Lecture Notes 9
Lecture 9 - Process Equipment and Valve Design
Today's Lecture was a demonstration of process devices for:
- Flow Measurements
- Pressure Transducers
- Temperature Sensors
- Control Valves
Many of these devices are used in the Unit Operations Lab to measure and control the processes. Understanding the limitations and accuracy of these measurement devices is important in the design of a control application. The class notes give more detail on the control valves and selecting the correct characteristics for a particular service.
Discussion Questions
Test the lecture's ideas before or after class - commit to an answer first, then check it with a classmate or an AI tutor.
- A colleague sizes a control valve with a Cv three times the calculated requirement "for safety margin." Explain what an oversized valve does to the loop when it operates nearly closed, and why the margin hurts instead of helps.
- An equal-percentage valve is deliberately nonlinear, yet it is the common choice for many installed services. How can a nonlinear inherent characteristic produce a nearly linear installed characteristic?
- For a cooling-water valve on an exothermic reactor and a steam valve on a reboiler: choose fail-open or fail-closed for each, and state the safety consequence you are protecting against on loss of instrument air.
- Every sensor in the lecture has an accuracy specification. Why can the response time of a sensor matter more than its accuracy in a fast control loop?
App: Explore sizing and trim in the Valve Design app - compare linear and equal-percentage trim and watch the inherent characteristic morph into the installed characteristic as the valve's share of the system pressure drop changes.
