Understanding Chemical Compatibility
Liquid level switches and sensors measure all kinds of fluids, such as hot oils used in commercial kitchens, caustic chemicals used in processing equipment, liquid detergents and waxes in carwash locations, and black/grey water in sewage treatment plants. Material selection plays an important role in the selection of a liquid level switch/sensor because the material choice is dependent on the chemical compatibility of the liquid being sensed. For example, polypropylene is an excellent material that works well in most liquids, but will melt in high heat. 316 stainless steel is a highly durable material but not recommended for use with chlorine or sulfuric acid.
The key to selecting the correct float switch or sensor material that matches your liquid environment is to know or identify the chemicals and conditions of use. To determine the appropriate material in your level sensing application, ask the following questions:
- What is the tank and other materials in contact with the liquid made of?
- What concentration are the chemicals?
- What is the max temperature?
Common Sensor Materials
- 316 Stainless Steel
- Durable and compatible with many types of liquids, 316 stainless steel is frequently used in food processing, especially in high temperature applications, plating processes, medical applications and petrochemical.
- Highly resistant to petroleum based liquids, brass is commonly used in generators, transmissions and hydraulic systems. Other uses include lubricating equipment, waste oil recovery, refining and fuel processing equipment.
- A good choice for general-purpose applications, polyprolyene holds up well in acidic or alkaline liquids. Because it is FDA approved for food contact, it can also used in low temperature applications (up to 221F, 105C) such as food service steamers and proofers.
- Used in applications with temperatures not exceeding 300F (149C), PBT features good dimensional stability and has excellent resistence to a broad range of chemicals. It can be used in conjunction with brass and Buna-N for measurement of oils and fuels.
- Provides excellent buoyancy in petroleum based liquids such as diesal fuel and lubricating oils. Widely used in storage tanks of vehicles, generators, transmissions and hydraulic systems. Also suitable for dilute acids and bases, aromatic hydrocarbons and salt water.
- Kynar (PVDF)
- A high purity engineered plastic that offers resistance to harsh thermal, chemical and ultraviolet environments. It is often used in chemical and semiconductor processing at a fraction of the cost of Teflon.