Choosing Materials for Process Applications: Plastic Valves & Instrumentation
Engineers will often specify brass or stainless steel valves and instrumentation into an application because they are familiar with the material, even if it is not the most appropriate material for the application. This article will assist readers in understanding the important factors to consider when specifying the right material for an application. The article will then identify situation in which plastic might be the most appropriate material to use, and will give examples of different polymers being used within application.
Choosing the correct material for an Application
The same rules apply for flow control with plastic valves and plastic instrumentation, as they do with metals and ceramics. All materials have to be judged by various features defined by the applications.
Important characteristics when choosing Valve Materials
- Temperature: The temperatures of fluid and ambient have to be considered not only for the main housing material, but also for the used seals. Additionally that has to be considered in combination with the fluids. Chemical properties of some fluids vary with temperature and might require different materials to be used even throughout one system.
- Pressure: The pressure is another key factor for choosing materials. Also, the combination of the pressure rating with the temperatures involved in the application can result in some process limitations.
- Fluid: The type of fluid being controlled must be considered, media can affect the temperature and the pressure of the flow.
Other important characteristics for choosing valve materials:
- Mechanical stresses
- The surrounding atmosphere
- Safety or hygienic regulations
These features might all have an impact on the selection of the right material.
Which Plastics to Choose & Why?
The most common plastic materials used in industrial applications are as follows:
PVC-U: The standard material for industrial applications and in the field of water treatment due to its generally acceptable technical properties in combination with low cost.
PP: For more demanding industrial applications often PP is used due to its higher temperature and pressure resistance in combination with better chemical properties.
PVDF: The highest rated standard material for demanding applications, e.g. in the food, pharmaceutical or chemical industry or when higher temperatures need to be handled.
Therefore, plastic valves and instrumentation can offer real-value to applications, especially in aggressive, hygienic or aseptic applications where metallic equivalents can dramatically increase the cost of the solution.