Which statement about capillary tubes is true?

Which statement about capillary tubes is true?

• A. They have moving parts
• B. They are fixed restriction devices
• C. They actively regulate flow with a control valve
• D. They require a separate electrical power source

Answer: (B)

Capillary tubes act as a fixed restriction device: they have no moving parts and don’t require any electrical power to operate. The metering happens simply because the tube’s small, fixed diameter and length create a constant pressure drop as refrigerant flows from the high-pressure liquid side into the evaporator. Since there’s no valve or actuator to adjust flow, the amount metered into the evaporator depends on the pressure conditions and the refrigerant properties at that moment. This makes their performance straightforward but less flexible than devices with active regulation, such as thermostatic or electronic expansion valves.

Capillary tubes act as a fixed restriction device: they have no moving parts and don’t require any electrical power to operate. The metering happens simply because the tube’s small, fixed diameter and length create a constant pressure drop as refrigerant flows from the high-pressure liquid side into the evaporator. Since there’s no valve or actuator to adjust flow, the amount metered into the evaporator depends on the pressure conditions and the refrigerant properties at that moment. This makes their performance straightforward but less flexible than devices with active regulation, such as thermostatic or electronic expansion valves.