For trunnion-mounted ball valve, there is a metal seat ring and a soft seat insert to ensure the sealing performance of seat.

The seat inserts are element mounted inside a metal seat ring and perform the same sealing functions as seat ring.

There are mainly two types of seat insert materials, elastomeric and thermoplastic. Elastomeric seat insert is softer to achieve zero leakage of ball valve. While thermoplastic seat insert is harder to bear scratches, erosions and wider range of temperature and pressure rating.

Let’s take a look at the details of these seat insert materials.

-PTFE is mostly often used for a wide range of temperature and fluids, but not suitable for high pressure application.

-Nylon can bear higher pressure than PTFE, but has a limitation on temperature range.

-Devlon has similar strength to Nylon, but it can be used under a wider range of temperature.

-PEEK is recommended for higher temperature (up to 260 deg.C), but it is much harder than other soft material.

-Kel-F is especially recommended for cryogenic service.