Which statement correctly characterizes a key difference between discrete control valves and proportional control valves?

• A. Discrete control valves require analog input to modulate flow.
• B. Proportional control valves adjust flow continuously in response to analog signals.
• C. Both of the above statements are correct.
• D. Neither of the above statements is correct.

Answer: (B)

The key distinction is how the valve responds to input signals: discrete valves operate in an on/off fashion, while proportional valves change flow continuously in proportion to the analog input. Discrete valves typically receive a digital or binary signal that fully opens or fully closes the valve (or moves through a limited number of fixed positions), so the flow is not smoothly scaled. Proportional control valves, however, interpret an analog signal (such as a voltage or current) and adjust the valve opening gradually, giving a continuous range of flow—from very small to very large. That continuous modulation is what makes these valves capable of fine-tuned control. Therefore, the statement that proportional control valves adjust flow continuously in response to analog signals is the correct distinction.