McDonnell & Miller 157S-MD Pump Controller

Secure high-performance water level management with the McDonnell & Miller 157S-MD Pump Controller (Part Number 175412), a heavy-duty combination low water cut-off and pump controller designed for industrial and commercial steam boilers. Engineered for maximum differential operation, this model is built to prevent nuisance burner shutdowns caused by volatile, fluctuating water lines, making it an essential component for high-demand boiler water level control. The unit features built-in snap-acting SPDT switches that provide high-temperature reliability and precise electrical response without the use of mercury, ensuring a safer work environment for technicians and compliant field installations.

The McDonnell & Miller 175412 is housed in a rugged float chamber with an integral water column, simplifying the piping process and providing a stable environment for level sensing. Its monel bellows construction offers superior corrosion resistance against aggressive boiler chemistries, while the 150 PSI maximum pressure rating ensures durability across various steaming capacities. Whether you are performing a head mechanism replacement or a new system integration, this controller’s manual reset capability (where applicable via the M-MD designation) adds a critical layer of safety by requiring a technician's inspection before the burner can cycle back on after a low-water event.

• Maximized System Stability: The maximum differential operation allows for greater separation between pump start and stop points, reducing cycling and equipment wear.
• Dual-Function Reliability: Operates as both a pump controller and a low water cut-off (LWCO) with an alarm actuation circuit.
• Industrial-Grade Materials: Features a monel bellows and a durable float designed to withstand high-pressure steam environments.
• Steam System Integration: Includes an integral water column with tappings for gauge glass and tri-cocks to maintain visual water level monitoring.
• Versatile Application: Suitable for boilers of any steaming capacity up to a maximum operating pressure of 150 PSI.

Common Questions

What is the purpose of the 'Maximum Differential' feature in the 157S-MD?
The "MD" designation indicates a wider operating range between the pump-on and pump-off levels. This is specifically designed for boilers with rapidly fluctuating water lines to prevent the burner from cutting off prematurely due to momentary surges or "hunting" in the water column.

Can I use the 157S-MD to replace older mercury switch models?
Yes, the snap-acting SPDT switch assembly in the 157S series is the direct mercury-free replacement for legacy McDonnell & Miller 157 models. It provides the same control logic while meeting current environmental and safety standards.

Does this unit come with a water column?
Yes, unlike the 150S series which requires a separate column or external mounting, the 157S series features an integral water column body, which allows for direct mounting of water gauge sets and tri-cocks.

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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.