The McDonnell & Miller 159S Controller (Part Number 178802) is a specialized combination low water cut-off and pump controller designed for heavy-duty commercial and industrial steam boiler applications. Operating at a maximum pressure of 150 psi, this unit integrates a float-operated mechanism with dual bi-metal snap acting switches to ensure precise level management. The configuration features one SPST switch dedicated to pump control and a second switch for low water cut-off and alarm actuation. Built with a corrosion-resistant Monel bellows, the 159S provides high-temperature reliability and automatic reset functionality, making it a rugged alternative to standard mercury switch models. This high-pressure level control is essential for maintaining the normal boiler water line and preventing dry-fire conditions in systems with separate water columns. Snap-Action Switch Reliability: High-temperature bi-metal switches eliminate the need for mercury while providing crisp, repeatable boiler pump control. Industrial Durability: The Monel bellows construction resists scale and corrosion, extending the service life in harsh steam environments. Versatile Integration: Features a 1" FIP connection and is compatible with various steam boiler level control piping configurations. Critical Safety: Acts as a primary low water cut-off to protect the burner circuit during low-level transients. Common Questions Is the McDonnell & Miller 159S a direct replacement for mercury switch models? Yes, the 159S uses snap acting switches designed to replace older mercury-style controllers in high-pressure applications up to 150 psi. What is the difference between the 159S and the 150S series? The 159S is specifically configured with two SPST switches for precise pump and cut-off sequencing, whereas other 150S variants may utilize SPDT configurations for different alarm requirements. Does this unit support automatic or manual reset? This specific model (178802) features automatic reset logic, restoring burner operation once the water level returns to the safe operating range above the cast line. 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.
