Which statement is not true about capillary tube metering devices?

Which statement is not true about capillary tube metering devices?

• A. They have no moving parts
• B. They are fixed restriction devices
• C. They meter flow based on differential pressure across the tube
• D. They can be adjusted with a variable valve

Answer: (D)

Capillary tubes meter refrigerant by creating a fixed pressure drop across a small-diameter, no-moving-parts tube. The flow that results is determined by the tube’s size and length and the differential pressure between the inlet and outlet, not by any adjustable mechanism. Because there is no adjustable valve or moving parts to regulate flow, you can’t tune a capillary tube in the field with a valve. If you need adjustable metering, a different device such as a thermostatic expansion valve would be used. The other statements are true: capillary tubes are fixed restriction devices, and the flow is governed by the differential pressure across the tube.

Capillary tubes meter refrigerant by creating a fixed pressure drop across a small-diameter, no-moving-parts tube. The flow that results is determined by the tube’s size and length and the differential pressure between the inlet and outlet, not by any adjustable mechanism. Because there is no adjustable valve or moving parts to regulate flow, you can’t tune a capillary tube in the field with a valve. If you need adjustable metering, a different device such as a thermostatic expansion valve would be used. The other statements are true: capillary tubes are fixed restriction devices, and the flow is governed by the differential pressure across the tube.