Specifying the correct solenoid valve material and seals for your chemical application
Burkert Fluid Control Systems provide us with the important considerations for selecting the correct solenoid valve for your application, especially when chemical resistance is important. An overview of the most common valve body materials and solenoid valve seals is also provided.
Which type of Solenoid Valve?
A correct solenoid valve to use in a brewery application can be very different to the correct solenoid valve to be installed in a pharmaceutical application. To ensure a long and trouble-free service from your solenoid valves, it is essential that the correct valve is chosen for the correct application – and that generally means ensuring the correct valve materials are specified in the design process.
Specifically, an engineer must consider the chemical resistance properties of the solenoid valve housing and gasket materials in relation to the substances in which the valve is expected to control.
Specifying the correct solenoid valve for your application
So how can engineers navigate through the minefield of choices and contradictions in valve material selection?
Product Manager for Solenoid Valves, Michael Hannig from Burkert Fluid Control Systems has provided us with an overview of the important considerations when selecting solenoid valve components for applications with high chemical resistance.
The type of solenoid valve most appropriate for each application is governed by a number of factors. Many of the solenoid valve components, such as the plunger, return spring and seal are all exposed to the media and therefore information on the chemical compounds, temperature and pressure are all necessary to make an informed material selection. However, regarding solenoid valve design the general rule-of-thumb is;
- Plunger-type direct acting solenoid valves are best suited to neutral and clean fluids.
- Pivoted armature solenoid valves employ a media-separating membrane and are therefore suitable for controlling corrosive, contaminated or aggressive fluids.
If the application involves liquid food products, it is important to ensure the plastics and elastomers in the solenoid valves conform to the applicable food and hygiene regulations.
Another factor to consider is; does the process require a cleaning cycle to be performed in between production processes? If the answer is yes, then this process itself can lead to material degradation in the valves. It is important to consider data for this procedure in the valve design and selection process.
Other factors to consider which will all have a bearing on the performance of the solenoid valve include mechanical loading, cryogenic temperatures and chemical concentration of process media.
What about options for solenoid valve sealing?
There is an extensive range of options for valve sealing and separating membranes. Decision criterion includes the combination of chemical compound, temperature, pressure and cost. These different options and have different benefits and drawbacks.
Selecting the correct material for valve seals and valve bodies can be a minefield. Michael Hannig provides us with a brief overview of the most common compounds used for valve sealing and separating membranes below, highlighting the benefits and the pitfalls of each one.
Common materials used for valve body & seals
More information on selecting the correct material for your application can be found in this useful & detailed pdf. Here you will find Burkert’s chemical resistance chart and selection guide for solenoid valves – a detailed and useful resource to help in the solenoid valve design and selection process.
PTFE (Polytrafluoroethylene) – suited to severe chemical resistance applications
PTFE diaphragms and flange gaskets are used in the most severe chemical resistance applications. PTFE is almost totally insoluble, has a high temperature resistance and is chemically inert.
EPDM (Ethylene Propylene Terpolymer) – suited to acids, alkalis and salts
EPDM is the most standard seat material for many valves, being the most economical choice. EPDM has an excellent resistance to acids, alkalis, salts up to 90°C.
EPDM is not suitable for use with oils, petrochemicals and concentrated acids.
NBR (Nitrile Rubber) – suited to oil and petroleum applications.
NBR does have a high chemical resistance to oils and petroleum and has an excellent abrasion resistance. However, NBR is weak on oxidising media such as acids.
NBR is a more cost-effective compound than FKM and FFKM
FKM/FFKM (Fluorinated Elastomer/Perfluoro Elastomer) – suited to high temperatures
FKM/FFKM provide more chemical and temperature resistance compared to nitrile (NBR) and neoprene elastomers, some grades of FFKM can perform continuously at temperatures above 200°C. FKM/FFKM are therefore generally more expensive options.
PPS (Polyphenyl Sulphide) – suited to temperatures above 200°C
PPS can perform above 200°C and is resistant to acids and alkalis as well as abrasion. PPS can be selected as a valve body material and is a high performance thermoplastic used in many engineering applications.
PVDF (Polyvinylidene Fluoride) – suitable for valve bodies in acid & solvent applications
PVDF is an extremely flexible product which can be injected, moulded and welded and is therefore suited to the manufacture of valve bodies. It is resistant to solvents, acids and bases but is not suitable for application where high temperature resistance is required.
PEEK (Polyether Ether Ketone) – provides superior quality as a valve body material
PEEK is generally more expensive as it has excellent mechanical and chemical properties and it therefore provides superior quality as a valve body material.
However, PEEK is more susceptible to high concentrations of sulphuric and nitric acid.
To ask Michael Hannig a technical question directly, please visit our Solution Centre where technical experts are on-hand to answer your questions. Alternatively, you can contact Burkert directly by clicking here to visit their PIF Profile.
Has this guide been helpful in providing you with an overview on solenoid valve material selection? Are there any more widely used compounds you would like to know about?
We would love to hear your feedback and additions below.