Check Valves for Oil & Gas

API 594 covers wafer and wafer-lug check valves — compact, face-to-face short design that fits between standard flanges, primarily for process plant and general industrial service. API 6D specifically governs pipeline check valves — longer body, full-bore designs for oil and gas transmission and distribution systems. API 6D check valves have more stringent testing (extended shell test duration, seat leakage Class A with zero measured leakage for gas service), and are required on pipelines covered by DOT/PHMSA regulations in the USA and equivalent regulators elsewhere. For upstream production and process plant: API 594 or API 6D (either is acceptable depending on client specification). For custody transfer and mainline transmission: API 6D is mandatory.

Tilting disc check valves are preferred over swing checks in three scenarios: (1) Water hammer prevention — the tilting disc geometry closes faster than a full-bore swing check because the disc centre of gravity is ahead of the pivot axis, providing inherent closing torque; (2) High-pressure oil and gas service where slam damage to the seat is unacceptable — the controlled disc tilt provides soft seating; (3) Vertical pipeline installation — swing checks require near-horizontal flow to stay open; tilting disc designs work in vertical upward flow because the disc tilts with the flow. Standard swing checks remain preferred for low-pressure, horizontal pipelines in water and general service where cost is the primary driver.

Cracking pressure (minimum forward differential to open the disc) varies by application: Pipeline mainline check valves: 0.05–0.1 bar cracking pressure to open reliably at low flow; Pump discharge: 0.1–0.3 bar cracking; Compressor discharge (high-pressure gas): 0.5–2 bar acceptable — the compressor will always produce enough differential; Flare header service: specify 0.01–0.05 bar cracking pressure — flare headers operate at near-atmospheric pressure; for very low-cracking duty, use flap check valves with lightweight discs and minimal or no springs. Vajra's check valve datasheets state cracking pressure per design; request specific cracking pressure as a purchase specification if it is critical to your system design.