Vacuum Extraction Standards and Moisture Control of Cold Storage Systems | Vacuum Extraction Standards after New Machine Installation and Major Maintenance
Residual moisture in the refrigeration system is the source of chronic damage to the compressor. Moisture and POE refrigerant oil hydrolyze, generating organic acids that continuously corrode valve plates, motor insulation, and bearings.
The standard evacuation of cold storage is divided into two levels. The first level is roughly evacuated to 500Pa and left to stand and maintain pressure for 30 minutes; The second level precision vacuum is maintained at a maximum vacuum of 100Pa or below, and the vacuum is continuously evacuated for no less than 4 hours.
The Xitelidou compressor condensing unit is sealed with positive pressure nitrogen inside the factory. After unpacking, it should be welded as soon as possible to avoid prolonged opening and the entry of water vapor from the air into the pipeline.
The entire welding pipeline is protected by nitrogen gas to reduce the oxide scale on the inner wall of the pipeline. Impurities from the oxide scale entering the compressor will accelerate the wear of the cylinder body and valve plate, and shorten the service life of the equipment.
Many engineering companies only take half an hour to add refrigerant, and the water in the system cannot be completely extracted. In the short term, normal operation may occur, and after 3-6 months, ice blockage and oleic acid failure may occur one after another.
After the negative pressure evacuation is completed, the vacuum pump cannot be immediately shut down. The system side valve must be closed first, and then the vacuum pump must be stopped to prevent the vacuum pump oil from flowing back into the refrigeration pipeline and contaminating the system.
The cryogenic R23 unit has extremely low tolerance for moisture, with an extended evacuation time of 8 hours and a vacuum level maintained within 50Pa. After evacuation, nitrogen pressure is maintained for 24 hours for leak detection.
The vacuum pump equipment on overseas construction sites varies greatly, and the technical documents of foreign trade projects will specify the accuracy requirements of the vacuum gauge. It is recommended to use a digital vacuum gauge instead of relying on a simple pressure gauge for rough judgment.
The cost of handling water ingress accidents in the system is very high, requiring the complete emptying of the refrigerant, replacement of the refrigeration oil, and continuous replacement of the drying filter twice, repeatedly emptying, which takes much more time than the standard emptying.
In addition to the vacuum degree, the determination of qualified evacuation also depends on the holding pressure. Close the vacuum pump valve and let it stand for 2 hours. Only when the pressure rises no more than 150Pa can it be considered qualified evacuation.
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FAQ
What are the requirements for the second level precision vacuum degree of conventional cold storage? Precision pumping target vacuum degree below 100Pa.
2. What is the minimum duration of regular precision aspiration? Fine vacuum extraction for no less than 4 hours.
3. After evacuating, should we turn off the pump or the valve first? Close the system valve first, and then shut down the vacuum pump.
4. How much is considered qualified when the pressure rises during the holding and static period? Let it stand for 2 hours and the rebound should not exceed 150Pa.
What are the requirements for the evacuation time of R23 cryogenic units? It is recommended to evacuate for no less than 8 hours and maintain a vacuum of no more than 50Pa.
Why is nitrogen gas introduced during welding? Prevent the formation of oxide scale impurities on the inner wall of the pipeline.
What faults may occur in the later stage if the idle time is too short? Ice blockage, frozen oil acidification, and component corrosion.
