Interface level switches are used to monitor the level of two liquids with different specific gravity values. When two different liquids are contained within the same tank, but are unable to mix with each other, an emulsion layer forms and creates a barrier between the two liquids. When two insoluble materials mix, the liquid with the heavier molecules will sink to the bottom while the lighter ones will stay on top, oil and water is perfect example of this.

Underground cement basins, wash pits, or any area that collects runoff of different liquids will often need to be pumped out. In the case of oil and water, the float on an interface liquid level sensor will sink through the oil but float on the water level allowing clear indication of the interface level. This can allow pumps to siphon off the oil to be reclaimed or recycled. Other applications use water or steam to help extract and clean the oil that comes from a well, and can even be used to help transport it. However the water must then be separated through a process appropriately called separation. Separation is used to remove the additives, solvents, catalysts, impurities, etc. Interface float level switches are critical to the operation of these difficult applications.

How does it work…

An interface level float is weighted so it’s heavy enough to sink through the oil and float on the water to monitor the level. Another float can be placed on the shaft that is able to measure the level of the second layer or total tank level. This float, an oil tank level sensor for example, is able to monitor the rising or falling levels and signal an alarm or even start a pump. Standard interface floats are weighted at a 0.95 specific gravity, but other weights are available upon request for various types of liquids.


  • Separators
  • Coking Drums
  • Heater Treaters
  • Sludge Thickeners
  • Free-water Knock-out
  • Regenerators
  • Filtration Systems

Series 1000 Stainless Steel

  • Small diameter floats
  • Up to 6 feet long

Series 2000 Stainless Steel

  • Large diameter floats
  • Up to 12 feet long*

*certain configurations available over 12 feet – call to discuss.

Series 1000 Brass & Buna

  • Small diameter floats
  • Up to 6 feet long

Series 2000 Brass & Buna

  • Large diameter floats
  • Up to 12 feet long
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