-Resistant Internals: Features high-grade monel bellows to withstand aggressive steam environments and chemical treatments.
• Contractor-Friendly Installation: Designed with alternate tappings and a built-in water column to simplify mounting and eliminate the need for external equalizing manifolds.
• Snap-Acting Switches: High-temperature SPDT snap action switches provide decisive electrical contact for pump control and low water alarms.

What is the difference between the 157S and the 157S-RBP-MD?
The 157S-RBP-MD version includes maximum differential operation and two integrated 26,000-ohm sensitivity conductance probes. These probes provide a secondary layer of electronic sensing that the basic mechanical 157S lacks, making it suitable for applications requiring tighter level oversight and high-differential logic.

Can this unit be used on high-pressure steam boilers?
Yes, this controller is rated for a maximum pressure of 150 psi (10.5 kg/cm²), making it compatible with both low-pressure residential and high-pressure industrial steam applications.

Does this part involve manual or automatic reset?
The 157S-RBP-MD features an automatic reset configuration. Once the water level is restored to a safe operating point, the low water cut-off switch re-engages the burner circuit without technician intervention.

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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.