Ball valves play a critical role in controlling the flow of fluid and pressure within a pipeline, but their effectiveness and safety is only as good as the seat material used. In this blog post, we are going to review the basics of five commonly used ball valve seat materials.
Ball Valves
Whether found in a petrochemical application where a leak could be environmentally devastating, or in a pharmaceutical laboratory where cleanliness and sanitation are critical, ball valve seats must be reliable and robust. A ball valve consists of the body of the valve, the body cap, the stem, the hollow ball, and the round ball valve seat.
The ball valve seat is responsible for sealing the fluid inside and uniformly distributing the seating stress. In soft seat ball valve designs, either an elastomer or polymer is used as the seal and are inserted into a metallic seat ring. This approach, as opposed to hard seat ball valves, is popular because it provides good sealing action, is lighter weight, and more cost effective.
Key Properties of Ball Valve Seat Materials
When choosing a polymer material for a ball valve seat, there are numerous factors that are involved. Key material properties include …
- Sufficient ductility to provide a reliable seal
- Dimensional stability to ensure the ball valve seat retains its shape for reliable sealing and performance
- Very low friction to keep stem torque at a minimum
- Low coefficient of thermal expansion so that the ball valve seat retains its shape when temperature changes occur
- Excellent wear resistance for a long service life
- Chemical compatibility with all media involved
In some operating environments, it is also important that ball valve seat materials exhibit these properties:
- Low moisture absorption to prevent dimensional changes in the presence of water or high humidity
- Maintain performance with repeated sterilization that can include hot water, steam, and harsh cleaning chemicals
- Good performance in the presence of sudden decompression (i.e., pressure drops over 650 psi)
Recommended Materials for Ball Valve Seats
There are several materials that work well as ball valve seats, including acetal, PEEK, PTFE, TFM, and UHMW-PE.
Acetal Ball Valve Seats
When aggressive environments are involved, Acetal (also known as Delrin) is often used. Acetal provides excellent wear resistance, is very rigid, has good toughness, and is resistant to cold flow. Although its operating temperature range is not very wide (-70°F to 180°F), it can handle pressures up to 5,000 psi. Acetal also works well in radioactive environments but should not be used with oxygen flow.
PEEK Ball Valve Seats
PEEK offers excellent chemical resistance, very low friction, self-lubrication, and is flame retardant while also possessing a wide operating temperature range (from -70°F to 550°F). It can handle very aggressive applications and works well when there is a need for hot water and steam exposure–but does not do well in the presence of sulfuric acid.
In addition, PEEK is very well adapted to nuclear applications and is available in FDA-approved grades as well as filled grades with improved wear properties and better thermal conductivity. Note that PEEK is usually chosen for ball valve seats when the operating temperature range is outside that of PTFE.
PTFE Ball Valve Seats
PTFE (also known by its trade name, Teflon) has many of the same properties as PEEK, but involves even lower friction, dry running capabilities, and more extensive chemical compatibility. Like PEEK, it is available in FDA-approved grades and can handle cryogenic temperatures down to -50°F and high temperatures up to 550°F as well as pressures up to 5,000 psi. \
Also like PEEK, PTFE can continue to perform even when repeatedly exposed to hot water and steam. Keep in mind, however, that PTFE does not perform well in the presence of fluorine or alkalies. PTFE is also very easy to clean and available in glass or carbon-reinforced grades that can provide improved wear characteristics, less propensity to cold creep, and lower thermal conductivity.
TFM Ball Valve Seats
TFM (sometimes referred to by the brand name Dyneon) is a second-generation PTFE material that combines the best properties of PTFE (low friction, chemical resistance, high-temperature performance) with better stress recovery and the ability to handle higher pressures. It is also more elastic and resilient than PTFE. The operating temperature of TFM ranges from -100°F to 450°F and it is well adapted to applications involving steam and thermal fluids.
UHMW-PE Ball Valve Seals
UHMW-PE, which stands for Ultra-High Molecular Weight Polyethylene, has a low coefficient of friction, an operating temperature ranging from -70° F to 200°F, good chemical resistance, good dimensional stability, and good abrasion resistance. In general ball valve seats made from UHMW-PE can handle pressures up to 1,500 psi and can handle low to medium levels of radiation exposure.
Conclusion
Ball valve seals are used in many different industries, including chemical processing plants, oil and gas operations, manufacturing facilities, food preparation, and even residential use. As a leak-proof means of pressure and flow control, their smooth and reliable operation is critical–which is why polymer materials work extremely well for ball valve seats. If you are in the market for a ball valve seat material, contact the experts at Advanced EMC. We can put our years of experience to work for you, helping you select the right material for your project.
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.