[Mechanical Equipment Technology Edition] Daily Question 201805003: Common Faults of Screw Refrigeration Compressors (6)
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This post was last edited by YORK Industrial Refrigeration on 2018-5-5 at 08:19. This year’s 【Daily Question】is divided into three categories: screw refrigeration compressors, refrigeration systems, and oil circuits, aiming to provide a comprehensive understanding of refrigeration technology. (If you encounter something you don’t know or can’t answer, please actively look up information; as you do so, your skills will improve!) ) All participants in the comments on this post will receive 1-3 wealth points; those who give complete answers will get 10-15 points, with the rewards valid for two days. ============================== Common faults of screw refrigeration compressors (5): I visited this customer’s facility, and due to low load, the equipment operated at a low capacity for extended periods. The temperature of the cooling water was high, resulting in poor condensation, and the equipment generated a lot of noise. By applying manual loading, the noise level of the equipment decreased gradually. Question: Why does the refrigeration compressor vibrate more when the load is low, and vibrate less when the load is high? Answer: It involves a issue of the ratio between internal pressure and external pressure. When the internal pressure ratio is greater than the external pressure ratio, it is called overcompression; when the external pressure ratio is greater than the internal pressure ratio, it is called undercompression. The latter condition leads to high-pressure gas from the exhaust side flowing back toward the intake side, causing severe vibrations in the compressor, similar to the surge phenomenon in centrifuges. ============================== High-quality promotions: Mechanical equipment——Videos on the repair and calibration of York compressors https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=1806833 Mechanical equipment——Maintenance procedures for York screw compressors https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=1806833 Mechanical equipment——Upgrading of York Quinton control centers https://bbs.hcbbs.com/thread-1804837-1-1.html Mechanical equipment——Major repairs of GEA Grasox screw compressors https://bbs.hcbbs.com/thread-1800467-1-1.html Mechanical equipment——Disassembly and maintenance of British HOWDEN screw compressors https://bbs.hcbbs.com/thread-1832529-1-1.html Mechanical equipment——Disassembly and maintenance of Japanese Maekawa MYCOM screw compressors https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=
At low loads, the flow rate of the refrigerant is low, making surge easily occur; this phenomenon does not happen at high loads.
At low loads, the flow rate of the refrigerant is low, making surge easily occur; this phenomenon does not happen at high loads.
At low load levels, gas flows back more extensively inside the compressor, resulting in greater vibration. As the load increases, the amount of backflow decreases, the unit becomes more stable, and the vibration also reduces (I’m not sure if this is correct)
At low loads, the flow rate of the refrigerant is low, making surge easily occur; this phenomenon does not happen at high loads.
At low loads, the flow rate of the refrigerant is low, making surge easily occur; this phenomenon does not happen at high loads
At low loads, the flow rate of the refrigerant is low, making surge easily occur; this phenomenon does not happen at high loads.
The screw compressor is not surging. Increase the speed to avoid the resonance point
When the load on the refrigeration compressor is low (in automatic load adjustment mode): 1. After adjustment by the automatic load control system, the amount of reflux increases significantly, and this large volume of reflux can cause a certain level of vibration. 2. As stated in the problem: high cooling water temperature leads to poor condensation, increased condensation pressure, elevated exhaust pressure, and a greater pressure difference between the exhaust and intake pressures; this further increases the pressure difference during backflow, thereby affecting vibrations. 3. A poor condensation effect can result in refrigerant being carried in the return oil (which is equivalent to an excessive amount of oil); more liquid present during reflux can lead to increased vibration. At high load: the backflow decreases, most of the refrigerant enters the circulation system, the condensation effect improves, and the vibrations caused by backflow are naturally reduced.
I’ve learned something new again; daily questions are really great
It involves a issue of the internal pressure ratio compared to the external pressure ratio; when the internal pressure ratio is greater than the external pressure ratio, it is called overcompression, while when the external pressure ratio is greater than the internal pressure ratio, it is called undercompression. The latter condition leads to high-pressure gas from the exhaust side flowing back toward the intake side, causing severe vibrations in the compressor, similar to the surge phenomenon in centrifuges.