Chamber Mount Displacer Switches

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What Is a Displacer Switch?

A displacer switch is a mechanical point-level instrument that uses buoyancy to actuate an electrical or pneumatic switch.The sensing element (the displacer) is suspended within a pressure-rated external chamber. As liquid level changes,the change in buoyant force moves a magnetically coupled mechanism that snaps a switch—providing precise, repeatable, HI/LO trips without relying on electronics in the wetted path.

Omnitrol 663/664/666/668 (W)
666/668

Omnitrol 666C/668C

The Omnitrol 666/668(C) delivers compact, chamber-mounted displacer switching engineered for extreme duty environments to ensure fail-safe level protection on liquids — including low-specific-gravity hydrocarbons, solvents, and steam condensate.

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Omnitrol 664/666/668 (F)

Omnitrol 664F/666F/668F

The Omnitrol 664 / 666 / 668 (F) delivers rugged flanged chamber construction, factory specific-gravity calibration, and predictable switching differentials across a wide range of process fluids on pressurized vessels or bypass chambers.

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Omnitrol 663/664/666/668 (W)

Omnitrol 663/664/666/668 (W)

The Omnitrol 663 / 664 / 666 / 668 (W) provides a long welded external chamber, factory-set specific gravity calibration, and proven displacer actuation for accurate, drift-free switching in demanding services.

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Omnitrol 664/666/668 (F)

Omnitrol 764 / 766 / 768 (F)

The Omnitrol 764 / 766 / 768 (F) provides a dual-actuator displacer switch with a flanged connection designed for high-pressure service, clean alarm logic, and reliable pump start/stop control.

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Omnitrol 663/664/666/668 (W)

Omnitrol 764W / 766W / 768 (W)

The Omnitrol 764W / 766W / 768W delivers dual-actuator displacer switching inside a welded bypass chamber without adding vessel penetrations or gasketed joints.

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How It Works

  • A sealed side-mounted chamber houses a graphite (standard) or stainless steel displacer connected to a spring-loaded rod.
  • As level rises, buoyant force increases and lifts the displacer, shifting a magnet inside the head assembly.
  • A secondary magnet and snap-action mechanism toggle an SPDT/DPDT microswitch
  • Factory calibration to the process specific gravity (SG) sets the correct actuation points and differential.
  • No electronics required in the wetted path → immune to drift and suitable for harsh, hot, or hazardous services.

Where is Displacer Technology Most Effective?

High-pressure/high-temperature vessels (heaters, separators, steam drums): dependable shutdown and alarms where electronics struggle.

Pressurized or closed vessels — where side access isn’t possible or chamber installation is impractical.

Boilers and condensate systems — for high-temperature service where floats or electronics may fail.

Wastewater and sump applications — where turbulence, foam, or coating media can interfere with float or ultrasonic devices.

Floating roof and API 2350-compliant overfill systems — using dense displacers for accurate roof-height alarms.

Typical process conditions include pressures up to 1500 psig and temperatures to 500°F, with materials of construction such as stainless steel, graphite, porcelain, or lead, selected for compatibility and durability.

Where is Displacer Technology Most Effective?

  • High-pressure/high-temperature vessels (heaters, separators, steam drums): dependable shutdown and alarms where electronics struggle.
  • Low specific gravity liquids (LPG/NGLs, light solvents): displacers can be set to deliver small, predictable differentials at low SGs.
  • External bypass/chambers on pressurized tanks: isolate the instrument for safe service without opening the vessel.
  • Interface detection (oil/water in separators): long welded “W” or flanged “F” bodies can be factory-set for two-phase duty (per model limits).
  • Dual-point pump control (start/stop) or HI/LO protection can provide two independent set points in one chamber.

When to Choose Chamber-Mounted Switches vs. Top-Mounted Switches or Another Technology

Choose Omnitrol chamber-mounted displacer switches when the decision factors below apply:

  • Serviceability & Isolation: Side-mounted chamber can be valved off for maintenance—no tank entry required.
  • Pressure/Temperature Envelope: Chamber designs cover high pressure and elevated temperature ranges common in refining and chemical units.
  • Low-SG Performance: Published small switching differentials at low SGs minimize nuisance trips on light hydrocarbons.
  • Interface or Dual-point Control: Long welded or flanged bodies (W/F) support interface duties and dual actuators for pump control.
  • Hazardous Areas: Explosion-proof/vapor-proof housings with UL/CSA approvals ease compliance in classified locations.
Pick a different option when these apply:
  • Top-Mounted Displacer Swithces: Use when a side nozzle or external chamber isn’t available and the service allows top access with appropriate pressure class.
  • Ultrasonic/Microwave Barrier Switch: Prefer for non-contact solids detection, blocked chute/belt applications, or where vessel penetration must be avoided.
  • Capacitance Switch: Useful for clean fluids with stable dielectric properties and simple wiring needs; not ideal for wide SG swings.
  • Magnetostrictive or Radar Transmitter: Choose for continuous level measurement rather than binary HI/LO control.

Omnitrol Chamber-Mounted Families at a Glance

  • 666/668(C): Short welded, compact; excellent for low-SG and tight spaces; single point.
  • 664F/666F/668F: Flanged chambers; process-piping-ready; predictable, published differentials; single point.
  • 663/664/666/668(W): Long welded chambers; tailored differential and interface duty; single point.
  • 764/766/768(F/W): Dual actuators in one chamber for pump control and HI/LO protection.

Summary

Displacer switches provide rugged, drift-free point-level control using a purely mechanical, magnetically coupled mechanism. Omnitrol’s chamber-mounted portfolio combines pressure-rated external chambers, factory specific-gravity calibration, and broad hazardous-location approvals to deliver precise HI/LO and pump-control trips in demanding refinery, chemical, power, and water services. Choose chamber-mounted designs when you need high pressure/temperature capability, low-SG performance, serviceable isolation, interface detection, or dual setpoints in a single instrument.