【Mechanical Equipment Technology Edition】Daily Question 201805021: Common Faults of Screw Refrigeration Compressors (5)
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This post was last edited by YORK Industrial Refrigeration on 2018-5-4 at 15:24. 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!) ) Those who comment on this post will receive 1-3 units of wealth as a reward; those who give complete answers will receive 10-15 units, with the reward valid for two days. ============================== Common faults of screw refrigeration compressors (5): During a business trip to Inner Mongolia, I noticed that the customers faced several common problems. I will focus on these issues here. The capacity display fluctuates sharply, jumping from 50 percent to 100 percent in an instant, with large and rapid fluctuations. What impact does this have on the refrigeration unit? How should such problems be solved? Answer: 1. Capacity mainly reflects the movement of the slide valve; it’s impossible for the slide valve’s movement to jump from 50 percent to 100 percent instantly! 2. The capacity display on the screen relies primarily on an energy sensor—the spool position sensor. 3. The slide valve displacement sensor is essentially a variable resistor; its damage causes fluctuations in the displayed values. 4. The capacity shown on the control center screen does not match the actual value – for example, if the actual level is 50%, it may be displayed as 100%, which prevents the unit from being loaded. The position of the slide valve can be estimated by considering the current value of the unit. 5. This phenomenon is similar to the old-fashioned radios used in childhood: when turning the volume knob, even a slight movement would result in very loud sound. The same is true here. ============================== High-quality promotions: Mechanical equipment——Videos on the repair and adjustment 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=
In my opinion, any compressor unit needs to operate within a stable range of parameters. In the case of screw compressors, large and rapid fluctuations can lead to increased energy consumption, as adjustments are required. Moreover, such fluctuations have negative effects on both the system and the compressor itself; for example, they can cause changes in the system’s load, which undermines system stability. For the compressor, these fluctuations can affect its internal components and increase the likelihood of failures. Improvements: It is necessary to strengthen inspections, check the cooling system and evaporation system for any issues, and adjust the stroke of the oil piston, among other things.
No standard answer has been found for this question; I have analyzed it based on my own understanding. I’m not sure if it reflects the actual situation, so please correct me if necessary: 1. The range of capacity changes is large and rapid. Capacity is defined from the perspective of the area served by the refrigeration unit; when capacity changes significantly and rapidly, the load on the refrigeration unit also changes accordingly. 2. When the unit load changes significantly and rapidly, the load control mechanism of the unit must operate frequently to make adjustments; over time, this increases component wear and the likelihood of failures. 3. When the load changes frequently, the various systems of the unit also change accordingly, which leads to frequent variations in the parameters of different components. This affects the stable operation of the unit, accelerates component damage, and shortens its lifespan. 4. The above changes will lead to increased energy consumption. Improvement methods: 1. The cause should be investigated from a cooling perspective, with efforts made to reduce capacity fluctuations. 2. Check the condition of the capacity detection and display components; any faults found should be resolved as soon as possible. 3. Check the operation of various systems in the unit and make targeted improvements. 4. If the load fluctuations cannot be improved, should the response speed of the automatic control system be slowed down slightly, in order to reduce the rate of system changes and thus lower the failure rate? I’m not sure if I’m right about one or two points; consider this just an attempt to stimulate further discussion.
The main reasons for large fluctuations in the slide valve are: 1. Issues with signal transmission; 2. Mechanical failures; 3. Large fluctuations in suction pressure. Such fluctuations can cause the chiller to cycle frequently between loading and unloading states, which puts stress on the machine’s components and may lead to damage. It is necessary to address each issue one by one before restarting the machine (I wrote this too vaguely……I still don’t seem to have understood the question fully)
If the thermal expansion valve is not compatible with the refrigeration system, it will cause the flow rate of refrigerant in the system to vary, which in turn results in fluctuations in the cooling capacity provided by the thermal expansion valve. When the cooling capacity is too low, it results in insufficient liquid supply to the evaporator, causing excessive superheat, which has an adverse effect on the performance of the unit’s system. When the cooling capacity is too high, oscillations occur, resulting in intermittent overfeeding of the evaporator. This leads to severe fluctuations in the suction pressure of the compressor, and liquid refrigerant may even enter the compressor, causing liquid slugging (wet stroke) phenomena.
The situation I have experienced, where unstable heat from heat sources led to frequent changes in the refrigerant load, easily triggered an interlock due to a high liquid level in the evaporator.
I still guessed the right direction, haha