Capillary tube metering devices are best described as

• A. Fixed restriction devices
• B. Variable restriction devices
• C. Electrically controlled valve devices
• D. Pressure-regulating valves

Answer: (A)

Capillary tube metering devices are fixed restriction devices. They have a very small, fixed bore and no moving parts, so they don’t actively regulate flow. The refrigerant's passage through the tube is determined by the pressure difference between the condenser (high side) and the evaporator (low side) and the refrigerant’s properties. Because the restriction cannot adjust, the amount of refrigerant that flows changes with operating conditions, making the system simple and inexpensive but less able to compensate for varying loads. This contrasts with variable restriction devices, such as thermostatic expansion valves, which actively adjust the flow to maintain desired evaporator conditions.