The GATE Grind

GATE 2021 CH – Question 28

Instrumentation and Process Control · Controller modes, control valves and tuning · 1 mark · Multiple select

The inherent characteristics of three control valves P, Q and R are shown in the figure. The CORRECT option(s) is/are

percentage of maximum flow versus percentage of maximum lift. P rises steeply then flattens; Q is a straight diagonal; R rises slowly at first then steeply.
  1. P is a quick opening valve
  2. Q is a quick opening valve
  3. P is an equal percentage valve
  4. R is an equal percentage valve

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Show answer and explanation

Correct answer: (A) P is a quick opening valve; (D) R is an equal percentage valve

Explanation

A **quick-opening** valve provides a large fraction of its maximum flow at relatively small lift. Curve P has that shape, so A is true.

Q has flow proportional to lift and is a **linear** valve, so B is false. An **equal-percentage** valve has small flow increments at low lift and increasingly large increments at high lift: this is R, not P. Thus C is false and D true. **Answer: A and D.**