Final answer:
The statement is true; pressure-actuated compressor control is generally not viable for systems with automatic expansion valves or capillary tubes because these components do not maintain the constant pressure necessary for such controls to function effectively.
Step-by-step explanation:
The statement that pressure-actuated compressor control cannot be used in systems using automatic expansion valves or capillary tubes is generally true. The reason for this is that pressure-actuated controls are designed to modulate the compressor's operation based on the suction or discharge pressure of the system. Automatic expansion valves and capillary tubes, however, regulate the refrigerant flow based on cooling load and are not designed to provide the constant suction pressure needed for pressure-actuated compressor control to work effectively. In such systems, using pressure-actuated controls would not allow for proper regulation of the compressor, potentially leading to system inefficiency or failure.
Gases, such as those used in pneumatic systems, are compressible and therefore behave differently under pressure compared to liquids, which are essentially incompressible. This is highlighted by Boyle's law, which states that the pressure of a gas is inversely proportional to its volume. Hydraulic systems leverage this property of liquids for consistent force transmission throughout the system.
Making further connections, the principle of conservation of energy implies that a hydraulic system cannot do more work than the energy input to it. This concept underlines the importance of using the appropriate medium—typically a liquid—in hydraulic systems for optimal functionality, something that's not as efficient when gases with different compressibility are used.