Examples of slosh shields.

Water is by no means the only fluid with which float switches are used. Thus, it is essential to know not only the specific gravity of the float, but also that of the fluid used in the application. The fluid's specific gravity must be greater than that of the float at the application's maximum temperature. Specific gravities of floats used for liquid level sensing can range from .45 to .85, depending upon size and the material they're made of.

Knowing a bit about specific gravity also makes it possible for engineers to design floats that differentiate between two liquids. Such floats, called interface floats, sink in one liquid and float in another. A typical application would be one in which a tank holds both oil and water, but you're only concerned with the water level. The specific gravity of the oil would be between 0.8 and 0.9 and that of water is 1.0. So a float with the specific gravity of 0.95 would sink in the oil and float in the water. Buna-N and polypropylene full-size floats can be modified to meet this demand.

Temperature, both maximum and minimum must also be considered. For example, 316 stainless steel is ideal for high-temperature applications up to 250°C. On the other hand, polypropylene should only be used where it will be subjected to temperatures of 105° or lower. Other commonly used switch materials (and their corresponding maximum temperatures) include; brass (130°C); Buna-N, or Nitrile, (120°C); PBT, or Polybutylene Terephthalate, (120°C); Polysulfone, or PSU, (148°C); Kynar (105°C); and Teflon® PTFE (260°C). As to the other end of the temperature range, Buna-N, also called Nitrile, can withstand the lowest temperatures, down to -50°C. Teflon® is a registered trademark of E.I. duPont de Nemours and Company.

• Click here to read more about the science of selection process.
• Click here to read more about the benefits of the selection process.

Contact Madison today to learn more about our liquid level float switch offerings!