Floats versus Displacers

Following are the major points of distinction between floats and displacers:

  1. “Float Switches are available with a glandless design and are capable of fail safe operation in extreme process conditions, unlike displacers, which if the torque tube fails can provide a leak path.”

  2. A float generally rides above the surface of liquid whereas a displacer remains either partly or totally immersed in process liquid.

  3. Displacer switches are considered to be additionally stable and dependable as compared to standard float level switches in case of turbulent, surging, frothy and foamy services. However in case of refineries, the use of displacers is decreasing owing to their high installation cost and inaccurate performance due to process density changes. In these applications, float level switches have been found to be reliable and useful.

  4. Settings of displacers can be changed very easily since they can be shifted at any place along the length of the suspension cable. Moreover, these level devices have the provision of interchangeability between tanks. This is due to the fact that the differences in process density can be endured by varying the tension of the spring attached to the displacers.

  5. Testing the appropriate working of a displacer switch is much easier than a customary float level switch since the former requires just lifting of a suspension whereas the latter necessitates filling of liquid in the tank upto the actuation mark.

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