Step 1 — define the function
- Isolation (on/off): gate, ball, plug, butterfly
- Throttling / control: globe, control ball, segmented ball, butterfly
- Non-return: swing, lift, dual-plate check
- Overpressure protection: PSV / PRV (sized per API 520/521)
Step 2 — match the service
- Clean liquids / gas: ball or gate are first choice
- Slurry / particulates: knife gate, full-port ball, pinch
- High ΔP / cavitating: anti-cavitation trim globe
- Cryogenic / LNG: extended-bonnet ball or globe
- Sour / H2S service: NACE MR0175 / ISO 15156 compliant trim
Step 3 — set rating and tightness
- Pressure class per ASME B16.34 vs design P/T
- Seat leakage class per API 598 / FCI 70-2 (Class IV/V/VI)
- Fire-safe (API 607 / 6FA) where required
- Fugitive emissions (ISO 15848-1) for VOC service
Key references
- · ASME B16.34
- · API 598
- · API 6D
Use of this content
This page is a decision-support and training reference. It is not a substitute for the governing code, the project specification, or the judgement of a responsible engineer. Always validate against the current edition of the applicable standard before use on live engineering work.