These problems are characterized by:
Frequent maintenance needs; for example, a user will say that ‘we have to rebuild this valve every shutdown.’ The maintenance cycle has been done so many times it has become the norm.
Valves that work perfectly after rebuild maintenance but in a relatively short period become a headache again, performing poorly and unreliably.
Cause concerns during startup and shutdown as to whether they will get through the transient. However once the system is at full load the problems go away.
Valves for which the control system has to be put in manual operation because trips occur when the system is in automatic.
Valve bypass loops are put into service during startup and shutdown transients to allow stable operation of the main valve.
Extensive perturbations to the system when transferring from a parallel startup valve. The upset can cause trips or lifting of relief and safety valves. The corrective procedures become the standard to work around the problem.
These problem valves exist because of:
1 Misapplication of the valve design selected.
2 Over or under sizing the valve for the process need.
3 Poorly specified requirements to the supplier