Flexible Wedge vs Solid Wedge Gate Valves for Steam
Technical guide · Supreme Valves India · Updated 2026-10-28
Direct answer: On steam and thermally cycled lines, specify a flexible wedge API 600 gate so seating faces can tolerate body expansion without binding. Use a solid wedge for steady, cooler utility service. Write the wedge type on the RFQ — do not leave it to chance.
Comparison
| Flexible wedge | Solid wedge | |
|---|---|---|
| Thermal cycling | Preferred | Risk of binding |
| Steam mains / headers | Common on BOQs | Avoid unless approved |
| Ambient water | Optional | Typical |
| BOQ phrase | FLEXIBLE WEDGE | SOLID WEDGE |
Archive language
WCB Class 150/600 RFQs often include “FULL PORT, FLEXIBLE WEDGE, API TRIM #8”. That combination is deliberate for process and steam isolation.
RFQ checklist
- Flexible or solid wedge
- Trim / Stellite
- OS&Y bolted bonnet
- IBR if boiler code applies
See WCB Class 150 gate RFQ and Class 600 gate RFQ.
Frequently asked questions
What is a flexible wedge?
A gate wedge with a controlled flexure feature so the seating faces can adjust slightly as the valve body expands or contracts with temperature — reducing thermal binding on steam lines.
When is a solid wedge OK?
Ambient or mild utility service with little thermal cycling. Many water and low-temperature hydrocarbon gates use solid wedges successfully.
Do forged Class 800 gates use flexible wedges?
Small forged API 602 gates often use solid wedges by design. Follow the forged valve datasheet; do not assume cast API 600 flexible-wedge language applies.