Under and Over-Capacity Control Valve Pose Poor Controllability

Instrumentation engineering root cause analysis (RCA) of under and over-capacity control valves pose poor controllability.

Note: This root cause analysis (RCA) is from real-time scenarios that happened in industries during the tenure of two or three decades ago. These articles will help you to improve your troubleshooting skills and knowledge.

Under and Over Capacity Control Valve

Two control valves posed problems (P) and the Author RCA solutions (S) are as under:

Problem:

Poor boiler drum level control because of just 15% open LCV 301

Solution:

Obviously poor controllability oversized control valve (CV).

Re-calibrate the 30-mm valve travel VP (valve positioner) for 20 mm travel and fix a new 20 mm marks scale.

Problem:

Even with exit PCV 213 full open, First Flash Separator pressure was > SP

Solution:

Obviously, control valve (CV) opening is insufficient;

Re-calibrate the valve positioner (VP) from 35 mm to 55 mm and fit a 55 mm marking scale

Benefits of the Solution

Excellent control, saved new valves purchase costs, and commissioning proceeding on schedule.

Author: S. Raghava Chari

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