Valve seat material selection involves more than chemical compatibility. Chemical compatibility tells you whether a material can survive contact with the media; it does not necessarily tell you whether it will perform reliably in the actual valve application.
Temperature, pressure, cycling frequency, abrasion, steam, cleaning chemicals, and other operating conditions can affect how a seat or seal performs over time. The material may be chemically compatible with the process fluid and still experience premature wear, deformation, leakage, or failure under actual operating conditions.
Assured Automation’s Butterfly Valve Seat Selection Guide provides a useful starting point for comparing common seat materials such as EPDM, Buna-N, PTFE, RPTFE, and Viton. But selecting the right material requires looking beyond compatibility charts and considering the valve’s complete operating environment.
That evaluation can also affect valve torque and, ultimately, proper actuator sizing.
Chemical Compatibility Is Only the Starting Point
Chemical compatibility should always be part of valve seat material selection, but it should not be the only criterion.
Compatibility charts help determine whether a material is generally resistant to a particular chemical. However, they usually cannot account for every condition the valve will experience in service.
Concentration matters. So does exposure time. A material that performs well in intermittent contact may behave differently under continuous exposure. Contaminants or additives in the process fluid can also change how a seat or seal performs.
Operating conditions can further alter material behavior. Higher temperatures may accelerate chemical attack or soften some materials. Repeated pressure changes can increase mechanical stress. Cleaning solutions, steam, or flush fluids may expose the valve to chemicals that are completely different from the normal process media.
That is why material selection should begin with chemical compatibility, then expand to the full operating conditions the valve will encounter.
Evaluate Temperature and Pressure Together
Evaluate temperature and pressure together when selecting valve seat and seal materials.
A material may be rated for a relatively high temperature under one set of pressure conditions, but that does not mean it can handle maximum temperature and maximum pressure at the same time. As temperature rises, some elastomers and polymers soften, lose strength, or become more susceptible to deformation. That can affect sealing performance and shorten service life.
The reverse is also important. Higher differential pressure can increase the mechanical load on the seat and increase the torque required to operate the valve. Add elevated temperature, and the demands on the material become greater.
This is why engineers should look at the manufacturer’s pressure-temperature ratings rather than relying on a single maximum temperature or pressure value.
For example, Assured Automation’s ST Series resilient-seated butterfly valves are available with either EPDM or Buna-N seats. The allowable temperature range differs by seat material, and the valve’s published pressure ratings also vary by size. Consider those specifications together for the actual application.
Engineers should also consider conditions outside normal production. Startup, shutdown, process upsets, hot flushing, and other temporary conditions may expose the valve to higher temperatures or pressure changes than it sees during steady operation.
The goal is to select a seat or seal material that performs reliably across the valve’s full operating range—not just under normal process conditions.
Consider Cycling, Friction, and Seat Wear
How often a valve operates can matter as much as what flows through it.
A valve that opens or closes only a few times a month places very different demands on its seats and seals than one that cycles hundreds or thousands of times. Each cycle creates friction between moving and sealing surfaces. Over time, repeated movement can cause wear, compression, deformation, or loss of sealing effectiveness.
Long periods in one position can create other problems. Some soft-seat materials may take a compression set or gradually deform under sustained load. Deposits around the ball, disc, or seat can also increase resistance when the valve finally moves.
These conditions affect more than seat life. Increased friction can raise the breakaway torque required to move the valve from its resting position. That becomes especially important with automated valves because the actuator must provide enough torque to overcome the actual operating resistance.
Cycle speed also matters because opening or closing a valve too quickly can create additional stresses in the system. For more on that, see “How Fast Should an Automated Valve Open or Close?”.
For frequently cycled applications, engineers should evaluate the seat material for both chemical resistance and its expected mechanical performance over the required service life.
Abrasion and Solids Change the Material Requirements
Chemical compatibility does not account for what suspended solids can do mechanically to a valve seat.
Sand, scale, metal particles, crystallized material, powders, and other solids can become trapped between sealing surfaces or pass across them during operation. Over time, these particles can scratch, cut, or wear the seat and interfere with tight shutoff.
The severity of the problem depends on more than the seat material. Particle size and concentration, flow velocity, differential pressure, valve design, and cycle frequency can all affect wear.
This is especially important in slurry service. A soft seat may offer excellent chemical resistance to the carrier fluid but still experience premature wear from the solids moving through the valve. In these applications, engineers must consider both the seat material’s mechanical properties and how the valve design handles solids.
For example, Assured Automation’s V200/300 Series V-Port Ball Valves are designed for general and slurry applications and are available with TFM or 50/50 PTFE/stainless-steel seats. The V-port design also provides a non-clogging flow path, making the valve design itself part of the material-selection decision.
When abrasion is a concern, the question is not simply, “Will this material resist the chemical?” It is also, “Will it maintain an effective seal after repeated exposure to the physical characteristics of the media?”
Steam, CIP, and Cleaning Chemicals are Part of the Process
The process fluid is not always the most demanding media a valve will encounter.
In food, beverage, pharmaceutical, and other sanitary applications, valves may also be exposed to hot water, steam, caustic cleaners, acids, sanitizers, or other fluids during clean-in-place (CIP) and steam-in-place (SIP) cycles. Include these conditions when selecting seat and seal materials.
A material that is compatible with the product being processed may react differently to a concentrated cleaning solution or repeated exposure to elevated temperatures. The frequency and duration of cleaning cycles also matter because repeated thermal and chemical exposure can affect material properties over time.
This makes it important to evaluate every fluid and temperature condition the valve will see, not just normal production conditions.
Assured Automation’s BFY Series sanitary butterfly valves are available with EPDM, Viton®, or silicone seats and seals. The valve is designed for sanitary applications, but the appropriate seat material still depends on the specific process media, cleaning chemicals, temperatures, and operating requirements.
For systems that use CIP or SIP, seat and seal selection should therefore be based on the entire production and cleaning cycle, not the process fluid alone.
Seat Material Can Affect Valve Torque and Actuator Sizing
Seat material can also affect the amount of torque required to operate a valve.
Different materials create different levels of friction against the ball or disc. Reinforced or filled PTFE seats, for example, may require more operating torque than standard PTFE. Differential pressure, temperature, deposits, dry gas, viscous fluids, and abrasive media can further increase torque requirements.
Assured Automation’s published torque data for its 36 Series stainless steel ball valves illustrates the point. Its actuator-sizing guidance calls for increasing valve torque by 15% with RPTFE seats and by 25% with certain carbon-filled or stainless-steel-filled PTFE seats. It also recommends higher torque allowances for dry gas and for viscous or abrasive media.
That matters when automating the valve. An actuator selected only from a nominal valve torque value may not provide adequate torque under actual service conditions.
Assured Automation’s C Series pneumatic actuators, for example, are available in multiple sizes and torque outputs for quarter-turn ball and butterfly valves. Proper sizing requires matching actuator output to the valve’s required torque under expected operating conditions, with an appropriate safety margin.
Seat and seal selection, valve torque, and actuator sizing should therefore be treated as related engineering decisions rather than separate specifications.
Select Valve Seat and Seal Materials for the Full Duty Cycle
Base valve seat material selection on the full duty cycle, not a single compatibility rating.
Before specifying a material, engineers should consider:
- Process media and concentration
- Normal and maximum temperature
- Operating and differential pressure
- Cycling frequency
- Abrasive solids or slurry
- Steam, CIP, and cleaning chemicals
- Required shutoff performance
- Expected service life
- Valve torque and actuator sizing
Some applications may place relatively little stress on the seat during normal production but expose it to much harsher conditions during cleaning, startup, shutdown, or infrequent operation. Others may involve chemically benign media but introduce significant mechanical wear from high cycling rates or abrasive solids.
Looking at the entire operating environment helps reduce the risk of premature leakage, excessive torque, shortened seat life, and an incorrectly sized actuator.
Need Help Selecting the Right Valve Seat or Seal Material?
Chemical compatibility is an important starting point, but reliable valve performance depends on much more.
If you are selecting an automated valve for a demanding application, contact Assured Automation with your media, temperature, pressure, cycling, cleaning, and other operating requirements.
We can help you evaluate the application, identify an appropriate valve and seat or seal material, and properly size the actuator for the expected operating conditions.
Talk to one of our valve automation experts.
Vice President of Sales