Fundamental function: In piping systems, are valves used to stop, start, throttle, or otherwise regulate the flow of fluids (liquids or gases) through a pipeline or piece of equipment?

Introduction / Context:
Valves are control elements that influence the behavior of process and building services systems. Recognizing their core purpose—stopping, starting, and regulating flow—is essential for reading piping and instrumentation diagrams (P&IDs), selecting components, and interpreting piping drawings. This question checks understanding at a foundational level applicable to many disciplines (mechanical, chemical, civil building services).

Given Data / Assumptions:

• “Fluid” includes liquids and gases.
• Pipelines may convey water, steam, air, oil, chemicals, or inert gases.
• Valves can be designed for on/off isolation or for modulation (control).

Concept / Approach:
Different valve designs serve distinct roles. Gate, ball, and plug valves often provide tight shutoff (isolation). Globe, butterfly, and control valves allow throttling for flow or pressure regulation. Check valves permit one-way flow to prevent backflow, and relief/safety valves protect against overpressure. Collectively, these functions satisfy the statement that valves stop or regulate flow in pipelines.

Step-by-Step Solution:

Verification / Alternative check:
Review manufacturer datasheets: flow coefficients (Cv), shutoff classes, and characteristic curves confirm each valve’s suitability for stopping or regulating flow under specified conditions.

Why Other Options Are Wrong:
“Incorrect” ignores the defining function. Limits to liquids, check valves only, or arbitrary pressure ceilings are unfounded; valves are designed across broad ranges of media and pressures.

Common Pitfalls:
Using isolation valves for throttling (e.g., gate/ball) where erosion or instability may occur; overlooking control rangeability; mis-sizing leading to poor authority in control loops.

Final Answer:
Correct