Valve Position Indication:

Operators need indication of the position of certain valves to allow knowledgeable operation of the plant. For such valves, remote valve position indication is given in the form of position lights which denotes if valves are open or closed. Remote valve position indication circuits use a position detector in which senses stem and disk position or actuator position. A single type of position detector is the mechanical limit switch that is physically operated through valve movement.

Another category is magnetic switches or transformers in which sense movement of their magnetic cores that are physically operated through valve movement.

Local valve position indication refers to a few visually discernable features of the valve which indicates valve position. Rising stem valve position is denoted through the stem position. Nonrising stem valves sometimes have little mechanical pointers which are operated through the valve actuator concurrently along with valve operation. Power actuated valves classically have a mechanical pointer which provides local valve position indication. Alternatively, a few valves do not have any characteristics for position indication.