3/4 HP Copper Capillary Tube Ø1.50 × Ø2.50 mm – Cap Tube, 15 kg and Multiples

Copper capillary tube is a fixed-bore copper tube with an inner diameter of Ø1.50 mm and an outer diameter of Ø2.50 mm. It acts as the expansion device in small and medium capacity refrigeration circuits: it throttles the high-pressure liquid refrigerant coming from the condenser down to evaporator pressure.

Capillary Tube: The Fixed-Bore Expansion Device of Small Refrigeration Circuits

Unlike a thermostatic expansion valve (TXV), it has no moving parts; the throttling effect is determined entirely by the tube's inner diameter and length. As a result, it does not fail, needs no adjustment and is very low in cost. On the other hand, its capacity is fixed — it cannot adjust itself when the load changes, so it is used in systems with a largely constant load.

This size is typically preferred for large display cabinets and refrigerated cabinets. When the compressor stops, the capillary tube allows the circuit pressures to equalize; it can therefore be used with RSIR-start (low starting torque) compressors.

Technical Specifications

• Inner Diameter: Ø1.50 mm | Outer Diameter: Ø2.50 mm | Wall Thickness: 0.500 mm
• Material: Electrolytic copper (Cu-DHP), refrigeration installation grade
• Applications: Refrigerators, freezers, display cabinets, bottle coolers, water dispensers and small commercial refrigeration circuits
• Compatibility: R134a, R600a, R290, R404A and other common refrigerants
• Sales Unit: 15 kg and multiples (coil) — the price is per kilogram
• Delivery Form: In coils (wound), clean and capped

• 🔧 Length calculation is critical: Even with the same inner diameter, a tube that is too short causes overfeeding (the evaporator floods, liquid reaches the compressor), and one that is too long causes underfeeding (capacity drops, excessive superheat). The length is determined by compressor capacity, refrigerant type and operating conditions.
• ✂️ Cutting method: Do not cut the capillary tube with a saw or side cutters — the burr narrows the bore and blocks the tube. Use a capillary tube cutter, or score and snap it; check the bore after cutting.
• 🧊 A filter drier is essential: A filter drier must always be fitted at the capillary tube inlet. The most common cause of failure is blockage by moisture and dirt; because the bore is very small, even the tiniest particle stops the flow.
• 🌡️ Heat exchange with the suction line: If part of the capillary tube is placed in contact with the suction line and soldered to it (heat exchanger effect), efficiency increases and liquid return to the compressor is reduced.
• Do not let filler metal run inside when brazing, and purge with nitrogen; oxide residue blocks the capillary tube.

What does the "3/4 HP" at the start mean?

In the trade, capillary tubes are referred to by the horsepower (HP) of the compressor they match. "3/4 HP capillary" means that this inner diameter is typically used in a circuit running with a 3/4 HP (three-quarter horsepower) compressor — it is not the power of the tube itself.

The logic is simple: as the compressor gets larger, the amount of refrigerant that must circulate in the circuit increases, so a capillary tube with a larger inner diameter is needed. Common equivalents:

• Ø0.80 mm → 1/6 HP  ·  Ø1.00 mm → 1/4 HP  ·  Ø1.20 mm → 1/3 HP  ·  Ø1.30 mm → 1/2 HP
• Ø1.50 mm → 3/4 HP  ·  Ø1.80 mm → 1 HP  ·  Ø2.00 mm → 1.5 HP

⚠️ This is a starting point, not a strict rule. The behavior of a capillary tube is determined by its length as much as by its inner diameter; in addition, the refrigerant type (R134a, R600a, R290…) and operating conditions (freezer / cooler) change the result. Even two systems of the same horsepower may require different lengths. For an exact selection, refer to the system manufacturer's table or a circuit calculation; if you are fitting an identical replacement for a removed tube, measure its length exactly as well.