In a soft-seated ball valve, the seat — not the body — usually sets the limit on temperature and pressure. Two valves that look identical can have very different ratings because one has PTFE seats and the other PEEK. Here is how the common options compare, and how to choose without guessing.
Why the seat decides the rating
The ball seals against two polymer seat rings. As temperature rises, polymers soften and creep, so the pressure the seat can hold falls. Every valve datasheet therefore has a pressure–temperature chart, with one curve per seat material. The body marking (for example 1000 PSI) is the rating at ambient temperature; the chart tells you what is left at your operating temperature.
The common seat materials
| Seat | What it is | Strengths | Watch out for |
|---|---|---|---|
| PTFE | Virgin polytetrafluoroethylene | Excellent chemical resistance, low friction, low operating torque, economical | Lowest temperature and pressure capability of the group; creeps under load |
| RPTFE | Reinforced PTFE, usually glass-filled | Higher pressure and temperature capability than virgin PTFE; the common all-round choice | Slightly higher torque; filler can be a concern for some chemicals |
| CPTFE | Carbon-filled PTFE | Good wear resistance and dimensional stability | Check compatibility for oxidising media |
| PPL | High-performance filled polymer seat | Higher temperature capability than PTFE grades | Confirm against the chart for your pressure |
| PEEK | Polyether ether ketone | High strength and the highest temperature capability here; suits higher pressure | Higher torque and cost; harder seat needs a good ball finish |
How to choose
- Start from the medium. Most water, air, oil and gas service is fine with PTFE or RPTFE. RPTFE is a sensible default for stock.
- Then check temperature and pressure together. Find your operating point on the datasheet’s pressure–temperature chart. If it falls outside the PTFE/RPTFE curves, move to PPL or PEEK.
- Consider cycling and torque. Frequently operated manual valves benefit from the lower torque of PTFE-based seats. For actuated valves, harder seats may need a larger actuator.
- Remember the stem packing. The packing (often PTFE or RPTFE) must suit the same conditions as the seats.
Availability by series
| Series | Seat options |
|---|---|
| 1-piece threaded | PTFE, RPTFE |
| 2-piece threaded | PTFE, RPTFE, PPL, PEEK |
| 3-piece threaded | PTFE, RPTFE, CPTFE, PPL, PEEK |
| High-pressure 3-piece | RPTFE, PPL, PEEK |
| ANSI Class 150 flanged | PTFE, RPTFE, CPTFE, PPL, PEEK |
We do not quote one temperature limit for a whole series, because it depends on the seat, the pressure and the medium together. Send us the medium, operating temperature and pressure, and we will confirm the seat and the rating for your exact configuration.