Most ball valve seats are made of a polymer material primarily because of their elasticity, which it vital for achieving a good seal. They perform well at low pressure differentials, provide low operating torques, and usually have low coefficients of friction. Lets look at some materials that are being used for ball valve seats.
9 Significant Purchasing Options for Ball Valve Seats
One of the most popular choices for a ball valve seat material is PTFE because of its…
- low friction, chemical inertness
- FDA approval
- excellent sealing properties
Its high coefficient of expansion means that it can deform when exposed to temperature changes, and it is susceptible to cold creep. It also has a maximum lifetime radiation dose of 1×104 rads.
Another option is carbon graphite filled PTFE, which is well adapted to steam and oil industry applications. It performs better than virgin PTFE in environments with higher pressure and temperature. It has…
- good wear characteristics
- relatively low friction, and
- not as likely to cold creep.
It is not usually recommended for environments where it will be exposed to fluorine and liquid alkalis.
Glass-filled PTFE is suitable for higher pressure applications than virgin PTFE, and exhibits less cold creep. It has been found well suited to the food and pharmaceutical industry. As with carbon graphite filled PTFE, it has…
- good wear characteristics
- low friction
- more resistant to extrusion.
There are two specific drawbacks to glass filled PTFE:
- Potential abrasion of the ball from the glass fibers.
- Sensitivity to chemicals that can attack glass (e.g., hot/strong caustics or hydrofluoric acid)..
Another version would be a modified filled PTFE: It has a low coefficient of thermal expansion than virgin PTFE, making it more dimensionally stable. It works well for steam and thermal fluid applications.
PEEK is another popular choice for polymer ball valve seats, showing its strengths in high temperature and high pressure applications. However, it is not as chemically inert as PTFE (it should never be exposed to sulfuric acid) and the coefficient of friction of PEEK is higher, requiring a more stem torque. It does, however, perform very well if exposed to radiation.
Virgin PEEK works well for steam applications (remaining unaffected by continuous exposure to steam) and ultra-high vacuum applications PEEK is also resistant to radiation. It is also used regularly in the oil and gas industry where temperatures may be too high for PTFE to work well. Compared to PTFE it is more abrasion resistant. Carbon filled PEEK works at higher temperature and loads than virgin PEEK, and has been found to work well in very corrosive environments.
UHMWPE is another option for ball valve seats: it is tough, resistant to many types of corrosive materials, has low friction, and is ideal for situations where it will be exposed to abrasive media. Its usefulness in low-level radiation environments make it a good choice in the nuclear industry.
Delrin (Polyoxy-methylene) has also been used for valve seats. Unlike the other polymers, it tends to be harder and less elastic. Unlike PTFE, it is not susceptible to cold flow. It has excellent abrasion resistance, friction, wear, and strength properties. It also provides a significantly better service in radiation. However, it should not be used with oxygen flow.
Vespel is a high performance polyimide resin made by DuPont. It works well even at elevated temperatures when exposed to a wide range of chemicals, and is suitable for cryogenic applications. It performs very, very well when exposed to radiation.
Defining Your Ball Valve Seats Options:
The next time you get ready to specify a ball valve, keep in mind that you have several seat materials to choose from. Take a look at our Advanced EMC Technologies’ Ball Valve Seats and Sealing Solutions Guide.