McDonnell & Miller 157S-R Controller

The McDonnell & Miller 157S-R (Part Number 176220) is a heavy-duty, float-operated combination low water cut-off and pump controller designed specifically for steam boilers with an integral water column. This model serves as the upgraded direct replacement for the McDonnell & Miller 157-R, transitioning from older mercury switch technology to reliable, bimetal snap-acting switches for enhanced safety and modern compliance. Built with a corrosion-resistant Monel bellows, this controller is engineered to withstand high-temperature service in both residential and industrial applications.

This unit features alternate tappings including 1/2" NPT connections for gauge glass and tri-cocks, plus a 1" FIP connection for streamlined integration into existing high-pressure systems. The internal mechanism includes two 120V switches: a single pole, single throw (SPST) switch dedicated to pump control and a single pole, double throw (SPDT) switch for low water cut-off and alarm activation. With a maximum pressure rating of 150 psi and automatic reset functionality, the 157S-R ensures consistent water level management and burner protection without the environmental hazards of mercury.

• Snap-Acting Switch Technology: Efficiently replaces legacy 157-R mercury units with high-sensitivity, vibration-resistant bimetal switches.
• Dual-Function Performance: Simultaneously manages boiler feed pump control and provides critical low water safety shutdown and alarm signaling.
• Durable Construction: Features Monel bellows and a robust float chamber with an integral water column for long-term reliability in harsh steam environments.
• Versatile Piping Options: Includes alternate tappings to accommodate various field installations and secondary site accessories like gauge sets.
• High Pressure Capability: Rated for systems up to 150 psi (10.5 kg/cm²), meeting the demands of commercial steaming capacities.

Common Questions

Is the 157S-R a drop-in replacement for the older 157-R model?
Yes, the 157S-R is specifically designed as the 157-R replacement. It maintains the same physical footprint and tapping locations but utilizes snap-switch mechanisms instead of mercury tubes.

What are the benefits of the alternate tappings on this part number?
The alternate tappings provide additional 1/2" NPT ports, allowing contractors to easily mount water gauge glasses and tri-cocks directly to the controller body without complex manifold piping.

Does this unit require a manual reset after a low water event?
No, this specific model (176220) is an automatic reset pump controller. Once the water level returns to a safe operating range, the switches will automatically reset the burner circuit.

This item is not eligible for free shipping.

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.