Valve performance is the key to process variability reduction. In fact, up to 20% of process variability can be attributed to poor control valve performance. Although substantially improved in the last decade, valve performance still remains a frequent source of process variability due to:

• Variable deadtime
• Actuator coupling backlash not measured by a position sensor
• Friction caused by an undersized actuator

Manual control valves may also become problematic if, for example,  it is assumed that a control valve’s position is constant when it is actually moving on its own – a difficult problem to troubleshoot.