What is the difference between direct-acting and reverse-acting control valves in BAS?

What is the difference between direct-acting and reverse-acting control valves in BAS?

• A. Direct-acting valves increase opening with increasing control signal.
• B. Direct-acting valves decrease opening with increasing control signal.
• C. They are the same.
• D. It refers to valve material.

Answer: (A)

In BAS control valves, action describes how the valve position responds to the control signal. A direct-acting valve is designed so that increasing the control signal makes the valve open more. In a typical 4-20 mA or similar loop, sending a higher signal ramps the actuator toward greater opening, increasing flow to reach the setpoint. A reverse-acting valve behaves in the opposite way: increasing the control signal causes the valve to close more or open less. This inverted response is used in certain control schemes or fail-safe configurations where a higher signal should reduce flow. So, the statement that direct-acting valves increase opening with increasing control signal correctly captures the defining behavior of direct-acting units.

In BAS control valves, action describes how the valve position responds to the control signal. A direct-acting valve is designed so that increasing the control signal makes the valve open more. In a typical 4-20 mA or similar loop, sending a higher signal ramps the actuator toward greater opening, increasing flow to reach the setpoint.

A reverse-acting valve behaves in the opposite way: increasing the control signal causes the valve to close more or open less. This inverted response is used in certain control schemes or fail-safe configurations where a higher signal should reduce flow.

So, the statement that direct-acting valves increase opening with increasing control signal correctly captures the defining behavior of direct-acting units.