What is valve rangeability and why does it matter?

Rangeability is the ratio of maximum controllable flow to minimum controllable flow, expressed as a ratio (e.g., 50:1). A valve with 50:1 rangeability can control flow from 100% down to 2% of maximum. Factors affecting rangeability: valve type (globe typically 50:1, ball 100:1), trim design, and process conditions. Why it matters: wide rangeability allows single valve to handle large flow variations; insufficient rangeability requires multiple valves or valve selection compromise. Installed rangeability is typically lower than inherent due to process pressure variations.