[Mechanical Equipment Technology Edition] Daily Question 20180201: Common Faults in Refrigeration Systems (8.8)
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This post was last edited by YORK Industrial Refrigeration on 2018-2-5 at 11:49. Starting from now, in order to enhance communication among members, a \"Question of the Day\" campaign has been launched on the Mechanical Equipment Technology forum. We hope everyone will participate actively to progress and improve together! ! ! Rewards: 3 wealth points for active participation, 10-15 wealth points for correct answers. This question is valid for two days; no score will be given after that period. I’m sure everyone has experienced the maintenance of refrigeration units. The most basic components that require maintenance include the oil filter, dryer element, refrigerant, and oil separator. Why is it necessary to replace these parts? How do you understand it? 1. Screw compressors are mechanical devices, and as such they experience wear and tear. Therefore, oil is used to create an oil film between their contacting surfaces. However, over time the oil undergoes chemical changes, leading to changes in its properties that accelerate the wear of the compressor. Hence, it is essential to maintain the quality of the oil, which is why it needs to be replaced. 2. As the compressor operates for an extended period of time, its components age. The bearings serve to support the screw; if they deform, it can cause the screw to move axially and radially, leading to wear on the compressor. Impurities can enter the oil filter, blocking it and affecting the oil supply pressure. This is why the oil filter needs to be replaced. 3. The oil filter primarily serves to separate oil from gas; otherwise, it will affect the return of oil, so it needs to be replaced or cleaned. 4. The dryer filter is used mainly to remove water – water entering the system can contaminate the refrigerant and oil as well as cause corrosion. ============================== Premium promotions: Mechanical equipment – Maintenance procedures for York screw compressors https://bbs.hcbbs.com/thread-1806833-1-1.html Mechanical equipment – Upgrading York Quinton control centers https://bbs.hcbbs.com/thread-1804837-1-1.html Mechanical equipment – Major repairs for GEA Grasso 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 MYCOM screw compressors https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=
Due to mechanical wear, powder-like mechanical impurities clog the filter screen, reducing the filtering efficiency
When the compressor is in operation, iron shavings are generated inside the pipes and within the components, resulting in some wear. Lubricating oils and refrigeration oils can become emulsified or deteriorate over time, so they need to be replaced regularly or as needed.
Prolonged use of the filter element leads to clogging, which affects the filtering efficiency； Freezing oil and refrigerants also need to be replaced regularly to ensure optimal cooling performance.
The main aspects of refrigeration unit maintenance include routine care and periodic inspections. Regular maintenance ensures the long-term proper operation of the unit, extends its service life, and also helps to save energy consumption for cooling. For chillers, there should be operation records that document the performance of the units, and maintenance technical files must also be established. Complete technical documentation helps identify potential faults, allowing timely action to be taken to prevent their occurrence. The compressor of a refrigeration unit is a very critical component; the quality of the compressor directly affects the stability of the unit. If the compressor fails, due to the high precision requirements for its installation, it is usually necessary to have the manufacturer carry out the repairs. 1. Replace the lubricating oil: After long-term use, the quality of the lubricating oil in a refrigeration unit deteriorates, with an increase in impurities and moisture within it; therefore, it is necessary to regularly monitor and check the quality of the oil. Once a problem is detected, it should be replaced promptly, and the grade of the lubricating oil used for replacement must comply with the technical specifications. 2. Replace the dry filter. The dry filter is an important component that ensures proper circulation of the refrigerant. Since water and refrigerant are immiscible, the presence of water in the system will **affect the operational efficiency of the unit; therefore, it is very important to keep the system dry. The filter elements inside the dryer-filter must be replaced regularly. 3. Calibration of safety valves The condenser and evaporator in a chiller unit are both considered pressure vessels. According to regulations, a safety valve must be installed at the high-pressure end of the unit, that is, on the condenser itself. In case the unit operates under abnormal conditions, the safety valve can automatically release pressure, thereby preventing potential harm to people caused by high pressures. Therefore, the regular calibration of the safety valve is extremely important for the safety of the entire unit. 4. Cleaning of the condenser and evaporator In water-cooled condensers, the cooling water uses an open-loop circulation system; generally, tap water is recycled through a cooling tower. When the levels of calcium and magnesium salts in water are high, they tend to decompose and deposit on the cooling water pipes, forming scale that affects heat transfer. Excessive scaling also reduces the flow cross-section of the cooling water, decreases the water volume, and raises the condensation pressure. Therefore, when the quality of the cooling water used is poor, the cooling water pipes should be cleaned at least once a year to remove scale and other contaminants from within them. There are generally two methods for cleaning the water pipes in a condenser: (1) Using a specialized pipe-cleaning gun to clean the pipes. (2) Use a specialized cleaning agent for cyclic flushing, or add it to the cooling water; wait for 24 hours before changing the solution until it is thoroughly cleaned. 5. Refrigerant charging Unless there are other special reasons, normal units do not experience significant leaks. If a certain amount of refrigerant leaks due to improper use or after maintenance, it is necessary to add more refrigerant. When charging the refrigerant, attention must be paid to the grade of refrigerant specified for the unit.
The most basic maintenance components – the dry filter element, refrigeration oil, refrigerant, and oil filter element – why do we need to replace these parts? How do you understand it? Answer: 1. Replacing the oil filter and oil element is necessary to ensure the oil pressure difference ； 2. Replace the desiccant: To ensure the system’s dew point ； 3. Replace the refrigeration oil and refrigerant: This is necessary to ensure that the system can meet the production requirements ；
Due to mechanical wear, powder-like mechanical impurities clog the filter screen, reducing the filtering efficiency
The replacement of various filter elements is mainly due to blockages or loss of effectiveness that occur after the unit has been in operation for a long time. For example, oil filters are affected because the refrigerant inside the unit passes through these filters every time it operates; over time, various impurities such as welding slag and copper shavings accumulate within the filter elements. Frozen oil and refrigerant are akin to the lubricating oil in a car or the refrigerant in a car’s air conditioning system; efficiency losses or leaks occur as a result of long-term operation. Of course, this is an essential part for the unit to maintain long-term stable operation.
Because these are vulnerable components or liquids that can deteriorate, it is very difficult to clean them thoroughly by hand.
This post was last edited by “Hasty Passerby” on February 2, 2018, at 08:19. Why is it necessary to replace spare parts such as oil filters, dryer elements, refrigeration oil, refrigerants, and oil separator elements? 1. Functions of the three types of filters and reasons for replacement: The oil filter is used to further remove metal particles resulting from the wear of various components in the oil, as well as gel-like particles formed due to chemical reactions in the system fluid, thereby extending the service life of the compressor; hence it needs to be replaced regularly. The dry filter is an important component that ensures the proper circulation of the refrigerant. Since water and refrigerant are immiscible, the presence of water in the system will **affect the operational efficiency of the unit; therefore, it is very important to keep the system dry. The filter elements inside the dryer-filter must be replaced regularly. The oil-gas separation filter element is installed in the compressor’s oil-gas separator to remove oil mist and solid particles from the compressed air, thereby providing a clean air supply for the systems downstream of the compressor; hence, it needs to be replaced regularly. 2. Reasons for replacing refrigeration oil: 1) Refrigeration oil ages over time, and even when the compressor is not in use, its various performance parameters gradually decline. 2) When the compressor is operating, the high pressure and high temperature cause the lubricating oil to degrade, gradually losing its lubricating function. 3) System moisture causes contamination, acidification, and erosion of the motor. 4) Foreign objects or metal shavings get mixed in, contaminating the lubricant and clogging the oil filter. Monitoring parameters for refrigeration oil and recommendations for replacement: 1) pH value: The acidification of lubricating oil can corrode the surfaces of the compressor screws, bearings, as well as the insulation coating on the motor, directly affecting the lifespan of the compressor motor. This leads to increased operating noise, a decrease in compression ratio, and necessitates premature major repairs of the compressor. Therefore, the acidity of the lubricating oil should be checked regularly to ensure it is within acceptable limits. Generally, lubricating oil should be replaced when its acidity is below pH 6. If it is not possible to check the acidity, the system’s dry filter should be replaced regularly to maintain the system’s dryness at normal levels. 2) Pollution index: Excessive contaminants in the refrigeration oil can cause premature wear of the bearings, an increase in clearance, and higher noise levels; it is therefore necessary to replace the bearing sets in advance. If the contamination level in 100 ml of refrigerant oil exceeds 5 mg, it is recommended to replace the refrigerant oil. 3) Moisture content: When the moisture content is too high, it goes without saying that the lubrication properties deteriorate, as does the insulation performance; this makes it very easy for the motor to be damaged or burned out. Above 100 ppm, the refrigeration oil needs to be replaced. 4) Color of the refrigeration oil: The majority of refrigeration oils are colorless, transparent, and clear. If their color darkens, this can be observed visually through the sight glass of the compressor, and this can also serve as a simple criterion for determining when it is time to replace the refrigeration oil. 3. Reasons for replacing the refrigerant: The refrigerant gradually decreases over time due to factors such as leaks, so it needs to be replenished periodically or as needed. Additionally, it has a limited service life; once it reaches that limit or becomes contaminated (it’s not certain whether contamination is possible), it must be replaced.
Answer: After operating for a long time, refrigeration units experience mechanical wear, which causes powder-like mechanical impurities to clog the filters, thereby reducing their filtering efficiency. When used for a long time, refrigeration oil can develop carbon deposition and emulsification, resulting in a reduced lubricating and cooling effect. 1. Replacing the oil filter and oil element is essential to maintain the oil pressure difference ； 2. Replace the desiccant: To ensure the system’s dew point ； 3. Replace the refrigeration oil and refrigerant: This is necessary to ensure that the system can meet the production requirements ；