• Instrumental

Instrument Valves

Process control engineers treat final control elements in the same way they treat measurement devices - with absolute indifference.  To most of them, a valve is a valve is a valve.  It's job is to open and close according to what the controller tells them and they do just that.  The problem is, in a shocking number of cases, they don't.

Control valves and dampers, being mechanical devices are subjected to a lot of mechanical issues like wear and tear, deterioration with time.  Measurement devices these days are very robust and most would not deteriorate drastically with time.  When they fail, they just go.  The controller running inside the modern distributed control system (DCS) is even more reliable with a hot standby ready to take over in case of failure.  The same cannot be said about final control elements.  Therefore the weakest link in the process control loop is frequently the final control element.

The problems of control valves usually manifest themselves as stiction, deadband and hysteresis

Specification Content