Power-plant steam is the duty that punishes soft seats and punishes guesswork. Main-steam and boiler-side isolation runs at temperatures where elastomers are long past their ceilings, where the wedge-gate-versus-parallel-slide question is real, and where the pressure class comes out of a table, not a rule of thumb.
The typical duties below are the ones the selector was built around. Run your own numbers in the tool — the box shows what it answers for the reference duty, computed by the same engine at the moment this page was built.
Typical duties
| Main steam isolation | Steam · up to ~100 bar · 480–540 °C · DN100–300 |
|---|---|
| Feedwater and boiler auxiliaries | Water/steam · 25–60 bar · 120–260 °C · DN50–200 |
| Steam distribution and drains | Steam · 10–40 bar · 180–300 °C · DN25–100 |
90 bar · 480 °C · DN150 on Steam (saturated / superheated) (steam): Ball Valve (floating / trunnion-mounted) · body 1.25Cr-0.5Mo alloy steel (ASTM A217 WC6).
bubble-tight quarter-turn isolation is the modern default for this duty
/* r11 P3-6 (user-approved): the duty-specific caution (e.g. class utilisation) belongs ON the page, not only in the unlocked report — the last boilerplate line stays report-only */Watch: Pressure class NOT computed for 1.25Cr-0.5Mo alloy steel (ASTM A217 WC6): our B16.34 tables cover WCB and CF8M. Assign the class per the table for this body's group and confirm with the manufacturer — we decline to print an invented number.
What to watch
- Above 250 °C the wedge-gate seizure risk on steam is a real constraint, not a footnote — the engine's notes say when it applies.
- The seat ceiling upgrades rather than eliminates: a soft seat past its limit becomes a metal seat with the reason printed.
- Pressure class is read from the ASME B16.34 table for the chosen body material at your temperature.
Where this connects on this site
- Steam as a medium — the material picture
- Gate valves — the steam-isolation workhorse
- Globe valves — when the duty is regulation, not isolation
- Soft-Seated vs Metal-Seated Valves: Where the Temperature Line Is
Boundary rule: this page states single-point conclusions from the site's knowledge base — no supplier names, no matrices. The full 40-medium library lives in the selector.