McDonnell & Miller 93-M Pump Controller

The McDonnell & Miller 93-M is a commercial-grade combination low water cut-off and pump controller designed specifically for steam boiler applications. Engineered for systems with a maximum steam pressure of 150 PSI, this unit features dual snap-acting manual reset SPDT switches. These switches provide decisive electrical contact, preventing the rapid cycling or "chattering" often found in mercury-free alternatives during turbulent water level conditions. The manual reset functionality is a critical safety requirement for many jurisdictions, ensuring that a low water condition is physically acknowledged by a technician before the burner is allowed to refire. This robust controller maintains precise water levels while providing a secondary safety failure point to protect the heat exchanger from dry-firing.

Technical Specifications & Features:

• Maximum Pressure: 150 psi (10.5 kg/cm²) for high-pressure steam reliability.
• Manual Reset Mechanism: Requires operator intervention following a low water event to ensure system integrity.
• Switch Configuration: Two SPDT snap-acting switches for simultaneous pump control and burner interruption.
• Proportional Control: Specifically calibrated for steam boiler water level control and low water safety.
• Easy Maintenance: Large float chamber design minimizes sediment buildup around the bellows.

Common Questions:

How do I wire the McDonnell & Miller 93-M for both pump control and low water cutoff?
The unit utilizes two independent SPDT switches. One switch is typically wired to the boiler feed pump starter, while the second switch is wired in series with the burner control circuit to break the limit string upon a low water condition.

Can the 93-M be used in hot water heating boilers?
This specific model is optimized for steam systems where a combination pump controller and LWCO is required. For hot water applications, ensure the pressure and temperature ratings align with your specific plant requirements.

What is the difference between the 93 and the 93-M?
The "M" designation identifies the manual reset version. While the standard 93 resets automatically once the water level is restored, the 93-M requires a technician to press the reset button to resume operation after a low water lockout.

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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.