What are the design considerations for emergency isolation valves (EIV)?

Emergency isolation valve design: valve type selection (ball for tight shutoff, gate for full bore, butterfly for large sizes), actuator sizing (fast closing per ESD requirements, often <10 seconds), fail-safe action (spring-return pneumatic, hydraulic with accumulators), fire-safe design (API 607 or API 6FA), seat leakage class (Class V or VI for critical isolation), position feedback (limit switches at both positions), partial stroke testing capability, manual override (accessible handwheel), and fire-safe accessories (fusible links, fire-tested solenoids). Document: safety manual with failure rate data, proof test procedures, and stroke time requirements. Consider velocity effects, water hammer, and process compatibility.