Soft-Seated vs Metal-Seated Valves: How to Choose the Right Seat
Quick Answer
Soft-seated valves use a polymer such as PTFE to achieve bubble-tight shutoff at moderate temperature. Metal-seated valves use metal-to-metal contact for high temperature, abrasive, or slurry service but trade some tightness. Choose soft seats for clean, low-temperature tight shutoff and metal seats for heat, abrasion, or fire-safe duty.
Comparison
| Factor | Soft seat | Metal seat |
|---|---|---|
| Temperature | Up to about 200 degrees C | Well above 200 degrees C |
| Shutoff | Bubble-tight | Tight but not bubble-tight |
| Abrasion | Poor | Good |
| Cost | Lower | Higher |
Where Soft Seats Win
Clean gases and liquids at moderate temperature where zero leakage matters: instrument isolation, hygienic lines, and general on/off service. See the ball valve guide for typical soft-seated quarter-turn use.
Where Metal Seats Win
High temperature, thermal cycling, slurries, and coking services. Metal seats also back up soft seats in fire-safe designs described in our cryogenic and special-service guide.
Seat Material Options
- PTFE and reinforced PTFE: chemical resistance, low friction.
- RPTFE: added filler for temperature and wear.
- Metal (Stellite, 13Cr): hard-facing for erosion.
Our body and trim compatibility guide covers trim pairings in detail.
References
Seat selection follows API 598 leakage classes and manufacturer trim data. Confirm temperature limits from the current data sheet.
Frequently Asked Questions
What is a soft-seated valve?
A valve whose sealing surface is a polymer such as PTFE, giving bubble-tight shutoff at moderate temperature.
What temperature can a soft seat handle?
Most PTFE-based soft seats are limited to about 200 degrees C; reinforced grades extend this modestly.
Are metal-seated valves bubble-tight?
Typically no. Metal-to-metal seats are very tight but do not reach bubble-tight Class VI shutoff.
Which seat is better for slurry?
Metal seats, because soft seats wear quickly against abrasive particles.
Can a valve have both?
Yes. Fire-safe valves pair a soft seat with a metal backup seat so sealing continues after the soft seat burns out.