{"title":"McDonnell \u0026 Miller","description":"\u003cp\u003e\n  Shop heavy-duty \u003cstrong\u003eMcDonnell \u0026amp; Miller\u003c\/strong\u003e boiler safety controls, low water cut-offs (LWCO), liquid flow switches, and automatic boiler feed pump controllers. Trusted by engineers and mechanical contractors for decades, McDonnell \u0026amp; Miller products provide dependable over-temperature protection, precise water level regulation, and fail-safe flow detection in low- and high-pressure steam and hydronic boiler applications.\n\u003c\/p\u003e","products":[{"product_id":"mcdonnell-miller-149400-67-lwco-quick-hook-up","title":"McDonnell \u0026 Miller 149400 67-LWCO-QUICK HOOK UP","description":"\u003cp\u003eThe \u003cstrong\u003eMcDonnell \u0026amp; Miller 149400 (Model 67-LQ) Low Water Cut-Off\u003c\/strong\u003e is the industry standard safety control engineered for low-pressure steam boilers. Designed with the patented \"Quick Hook-Up\" configuration, this float-type control hooks directly into existing gauge glass tappings to cut power to the burner instantly if the boiler water level falls to a critically low line, preventing structural dry-firing damage.\u003c\/p\u003e\n\n\u003ch3\u003eKey Features\u003c\/h3\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003eQuick Hook-Up Installation:\u003c\/strong\u003e Engineered with specialized dual-coupling union fittings that tap directly into standard gauge glass connections without requiring complex pipe cutting or system drain-downs.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eIntegrated Blow-Down Valve:\u003c\/strong\u003e Features a robust built-in blow-down valve assembly designed to quickly flush out accumulated sediment and scale from the float chamber during routine maintenance.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eDual Switch Capability:\u003c\/strong\u003e Equipped with an auxiliary terminal configuration ready to power an automatic water feeder or trigger an external low-water alarm loop.\u003c\/li\u003e\n\u003c\/ul\u003e","brand":"McDonnell \u0026 Miller","offers":[{"title":"Default Title","offer_id":42935821664350,"sku":"MM-149400","price":237.0,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0663\/7151\/8558\/files\/McDonnell_and_Miller_149400_model_67_low_water_cut_off_quick_hook_up_dual_union_pipes_front_view.jpg?v=1782266221"},{"product_id":"mcdonnell-miller-172806-150s-m-lwco-wmagnetic-type-reset","title":"McDonnell \u0026 Miller  172806 150S-M LWCO W\/MAGNETIC TYPE RESET","description":"\u003cp\u003eThe \u003cstrong\u003eMcDonnell \u0026amp; Miller 172806 (Model 150S-M) Low Water Cut-Off and Pump Controller\u003c\/strong\u003e is a heavy-duty commercial boiler control engineered for low to medium pressure steam systems. Featuring a specialized manual reset with a magnetic-type mechanism, this control automatically monitors critical boiler water levels, safely cuts power to the burner during an emergency low-water event, and controls automatic feed pump sequencing to prevent catastrophic dry-firing.\u003c\/p\u003e\n\n\u003ch3\u003eKey Features\u003c\/h3\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003eMagnetic-Type Manual Reset:\u003c\/strong\u003e Provides positive, fail-safe lock-out protection during low-water conditions, requiring physical manual intervention to restart the burner system after a safety event.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eDual Function Operation:\u003c\/strong\u003e Combines a highly responsive low-water cut-off switch with an integrated, crisp-acting pump controller for complete water line sequencing.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eCommercial Durability:\u003c\/strong\u003e Engineered with a robust cast iron body and heavy-duty mercury-free switches designed to withstand demanding institutional mechanical room environments.\u003c\/li\u003e\n\u003c\/ul\u003e","brand":"McDonnell \u0026 Miller","offers":[{"title":"Default Title","offer_id":42935821697118,"sku":"MM-172806","price":788.0,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0663\/7151\/8558\/files\/McDonnell_and_Miller_172806_model_150S_M_low_water_cut_off_manual_reset_boiler_control_housing_front_view.jpg?v=1782265815"},{"product_id":"mcdonnell-miller-171702-150s-hi-pressure-level-control","title":"McDonnell \u0026 Miller 171702 150S High Pressure Low Water Cut-Off \u0026 Boiler Pump Controller (1 Inch NPT, 150 PSI)","description":"\u003ch2\u003eMcDonnell \u0026amp; Miller 171702 (Model 150S) Combination Low Water Cut-Off \u0026amp; Pump Controller\u003c\/h2\u003e\n\u003cp\u003e\n  Designed for primary or secondary low water fuel cut-off and automatic feed pump regulation on commercial and industrial steam boilers, the \n  \u003cstrong\u003eMcDonnell \u0026amp; Miller 171702 (Model 150S)\u003c\/strong\u003e is the industry-standard mechanical level controller for high-pressure steam applications. Operating at maximum steam pressures up to 150 PSI (10.5 kg\/cm²), this heavy-duty control features a rugged cast iron float chamber and corrosion-resistant Monel bellows seal isolation.\n\u003c\/p\u003e\n\u003cp\u003e\n  Unlike maximum-differential variants, the standard \u003cstrong\u003e150S\u003c\/strong\u003e features factory-calibrated standard switching levels to provide tight, responsive water line control. Its internal mechanism incorporates two heavy-duty snap action switches—a single pole, single throw (SPST) switch for direct boiler feed pump activation and a single pole, double throw (SPDT) switch for low water burner cut-off and alarm circuit operation.\n\u003c\/p\u003e\n\n\u003ch4\u003eKey Performance \u0026amp; Engineering Highlights:\u003c\/h4\u003e\n\u003cul\u003e\n  \u003cli\u003e\n    \u003cstrong\u003eStandard Switching Differential:\u003c\/strong\u003e Provides tight water line maintenance and rapid low-water burner shutdown protection.\n  \u003c\/li\u003e\n  \u003cli\u003e\n    \u003cstrong\u003eSealed Monel Bellows Isolation:\u003c\/strong\u003e Prevents steam, condensate, and boiler water contaminants from entering the switch housing, extending mechanical life.\n  \u003c\/li\u003e\n  \u003cli\u003e\n    \u003cstrong\u003eDual Snap Switches:\u003c\/strong\u003e Contains 1 SPST snap switch for feed pump control and 1 SPDT snap switch for low water fuel cut-off (LWCO) and alarm activation.\n  \u003c\/li\u003e\n  \u003cli\u003e\n    \u003cstrong\u003e1\" NPT Female Tappings:\u003c\/strong\u003e Standard 1\" female NPT side equalizing connections simplify rigid pipe mounting directly to the boiler shell or external water column.\n  \u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cp\u003e\n  ⚠️ \u003cstrong\u003eApplication Profile:\u003c\/strong\u003e Essential for commercial and industrial steam boilers of any steaming capacity requiring primary\/secondary low water fuel cut-off, automated boiler feed pump control, or high\/low level alarm signaling up to 150 PSI.\n\u003c\/p\u003e","brand":"McDonnell \u0026 Miller","offers":[{"title":"Default Title","offer_id":43041399865438,"sku":"MM-171702","price":1595.0,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0663\/7151\/8558\/files\/McDonnell_and_Miller_171802_150S-MD_Low_Water_Cut-Off_and_Boiler_Pump_Controller_1_Inch_NPT_150_PSI.jpg?v=1784749864"},{"product_id":"mcdonnell-miller-171802-150s-md-hi-press-level-control","title":"McDonnell \u0026 Miller 171802 150S-MD Low Water Cut-Off \u0026 Boiler Pump Controller (1 Inch NPT, Max Differential, 150 PSI)","description":"\u003ch2\u003eMcDonnell \u0026amp; Miller 171802 (Model 150S-MD) Combination Low Water Cut-Off \u0026amp; Pump Controller\u003c\/h2\u003e\n\u003cp\u003e\n  Engineered for primary or secondary low water fuel cut-off and automatic feed pump control on commercial and industrial steam boilers, the \n  \u003cstrong\u003eMcDonnell \u0026amp; Miller 171802 (Model 150S-MD)\u003c\/strong\u003e is a heavy-duty mechanical level controller designed for demanding high-temperature steam applications. Rated for operating steam pressures up to 150 PSI (10.5 kg\/cm²), this unit features a durable cast iron float chamber and heavy-duty Monel bellows construction for superior corrosion resistance and long operating life.\n\u003c\/p\u003e\n\u003cp\u003e\n  The \u003cstrong\u003e150S-MD\u003c\/strong\u003e model is factory-configured with a \u003cem\u003eMaximum Differential (MD)\u003c\/em\u003e operating profile, widening the switching distance between pump-off and burner-off settings to 1-3\/8\". This specialized differential setting compensates for setpoint shifts in low-pressure steam boilers (operating below 50 PSI), effectively eliminating rapid cycling and nuisance burner shutdowns caused by severe surging or rapidly fluctuating boiler water levels.\n\u003c\/p\u003e\n\n\u003ch4\u003eKey Performance \u0026amp; Construction Features:\u003c\/h4\u003e\n\u003cul\u003e\n  \u003cli\u003e\n    \u003cstrong\u003eMaximum Differential (MD) Tuning:\u003c\/strong\u003e Widened switching differential prevents rapid burner cycling and false trips in systems operating under 50 PSI.\n  \u003c\/li\u003e\n  \u003cli\u003e\n    \u003cstrong\u003eMonel Bellows Seal Isolation:\u003c\/strong\u003e Corrosion-resistant Monel bellows seal isolates mechanical switch linkages from harsh steam and boiler water environments.\n  \u003c\/li\u003e\n  \u003cli\u003e\n    \u003cstrong\u003eDual Heavy-Duty Snap Switches:\u003c\/strong\u003e Factory-equipped with one SPST snap switch for direct boiler feed pump activation and one SPDT switch for low water fuel cut-off and alarm signaling.\n  \u003c\/li\u003e\n  \u003cli\u003e\n    \u003cstrong\u003e1\" NPT Equalizing Tappings:\u003c\/strong\u003e Heavy-duty cast body with 1\" female threaded steam and water equalizing ports for solid pipe mounting directly to the boiler shell or external water column.\n  \u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cp\u003e\n  ⚠️ \u003cstrong\u003eApplication Profile:\u003c\/strong\u003e Recommended for commercial and industrial steam boilers of any steaming capacity requiring primary or secondary low water fuel cut-off, automated boiler feed pump control, or high\/low level alarm activation up to 150 PSI.\n\u003c\/p\u003e","brand":"McDonnell \u0026 Miller","offers":[{"title":"Default Title","offer_id":43041399930974,"sku":"MM-171802","price":1595.0,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0663\/7151\/8558\/files\/McDonnell_and_Miller_171802_150S-MD_Low_Water_Cut-Off_and_Boiler_Pump_Controller_1_Inch_NPT_150_PSI.jpg?v=1784749864"},{"product_id":"mcdonnell-miller-114400-fs4-3-flow-switch-1-npt","title":"McDonnell \u0026 Miller 114400 FS4-3 General Purpose Liquid Flow Switch (1 Inch NPT, SPDT, 160 PSI)","description":"\u003ch2\u003eMcDonnell \u0026amp; Miller 114400 (Model FS4-3) General Purpose Liquid Flow Switch\u003c\/h2\u003e\n\u003cp\u003e\n  Engineered for universal flow monitoring in commercial and industrial HVAC, hydronic, and process liquid piping networks, the \n  \u003cstrong\u003eMcDonnell \u0026amp; Miller 114400 (Model FS4-3)\u003c\/strong\u003e is a heavy-duty paddle-style liquid flow switch. Featuring a standard 1\" NPT male process connection and a single pole, double throw (SPDT) snap switch rated for 120\/240VAC operation, this unit automatically signals pumps, burners, or alarms when liquid flow starts or stops.\n\u003c\/p\u003e\n\u003cp\u003e\n  The FS4-3 incorporates a sealed Monel bellows and hardened stainless steel bearings to eliminate internal friction and maximize service life in continuous-duty applications. It comes factory-equipped with four trimmed stainless steel paddles (1\", 2\", 3\", and 6\") to fit pipe sizes ranging from 1\" up to 6\" diameter, making it one of the most versatile flow switches on the market.\n\u003c\/p\u003e\n\n\u003ch4\u003eKey Performance \u0026amp; Construction Highlights:\u003c\/h4\u003e\n\u003cul\u003e\n  \u003cli\u003e\n    \u003cstrong\u003eUniversal Pipe Fitting:\u003c\/strong\u003e Supplied with 4 interchangeable stainless steel paddles to accommodate 1\", 2\", 3\", and 6\" nominal pipe sizes.\n  \u003c\/li\u003e\n  \u003cli\u003e\n    \u003cstrong\u003eAdjustable Switch Sensitivity:\u003c\/strong\u003e Features an accessible sensitivity adjusting screw for fine-tuning flow activation thresholds on-site.\n  \u003c\/li\u003e\n  \u003cli\u003e\n    \u003cstrong\u003eSealed Monel Bellows Assembly:\u003c\/strong\u003e Isolates electrical snap components from fluid streams to ensure leak-free, corrosion-resistant operation.\n  \u003c\/li\u003e\n  \u003cli\u003e\n    \u003cstrong\u003eDual Electrical Knockouts:\u003c\/strong\u003e Enclosure features electrical knockouts on both sides for quick wiring from either orientation.\n  \u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cp\u003e\n  ⚠️ \u003cstrong\u003eApplication Profile:\u003c\/strong\u003e Ideal for water chillers, commercial boiler safety cut-offs, liquid heat exchange loops, water treatment systems, and pump proving circuits handling up to 160 PSI and fluid temperatures from 32°F to 300°F.\n\u003c\/p\u003e","brand":"McDonnell \u0026 Miller","offers":[{"title":"Default Title","offer_id":43041399996510,"sku":"MM-114400","price":280.0,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0663\/7151\/8558\/files\/McDonnell_and_Miller_114400_FS4-3_General_Purpose_Liquid_Flow_Switch_1_Inch_NPT.jpg?v=1784748301"}],"url":"https:\/\/nationalboilersupply.com\/collections\/mcdonnell-miller.oembed","provider":"National Boiler Supply","version":"1.0","type":"link"}