Copper capillary tubes possess excellent pressure resistance, classifying them as high-pressure tubing. Despite their small diameter and thin walls, thanks to the high strength and good toughness of copper (such as TP2), they can withstand pressures far exceeding those required by typical household refrigeration systems.
The following is a detailed analysis of the pressure resistance performance of copper capillary tubes:
1. Specific Pressure Resistance Range
The pressure resistance of copper capillary tubes is directly related to their outer diameter, wall thickness, and material state (hard or soft). According to relevant industrial standards (such as GB/T 1531) and material characteristics:
* Airtightness Test Pressure: For high-precision copper capillary tubes, the airtightness test pressure is typically required to be between 2.0 MPa and 7.8 MPa (approximately 20 to 78 kgf/cm²), and must remain leak-free for 30-60 seconds.
* Tubing with a wall thickness difference of 0.2~0.5 mm typically has lower pressure resistance (approximately 2.0 MPa). * Pipes with a wall thickness difference of 0.7~1.8mm can withstand pressures of 6.9~7.8 MPa.
* Burst Pressure: The burst pressure of copper pipes is much higher than the working pressure. Generally speaking, the pressure resistance of copper pipes is several times or even tens of times that of plastic pipes (such as PPR and PVC). At room temperature, qualified copper capillary tubes for refrigeration can typically withstand pressures of over 10 MPa (100 kg) without rupturing.
2. Key Factors Affecting Pressure Resistance
* Wall Thickness (Critical): This is the most crucial parameter determining pressure resistance.
* For example, a capillary tube with an outer diameter of 2mm and a wall thickness of 0.5mm has a much higher pressure resistance than a similarly sized tube with a wall thickness of 0.3mm.
* Industrially, pressure resistance stability is typically ensured by controlling wall thickness unevenness (not exceeding 10% of the nominal wall thickness), preventing bursts at weak points caused by eccentricity.
* Material State (Hard vs. Soft):
* Hard State (Y-state): Tensile strength ≥ 345 MPa, stronger pressure resistance, but more difficult to bend.
* Soft State (M-state): Annealed, elongation ≥ 40%, slightly lower strength than the hard state, but better toughness, stronger resistance to impact and vibration fatigue, suitable for complex installation environments.
* Temperature Effect:
* Low Temperature: Copper pipes have the characteristic of "high strength at low temperatures." Unlike ordinary plastic pipes that become brittle at low temperatures, copper pipes can maintain their shape and strength even at extremely low temperatures of -183℃ without cracking.
* High Temperature: Copper has a melting point as high as 1083℃. Although the metal strength decreases slightly with increasing temperature, its pressure resistance is very stable within the operating temperature range of refrigeration and general industrial pipelines (-50℃ to 200℃), and it will not exhibit aging or rapid pressure drop like plastic pipes.
3. Pressure Resistance Performance in Real-World Applications
* Refrigeration Systems: The operating pressure of refrigerants (such as R410A and R32) in household air conditioners and refrigerators is typically around 2.0–4.5 MPa. Copper capillary tubes, as throttling elements, are designed with a large pressure tolerance margin, fully capable of safely handling these pressures and pressure fluctuations.
* High-Pressure Instruments: In precision instruments, copper capillary tubes are often used as pressure measuring tubes, directly connected to high-pressure sources, directly demonstrating their ability to withstand high-pressure pulses.
Summary
Copper capillary tubes are high-strength, pressure-resistant tubing.
* General Safe Operating Pressure: Typically, pressures below 6 MPa (60 kg) are very safe.
* Ultimate Pressure Resistance: Depending on wall thickness, it can reach over 10 MPa.
* Advantages: Compared to plastic tubing, it maintains stable pressure resistance in extremely low (non-brittle) and high (non-softening) environments, and has good fatigue resistance, making it suitable for long-term pressure fluctuation conditions.
