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Mercoid Series 391

Series 391/393/394 Side Mounted-Chamber Type Level Control

Compact, Low Cost, Hermetically Sealed Snap Switch Option

Series 391/393/394Heavy duty and low cost is the perfect description for the 391 Series level control. Stainless steel switching mechanism uses gravity return action instead of springs for long life. Weatherproof enclosure is standard. Welded steel chamber is good for 650 psig (45 bar) at 600°F (315°C).



  • Service:Compatible liquids.
  • Wetted Materials:Body: carbon steel; Float and Trim: 303 SS, 304 SS, 316 SS, and 430 SS.
  • Temperature Limits:Process: 600°F (315.6°C). Heat fins should be used for process temperatures above 500°F (260°C) with mercury switches, 400°F (204°C) with snap switches, and 350°F (176.7°C) with hermetically sealed snap switches.
  • Pressure Limits:800 psig (55 bar) at 100°F (37.7°C), 650 psig (45 bar) at 600°F (315.6°C). Higher ratings available.
  • Enclosure Rating:NEMA 4X. Optional general purpose or explosion-proof.
  • Switch Type:SPDT snap switch, hermetically sealed snap switch or mercury switch. Optional DPDT.
  • Electrical Rating:Snap Switch: 12A @ 120 VAC, 5A @ 240 VAC, 0.5A @ 125 VDC resistive, 0.25A @ 250 VDC resistive. Hermetically Sealed Snap Switch: 5A @ 125 VAC, 5A @ 240 VAC, 5A @ 30 VDC resistive. Mercury Switch: 4A @ 120 VAC/DC, 2A @ 240 VAC/DC. Higher contact ratings available for the mercury switch.
  • Electrical Connections:Screw terminal.
  • Conduit Connection:3/4″ female NPT.
  • Connections:1″ female NPT. Optional 1″ socket weld hub or flange connections.
  • Mounting Orientation:Vertical.
  • Weight:10 lb (4.5 kg).
  • Agency Approvals:UL, none on HM switch.
  • Specific Gravity:0.8 minimum. Optional 0.7 minimum.