Control valve selection plays a crucial role in optimizing control loop performance, and engineers must consider factors beyond just cost, leakage class and pressure drop.
As explored in a Control article, valves designed for on-off service may seem attractive for throttling applications due to their lower cost and tight shutoff, but their inherent limitations in actuators and mechanical assemblies can severely degrade control performance.
Nonlinearities in valve response—such as deadtime, lost motion, resolution limits and travel gain inconsistencies—can introduce significant challenges, particularly in high-precision processes. To address these concerns, Annex A of the ISA-TR75.25.02-2000 (R2023) report provides insights into the impact of these nonlinearities and offers guidance on specifications and tests to ensure that control valves meet dynamic performance requirements.
Response time, particularly the time to reach 86% of the final valve response (T86), is critical for fast-acting loops such as pressure control and compressor surge applications. Slow responses, especially for small signal reversals, can lead to instability and limit cycles in the control loop.
To learn more about control valves, read the full article from Control, an Automation World partner publication.
