General engineering orientation to help you specify and enquire with confidence. Guidance only — selection, configuration and scope are confirmed against your project specification at quotation.
Valve ratings basics
Industrial valves are rated by the same designation systems as flanges: ASME pressure classes for imperial-designated valves and PN designations for metric valves. The rating group, body material and service temperature together set the allowable working pressure.
Shell rating and seat rating
A valve carries two distinct ratings. The shell (body) rating is the pressure envelope of the pressure-retaining body at temperature. The seat rating is the differential pressure the closure member can shut off against, which for soft-seated designs is often lower than the shell rating and falls further at elevated temperature. Both must suit the duty.
Temperature effects
Ratings are always stated at a reference temperature and de-rate as service temperature rises. Soft seat and seal materials introduce their own temperature limits independent of the body rating. State the full service temperature range at enquiry, not only the operating point.
What to confirm at enquiry
- Class or PN designation and governing standard
- Service pressure and temperature range
- Shut-off (differential) pressure requirement
- Body and trim materials
- Seat type — metal or soft-seated
These are buyer-input prompts only and are confirmed against your project specification. Send them with your enquiry for engineering review.