Some of the most important factors to consider when choosing a float switch or level sensor is chemical compatibility and material selection. From potable water to the highly corrosive acids, level sensors are necessary for measuring a near-endless number of liquid chemicals. Obviously, a switch used for the former might not necessarily be ideal for the latter, but the material selection process is much more complicated than a simple ādrinking water versus acidā dichotomy.
There are dozens of materials common in the manufacture of float switches and level sensors, each with its own particular strengths and weaknesses in relation to specific applications and chemicals. Stainless steel, for instance, is a versatile material which is highly resistant to wear and corrosion from a number of different chemical compounds; however use of stainless steel should be avoided in wastewater treatment applications where ferric chloride is present at significant levels, as it can be highly corrosive even to stainless steels. Ceramic or epoxy-molded components would be ideal in such an environment. Here is a list of some of the most prevalent float switch materials in standard use, along with their common applications and chemical compatibilities. Please note that this is an extremely cursory guide (a more comprehensive chart is available in this pdf file).
Stainless Steel
Stainless steelās durability makes it ideal for high temperature conditions, and it holds up well with many highly corrosive chemicals. Itās also compatible with a number of sanitary and washdown conditions, making it frequently used in medical and food processing applications. Compatible chemicals include:
- Acetone
- Ammonia
- Coffee
- Gasoline
- Most oils
- Bronze and copper plating solutions
Brass
Brassās resistance to corrosion from gasoline and other petroleum-derived products 
makes it common in generator and hydraulic applications. Compatible chemicals include:
- Ether
- Butane
- Hexane
- Paraffin (kerosene)
- Turpentine
Buna-N (Nitrile Rubber)
Buna-N floats provide excellent buoyancy in petroleum fluids and oils, while also providing chemical compatibility with many dilute acids and bases. Compatible chemicals include:
- Ethyl alcohol
- Most ammonium compounds
- Machine lubricants
- Diesel fuel
- Salt water
Polypropylene
Polypropylene is a good choice for most generic applications, also holding up well in acidic and alkali conditions. High heat environments, however, should be avoided. Chemical compatibilities include:
- Citric acid
- Diesel fuel
- Photographic solutions
- Salt brine
- Paper waste (white liquor & water)
- Formaldehyde (40%)
Kynar
Kynar is a high-purity plastic commonly used in food handling, scientific applications, and environments with chemical solvents. Chemical compatibilities include:
- Bromine
- Chlorine water
- Aqueous solutions
- Potassium nitrate
- Vinegar
- Tannic acids
- Mineral spirits