Polymer Ball Valve Seats
The ball valve seat aids in distributing the seating stress uniformly and is usually soft enough to conform to the shape of the ball so that a solid seal is achieved. Ball valve seats involve a collection of material requirements to work correctly. Essential properties include:
- low friction
- sufficient ductility to provide a reliable seal
- good stress recovery
- dimensional stability
- excellent wear resistance
High-Performance Ball Valve Seat Materials
However, when it comes to critical applications in aggressive environments, ball valve seat materials also need to be resistant to chemical attack, have stable properties even at extreme temperatures (which could include cryogenic or high temperatures), low water absorption, and a very low coefficient of thermal expansion. For applications that require sterilization (e.g., food and drug), ball valve seats need to be able to handle extended exposure to hot water, steam, or potentially caustic cleaning compounds.
Typical polymer materials used for ball valve seats include PTFE, PEEK, TFM, nylon, acetal, and UHMW PE and others. However, not all materials are suitable for ball valve seats that have to function in an aggressive environment reliably.
PTFE Ball Valve Seats
As a ball valve seat material, PTFE often rises to the top of the list because of its incredibly low friction and excellent chemical compatibility across a wide range of chemical types. It is available in several FDA-approved grades and is considered non-contaminating. PTFE can handle cryogenic temperatures, and its kryptonite is exposure to fluorine and liquid alkalis.
Depending on the types of additives used, PTFE can achieve performance in temperatures up to 550°F and survive even with repeated exposure to steam and hot water.
PEEK Ball Valve Seats
PEEK has chemical resistance and low friction almost on the same order as PTFE, but can handle slightly higher temperatures ranging from -70°F to 550°F. This material is exceptionally well adapted to nuclear applications and those involving high temperatures and extreme loadings. PEEK is also quite flame retardant and is suitable for hot water and steam exposure.
TFM Ball Valve Seats
TFM is a specially formulated second-generation variant of PTFE. It is known for its low friction, good performance in high temperatures, and chemical resistance. TFM offers even better stress recovery than PTFE and has a denser molecular structure. Its working temperature range is -100°F to 450°F.
Acetal Ball Valve Seats
Another common choice for ball valve seats in aggressive environments is acetal (sometimes known by one of its trademarked names, Delrin). Its temperature range is more limited at -70°F to 180°F, but it offers outstanding wear resistance and can handle pressure up to 5 ksi. It is a very rigid material with good toughness and dimensional stability and is resistant to cold flow.