McDonnell & Miller 157S-RLS-MD Control

The McDonnell & Miller 157S-RLS-MD (Part Number 177251) is a high-performance mechanical combination low water cut-off and pump controller designed for commercial and industrial steam boilers. Engineered for high-pressure applications up to 150 psi, this unit features a maximum differential operation that effectively prevents nuisance burner shutdowns in systems experiencing rapid water level fluctuations. Its integral water column design simplifies installation by providing a stable environment for the float and allowing for the direct mounting of gauge glass and tri-cocks via alternate tappings.

This controller utilizes a monel bellows for superior corrosion resistance and features high-temperature snap-action switches. The internal configuration includes a single pole, single throw (SPST) switch for precise pump control and a single pole, double throw (SPDT) switch for reliable low water cut-off and alarm actuation. This manual reset model ensures that the system requires technician intervention following a low water event, providing an essential safety layer for high-steaming capacity boilers.

Key Benefits for the Contractor:

• Includes alternate tappings for flexible gauge glass and tri-cock mounting configurations.
• Maintains maximum differential to eliminate short-cycling and nuisance trips in low-pressure steam systems.
• Equipped with a monel bellows to withstand harsh boiler feed water chemistry and prevent premature failure.
• Dual-function snap-action switches provide dedicated circuits for both the boiler feed pump and safety shutdown.
• Identical cross-reference to ITT 177251 for seamless drop-in replacement on existing water columns.

Common Questions:

How does the maximum differential feature improve boiler performance?
The "MD" designation indicates a larger operating range between the pump-on and pump-off points. This compensates for the narrowing of setpoints at lower pressures, preventing the boiler pump from cycling too frequently.

Is this unit compatible with high-temperature steam applications?
Yes, the McDonnell & Miller 157S-RLS-MD is built with heavy-duty components and snap-action switches specifically rated for high-temperature steam boiler service up to its 150 psi maximum rating.

What is the difference between this and the standard 157S model?
The 157S-RLS-MD includes a manual reset mechanism and a maximum differential switch, whereas standard models may feature automatic resets and standard operating differentials.

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.