Which statement best compares pneumatic and electric actuators used with control valves?

• A. Pneumatic actuators use compressed air, are fast and simple but less precise
• B. Electric actuators use electrical power, offer higher precision, slower response, and flexible fail-safe options
• C. Pneumatic actuators are always slower and more accurate than electric
• D. Pneumatic actuators require more maintenance than electric and are less safe

Answer: (B)

The key idea is how the energy source and design of an actuator shape how a control valve moves, how precisely it can be positioned, and how safely it can fail over to a safe state. Pneumatic actuators, powered by compressed air, are fast and simple and can deliver strong motion, which makes them great for rapid open/close actions. But air is compressible and subject to leaks and supply variations, so controlling the exact position is harder and less repeatable than with electric actuation.

Electric actuators use motors and gears with feedback to position a valve very precisely. That higher positioning accuracy comes with a slower response because the motor and gearing take time to move to the commanded position, but the payoff is much finer control and the ability to hold a position reliably. They also offer flexible fail-safe options, such as brakes or locking mechanisms or spring-return configurations designed into the system, allowing safer or more reliable operation in power-off scenarios.

So, the statement that electric actuators run on electrical power, provide higher precision, have slower response, and offer versatile fail-safe options best reflects the typical trade-offs between the two technologies. The other descriptions oversimplify or misstate the performance and safety implications of pneumatic versus electric actuation.