sTEm–at-Work Puzzle #46: Valve Selection Documentation

Process technicians have the expected mechatronics skill needed to trouble shoot and repair the equipment in a process stream and knowledge of the operations of process Final Control Elements (FCE). A flow valve is a common and ubiquitous FCE in chemical processes. Often the tech has to select or identify replacement valves based on process specifications.

In this situation the Tech is reviewing that documentation with the knowledge that the actual value in service (in the pipe) is a "Decreasing Sensitivity" valve type. The other two popular valve types are the Increasing Sensitivity valve type and the Linear Response type.  The Tech is checking to see if the value in the process is labeled correctly. The tag on the valve indicates it is Valve 34-a. The technician knows that the valve is supposed to be "Decreasing Sensitivity" type and understands that for "Decreasing Sensitivity valves” the change in flow rate compared to the change in the valve position (stem motion) decreases as the valve becomes closer to being wide open. The tech also knows that Valve 34-b is a Linear Response type.  In addition, the Tech knows how to read the valve performance plots shown in the graph below.

The Tech decided that the valve installed in the flow stream is correctly labeled as Valve 34-a.
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