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How to check the air tightness of the refrigeration system

How to check the air tightness of the refrigeration system

  • 2020-11-12

The refrigerants currently used (especially Freon-type refrigerants) have a strong permeability, and therefore, the refrigeration system is required to have good air-tightness. After the completion of the blowdown work, the refrigeration system must be carefully and meticulously tested for air tightness.


The air tightness test is generally divided into three methods: pressure test, vacuum test and working test:


1 Stress test

The magnitude of the test pressure is usually determined by the difference in the type of refrigerant used in the refrigeration system and the test site.

(1) The nitrogen bottle is connected to the exhaust multi-channel of the refrigeration compressor through a pressure reducing valve.

(2) Close all valves of the refrigeration system to the atmosphere except the exhaust bypass, and open all the valves in the system.

(3) Open the nitrogen bottle valve, let the system first increase the nitrogen pressure to 0.3 ~ 0.5MP, do the initial test leak, and consider that after the basic no leakage, the specific pressure test is carried out on the high pressure part and the low pressure part respectively.

(4) Pressurize the test pressure value to the low pressure system. After the pressure is balanced, record the specific reading of the pressure gauge and the ambient temperature. Keep 6L, allow the pressure drop to be below 0.02MP, and continue to maintain 18~24L. If the ambient temperature does not change much, if the gauge pressure does not change, it is considered that the low pressure pressure test leak is qualified.

(5) Close the shut-off valve or manual bypass valve before the thermal expansion valve, and only pressurize the high pressure part of the system to the test pressure value of the high pressure system. After the pressure is balanced, record the specific reading of the pressure gauge and the ambient temperature. Maintain 6L, allow pressure drop in 4 small refrigeration systems. Pressure tests must be performed with dry nitrogen.


2 Vacuum test

Vacuum leak test is to let the refrigeration system under a proper vacuum for a certain period of time, whether the reading of the vacuum gauge changes to reflect whether the air penetrates into the system to verify the sealing performance of the system. This test must be performed for refrigeration systems where the evaporation pressure is near or below atmospheric pressure.


3 Working fluid test

Due to the high permeability of refrigerants such as Freon, when there are only small leaks in the system, it is often difficult to determine whether the system has a leak hazard by using only the above two methods. Therefore, such a system also requires a test leak. The basic method of working fluid leakage test is that the system is filled with vacuum and charged with the same refrigerant as the refrigerant used in the system. The charge is equal to about 0.1 MP lower than the ambient pressure at ambient temperature.

If the system can maintain 16 to 24L without pressure drop, it is considered that the working fluid test is qualified. The test fluid leakage can also be carried out by the following method: first, the working medium is filled with a working pressure of 0.1 to 0.2 MP, and then filled with dry nitrogen to make the total atmospheric pressure reach 0.8 to 1 MP. If the system can maintain 16 to 24L without pressure drop, it is considered that the working fluid test is qualified. This method has a higher test success rate.

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