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Technical Articles
January 19, 2016


Other materials found in plastic valves & controls

While valve bodies are generally either thermoplastics or fluoroplastics, and seals are generally thermoplastic elastomers, many plastic valves use metals in some fashion. In a properly designed valve, these metals have no contact with process media and minimal external exposure. Valve bodies that are not threaded together require a fastener of some type; the best combination of strength and resistance is a stainless steel fastener. In many cases valve bodies are threaded together to eliminate the need for external fasteners, but in certain types of valves the fastener improves the design via added strength and rigidity. Pressure valves, for instance, tend not to perform as well if the body is threaded from two separate parts (note that Plast-O-Matic’s pressure valves without fasteners have a unibody design and use separate parts specifically for threading).

Springs are used in fail-safe and automatic pressure valves (relief valves, pressure regulators, etc.) and are generally some type of steel; often stainless steel or other steel, determined by the spring rate and other specific properties required by the valve design and function.
Solenoid Valves use many other materials. In a good plastic valve design, these materials are intentionally isolated from any contact with liquid (unless specified in the design) but can have exposure to atmosphere. Solenoid core tubes frequently include stainless steel, stainless steel with some ferrous properties, sometimes copper, silver, and other metal parts. Solenoid coils are generally some type of polyester and another plastic material. Some solenoid coils have metal housings. It is important to check the specifications for each valve to ensure that materials are compatible with your process and/or environment.

Acrylics are used in valve and piping components design where visual verification is desired. Sight glasses and level indicators use acrylic and many shutoff valves also use acrylic. It offers excellent abrasion resistance, and excellent optical quality. It also resists UV light.

Epoxy and other potting materials are used in certain valves and system controls to isolate switches, sensors, etc. These are often limited to atmospheric exposure, but in some products, epoxies are exposed to liquid. They generally perform as well as typical piping polymers, although some epoxies are susceptible to chromic acids, high concentrations of nitric acid, and a number of plating solutions such as copper sulfate bath, nickel plating bath, fluoride baths, and others. Flow Switches have wetted Epocap® brand epoxy and compatibility can be checked by clicking here and referring to the right hand column titled “epoxy.” As with any material, controlled testing under your application parameters is the only way to truly determine chemical compatibility.