Pressure Matching Control For One Closed Flat End Tubes

Meta: Pressure matching control for one closed flat end tubes, covering process port gauging, 1-1.2MPa high pressure, capillary cutting, bore selection and liquid supply throttling.

1. Core Industry Pain Points

One closed flat end tubes serve as refrigerant capillary throttling assemblies, and pressure matching failure is the most common hidden defect in compressor refrigeration systems. Many assembly teams randomly pick a capillary length and bore diameter without verifying actual system pressure. The result is overhigh or overlow high-pressure gauge reading at the process port. When pressure is too high, liquid supply is excessive, compressor overloads and the closed flat end tube expands; when pressure is too low, evaporator lacks refrigerant, sensor housing shows unstable temperature signal and cooling capacity drops obviously. A serious pain point is that technicians cut the capillary blindly or replace it with wrong bore size, breaking the flow balance. Because the closed end tube hides its lumen, internal blockage and uneven bore are hard to discover, causing delayed failure after the system runs for hundreds of hours.

2. Fundamental Working Principle

The pressure matching principle of one closed flat end tubes relies on the throttling characteristic of the capillary. Refrigerant passes through the capillary bore; flow volume is decided by bore diameter, length and inner roughness. Under a fixed compressor, the pressure difference between process port and capillary outlet reflects the throttling effect. Air is drawn in through the repair valve connected to the compressor process port and ejected from the open end of the capillary. When the low-pressure gauge at the process port equals atmospheric pressure, the high-pressure gauge connected between condenser outlet and filter should stay at 1–1.2MPa. This pressure window ensures proper superheat and liquid supply. If the high-pressure gauge is too high, cutting off a section of capillary shortens the flow path and reduces resistance. If it is too low, a longer or smaller-bore capillary increases resistance.

3. Equipment and Category Classification

Material options of one closed flat end tubes are mainly Stainless Steel 304 for ordinary air-conditioning and refrigeration sensors, and Stainless Steel 316 for corrosive and high-humidity scenes. Supporting equipment is divided into four modules. Measuring equipment includes low-pressure and high-pressure gauge sets, refrigerant manifold, repair valve and vacuum pump. Machining equipment covers cutting machine, grinding station, bending and swaging machine, plus cleaning station with nitrogen purge and acid-alkali tank. Tuning equipment includes spiral coiling fixture for adjusting flow resistance. Tube shapes are customized to round, oval, square and rectangular flat closed tubes according to 2D/3D drawing or sample. Surface treatment options include polishing, sandblasting, passivation and laser engraving. All products are certified under ISO9001:2015 and SGS.

4. Standard Operation Guide

Follow a strict pressure tuning workflow. First, connect the repair valve to the compressor process port, and connect high-pressure gauge between condenser outlet and filter. Second, evacuate the system and charge with refrigerant. Third, read the low-pressure gauge at process port; when it equals atmospheric pressure, check the high-pressure gauge reading. Fourth, judge according to window 1–1.2MPa. If high-pressure gauge is too high, cut a proper short section of capillary to lower flow resistance. If it is too low, replace with a longer capillary or a smaller-bore capillary. If the difference is small, coil the capillary into a spiral spring. The smaller the coil diameter and the more the turns, the higher the flow resistance and the high pressure. Fifth, after adjustment, complete cleaning and sealing of the closed flat end tube, then verify inner bore uniformity one by one for domestic raw material.

5. On-Site Practical Experience

From real compressor debugging, cutting capillary step by step is safer than one-time large cut, because flow resistance does not change linearly. Many operators cut too much and then waste time replacing the whole tube. The spiral coil method is underused: with only small deviation, coiling the capillary saves material and keeps the closed end tube intact. High-pressure gauge reading must be taken after the system stabilizes, not immediately after charging, otherwise reading is misleading. Capillary bore uniformity seriously affects tuning repeatability; uneven bore makes the same length behave differently. It is recommended to sort capillaries by measured bore grade before assembly.

6. Conclusion and Value

Pressure matching control turns one closed flat end tubes from a random throttling element into a predictable flow control device. Establishing the 1–1.2MPa high-pressure window as a unified tuning standard reduces on-site debugging time and compressor failure rate. Proper capillary cutting, bore selection and spiral coiling provide flexible adjustment paths, protecting the closed flat end tube and improving system reliability.

7. Industry Outlook and Suggestions

Future direction is auto pressure-balance tuning bench integrating gauges, data logging and closed-loop adjustment. Factories should standardize the pressure window and record tuning curves for traceability. Customers should specify bore tolerance and target pressure on drawings. For export refrigeration sensor projects, adopt SUS316 and provide batch SGS material report.