To understand why a shuttle valve is preferred over a two-way valve in systems with two independent control points for a single actuator, let's explore the working principles of these valves and their applications:

Understanding Shuttle Valve

A shuttle valve is a type of valve that allows fluid flow from one of two sources to actuate a common output. It has three ports: two inputs and one output. The valve functions by automatically selecting the input with the higher pressure to pass through to the output while blocking the other input. This unique function makes shuttle valves ideal in scenarios where control of an actuator from two distinct points is desired without interference.

Purpose of Using Shuttle Valve

• Selective Control: The shuttle valve allows the operation of an actuator from either of the two control points without signal interference or loss. This means that whichever control point provides a signal, the shuttle valve will direct that signal to the actuator.
• Independent Control Points: Both control points can be connected to the shuttle valve, and the system ensures that the actuator receives commands from only one active point at any time, thus preventing conflicting signals.

Why Other Options are Incorrect

• Option A: A shuttle valve does allow only one control point to function at a time, but it doesn't necessarily block the other; it merely takes the higher pressure signal.
• Option B: Shuttle valves do not discharge air from both control points; they select one signal based on pressure dominance.
• Option C: While shuttle valves prevent simultaneous operation, they do not "interlock" signals but select based on the higher pressure signal from the inputs.

Therefore, the correct answer is that A shuttle valve enables actuator operation from either control point without signal interference or loss.