Valve selection for chemical applicationsTim Cannon | June 07, 2022
When working with chemicals, there are a lot of considerations that must be made when selecting the appropriate equipment to use. The specific factors that can affect valve compatibility include temperature, pressure, the materials that the valve itself is made of, the material of the seals, the types of connections on the valve and, lastly, how the valve will be controlled. When searching for the right valve to use, it can quickly become overwhelming. We will highlight the main things that need to be considered when looking for the right valve for any chemical application.
One of the most important things to consider is the materials of the valve itself. This includes the body of the valve as well as the trim materials. It is very critical to take a look at the fluid that will be going through the valves and determine what materials are compatible. Depending on the specific chemicals that are being used, there may be several options or only a single good option for valve materials.
Most valves come in a wide variety of materials. These generally include stainless steel, brass, bronze, iron, carbon steel and even plastic. Depending on the application's corrosion requirements, pressures, and temperatures certain materials will do better than others. Even for materials such as iron that do not have great corrosion resistance on their own, a coating can be applied that will improve its corrosion resistance. As such, there are lots of different options available to ensure that anyone can find the perfect match for their chemical process.
Temperature, pressure and corrosion
As previously mentioned, it is important to be aware of the temperature, pressure and corrosion requirements of a chemical process application. Even in a single material, there are often several different valves that are capable of withstanding various temperature and pressure ranges. As such, it is important to know and verify what kind of temperatures and pressures to expect in the fluids in order to select the right valve for the application.
Selecting a valve that meets the corrosion, pressure and temperature requirements for a given chemical process is critically important. Otherwise, a chemical process could experience contaminated fluid media, leaks and even failure of the valve itself. If a specific chemical is operating at high temperatures or pressures or is acidic or harmful to humans in any way, this can pose a huge safety risk to those who may be working near the plumbing.
It is also important that the corrosive effects that a specific chemical can have on materials is adequately understood. Without this knowledge, it can be very hard to select the right valve. Choosing a bad valve material can lead to rust, corrosion, contamination of the process fluid, leaks in the valve and even failure of the valve. That is why it is important that there is a good understanding of what materials are compatible with any used chemicals.
Next, it is very important that a compatible seal material for use in a valve is selected. The selection of the seal material is just as important as the material selection for the valve body itself. Any given valve will generally come with several different options for seals. Generally, the types of seals are either elastomers or plastics. The elastomers will usually provide the best sealing, but plastics can be necessary when working with harsh and corrosive chemicals.
Apart from just fluid compatibility, it is also important to take into consideration pressure and temperature as well. Different seal materials will have different capabilities. Lastly, it is important to consider the cost of the different seals as well. It is generally a good idea to have spare components on hand so that a bad valve can be rebuilt at a moment's notice when it wears out. This will require having extra seals available to be used.
Considering the valve connections beforehand is critical to setting up a new process or adding a new valve into an existing process. There are many different ways that a valve can be connected to a fluid process. These often include threaded connections, welded connections and flanged connections. Threaded connections could include NPT, SAE, Swagelok, Face Seal and JIC fittings. For both welded and flanged connections, there are several different styles as well.
Threaded connections are a great choice when cost is the main driving factor. These are generally the cheapest style of connection but can wear out with time. The threads themselves can get damaged or stripped and the seals can start to fail with time. Welded connections provide leak-tight fluid paths but can be very frustrating if they need to be removed from the fluid path as it will require cutting the piping or tubing. Flanged ends are generally the most expensive connection but they are incredibly simple to add and remove when needed.
Lastly, it is important to consider how the valve will be operated. These could be hand valves of many different styles or control valves. If control valves are being used, it is important to verify that the appropriate methods are available in order to control the valve (compressed air, high pressure gas, electricity or hydraulics). In addition, the level of automation required can decide what type of control method is acceptable. This is generally the easiest valve selection criteria to navigate.
Each process is different
In the world of chemical processes, each process is different. Depending on any given application-specific requirements the requirements for valving will also change. By taking into consideration the things that have been discussed here, the correct valve for any chemical process can be selected. This ensures a safe, reliable and maintainable chemical process. These should be requirements for every single chemical process as the purity of the chemical and the safety of those working around it are of paramount importance.
About the Author
Tim has a bachelor's degree in mechanical engineering from BYU-Idaho. He currently works as a control systems engineer for Ram Aviation, Space and Defense, where he designs pneumatic and hydraulic valves, and as a LabVIEW consultant for EZtech-stop. He has worked for Hyundai as a Thermal Systems Engineer and the Idaho National Laboratory as a Nuclear Systems Engineer in the past.