Common oil deficiency faults in vortex refrigeration compressors

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　　Prolonged lack of oil in the compressor – overheating of the mechanical components and various friction pairs, resulting in bearing sintering and shaft seizure. 　　Short-term oil shortage in the compressor – abnormal wear of the mechanical components and various friction pairs, resulting in excessive vibration and noise. I. How to ensure an appropriate amount of oil 　　When the compressor discharges refrigerant, it also releases a small amount of refrigeration oil. Even with a lubrication rate of only 0.5%, if the oil cannot circulate back to the compressor through the system. Taking 5HP as an example, if the flow rate is around 330 kg/h under ARI conditions, all the oil in the compressor can be removed within 50 minutes; the compressor will then be damaged within approximately 2 to 5 hours. Therefore, to ensure that the compressor operates without a lack of oil, action should be taken in the following two areas: 1. Ensure that the refrigeration oil discharged from the compressor returns to it. 　　2. Reduce the oil supply rate to the compressor. (Frequent startup of the compressor is not conducive to oil return.) ) II. How to ensure that the discharged refrigerant oil returns to the compressor 　　1. The flow rate of the refrigerant in the suction pipe should be around 6 m/s in order for the oil to return to the compressor; however, the maximum flow rate should be less than 15 m/s to reduce pressure drops and flow noise. For horizontal pipes, there should also be a downward slope in the direction of refrigerant flow, of about 0.8 cm/m. 　　2. Prevent refrigeration oil from remaining in the evaporator. 　　3. Ensure that the oil return hole of the gas-liquid separator is of appropriate size; if it is too large, wet compression will occur, while if it is too small, insufficient oil will return, causing oil to remain stagnant in the gas-liquid separator. 　　4. There should be no areas in the system where oil can accumulate. 　　5. Ensure that there is sufficient refrigerant oil in the compressor even when dealing with long pipes and large height differences; this is usually checked using a compressor equipped with an oil level gauge. III. How to reduce the oil feeding rate of the compressor 1. When shutting down the machine, it is necessary to ensure that the refrigerant does not dissolve into the compressor oil (use a crankshaft heater). 　　2. Avoid operating in overly humid conditions, as this can lead to excessive oiling due to bubbling. 　　3. Install an internal oil separator device. 　　4. Bubbling of the oil inside the compressor makes it easy for the oil to be carried out of the compressor. IV. Long piping and large pressure drops When the length of the piping exceeds the allowable value, the pressure loss within the piping increases, which reduces the amount of refrigerant in the evaporator and leads to a decrease in performance. At the same time, when oil remains inside the piping, it causes a lack of oil in the compressor, leading to compressor failures. When there is insufficient refrigerant oil in the compressor, refrigerant oil of the same grade as that used at the time of the compressor’s manufacture should be added from the high-pressure side. V. Necessity of installing an oil return elbow When the height difference exceeds 10m to 15m, an oil return elbow should be installed on the side of the air pipe. 　　Necessity: During shutdown, prevent the refrigeration oil attached to the piping from returning to the compressor, which could cause liquid compression. On the other hand, this is to prevent a lack of oil in the compressor due to poor return of oil to the air duct. 　　Interval for oil return bends: An oil return bend is installed every 10 meters of drop. VI. How to Ensure the Appropriate Viscosity of Refrigeration Oil 　　1. Refrigeration oil and refrigerant are mutually soluble; when the machine is shut down, almost all of the refrigerant dissolves in the refrigeration oil. Therefore, a crankshaft heater must be installed to prevent this dissolution. 　　2. During operation, the refrigerant containing liquid should not return to the compressor, thereby ensuring a superheat in the compressor’s suction air. 　　3. No backflow of liquid should occur during startup and defrosting. 　　4. Avoid operating under conditions of excessive overheating to prevent oil degradation. 　　5. The size of the oil return hole in the gas-liquid separator should be appropriate: ① If the hole diameter is too large, liquid refrigerant will be drawn in, resulting in over-wet operation; ② If the hole diameter is too small, oil return will be hindered, causing oil to remain in the gas-liquid separator. VII. Main reasons for damage to the compressor motor 1. Abnormal loads and stall. 　　2. Winding short circuit caused by metal shavings. 　　3. Contactor issues. 　　4. Power supply phase loss and voltage abnormalities. 　　5. Insufficient cooling. 　　6. Use a compressor to create a vacuum. VIII. Main reasons for abnormal load or stall An excessive pressure ratio, or a large pressure difference, can make the compression process more difficult ； The increased frictional resistance caused by lubrication failure, as well as motor stall under extreme conditions, will **increase the motor load**. If the load increases to the point that thermal protection is activated and the protection mechanism resets automatically, a vicious cycle of \"stall – thermal protection – stall\" will occur. Frequent startups and abnormal loads subject the windings to high temperatures, which reduces the insulation properties of the enameled wire. Once the insulation performance of the windings deteriorates, other factors (such as metal shavings forming a conductive path, acidic lubricants, etc.) can easily lead to short circuits and damage. 　　1. Winding short circuits caused by metal shavings Sources of metal shavings include copper tube shavings left over from construction, welding slag, as well as metal shavings that result from wear and damage to components inside the compressor. During operation, driven by the airflow, these metal shavings or fragments fall onto the windings. The normal vibration of the compressor during operation, as well as the twisting of the windings due to electromagnetic forces each time it starts up, cause relative movement and friction between the metal shavings trapped among the windings and the enameled wires of those windings. Sharp metal shavings can scratch the insulation layer of the enameled wire, causing a short circuit that leads to the motor burning out. 　　2. Contactor issues 　　For safety and reliability, the compressor contactor must disconnect all three phases of the circuit at the same time. Contactors must be able to meet harsh conditions such as rapid cycling, continuous overload, and low voltage. They must have a large enough area to dissipate the heat generated by the load current, and the contact material chosen must prevent welding under conditions of high current such as startup or stall. Otherwise, once the contacts of the contactor weld together, all controls that rely on the contactor to disconnect the power supply to the compressor (such as high/low pressure control, temperature control, defrost control, etc.) will cease to function, leaving the compressor without any protection. Therefore, checking the contactor is an essential step after the motor burns out. 　　3. Power supply phase loss and voltage abnormalities The voltage range of the power supply must not exceed ±10% of the rated voltage. The voltage imbalance between the three phases must not exceed 3%. If a phase loss occurs while the compressor is running, it will continue to operate but with a high load current. The motor windings will overheat quickly, and under normal circumstances the compressor will be protected by a thermal switch. When the motor windings cool down to the set temperature, the contactor closes, but the compressor fails to start and experiences stall, entering a dead loop of \"stall – thermal protection – stall\". If a phase loss occurs during compressor startup, the compressor will fail to start and experience stall, entering a vicious cycle of \"stall – thermal protection – stall\". The percentage calculation method for voltage imbalance is the ratio of the maximum deviation of the phase voltage from the average value of the three-phase voltages to that average value. As a result of voltage imbalance, the imbalance in load current during normal operation is 4 to 10 times the percentage of voltage imbalance. 　　4. Insufficient cooling of the compressor motor A large amount of refrigerant leakage or a low evaporation pressure can result in a decrease in the system’s mass flow, preventing the motor from being properly cooled; overheating of the motor then leads to frequent protection failures. IX. The main cause of compressor surge damage – backflow. Backflow can easily lead to surge accidents. Even if liquid hammer is not induced, the return flow in the high-pressure chamber will dilute or wash away the lubricating oil on the sliding surface, exacerbating wear. The return flow in the low-pressure chamber structure dilutes the lubricating oil in the oil sump. Lubricating oils containing large amounts of liquid refrigerant have low viscosity, and cannot form a sufficient oil film on the friction surfaces, resulting in rapid wear of the moving parts. Furthermore, the refrigerant in the lubricating oil boils when exposed to heat during transportation, which affects the proper delivery of the lubricating oil. The further away from the oil pump, the more apparent and severe the problem becomes. If the bearings at the motor end suffer severe wear, the crankshaft may sink to one side, which can easily lead to the stator rubbing against the casing and the motor burning out. 　　For refrigeration systems where liquid return is difficult to avoid, installing a gas-liquid separator and using evacuation shutdown control can effectively prevent or reduce the hazards caused by liquid return. X. The main cause of compressor liquid hammer damage – starting with liquid present Bubbling can be clearly observed during starting with liquid present, as visible through the oil sight glass. The fundamental reason for start-up with liquid present is the large amount of refrigerant dissolved in the lubricating oil as well as that settled at its bottom, which boils suddenly when pressure drops, causing foaming in the lubricating oil. The refrigerant that starts up with liquid enters the crankcase through \"refrigerant migration\". Due to the low vapor pressure of the refrigerant in the lubricating oil, it absorbs the refrigerant vapor on the oil surface, resulting in a pressure level in the oil reservoir that is lower than that in the evaporator. The lower the oil temperature, the lower the steam pressure, and the greater the absorption capacity for refrigerant vapor. The steam in the system will gradually \"migrate\" toward the compressor. The longer the downtime, the more refrigerant will migrate into the lubricating oil. Refrigerant migration dilutes the lubricating oil. It can also easily cause liquid slugging in the low-pressure chamber. Liquid refrigerants or mixtures of oil and refrigerant are not good lubricants; they can cause wear or even jamming. At this time, since the motor is submerged in liquid, the overload protector on the motor will not activate. Installing a crankcase heater, a gas-liquid separator, and using evacuation shutdown control can effectively prevent or reduce refrigerant migration. XI. The main cause of compressor surge damage – excessive lubricating oil. In compressors with a low-pressure chamber, the rapidly rotating components such as the rotor frequently strike the oil surface; if the oil level is too high, this leads to significant splashing of lubricating oil. If the splashing lubricating oil enters the intake tract and then reaches the cylinder, it can cause liquid slugging. XII. Main causes of high-temperature damage to compressors Overheating issues such as high motor temperature, excessive exhaust temperature, and burning of lubricating oil, which are caused by problems like misuse beyond specified limits, abnormal power supply, motor overload, refrigerant leakage, and excessively high condensing pressure. The surface temperature of the compressor is one of the important indicators to determine whether the compressor is overheating. If the surface temperature exceeds 135°C, it is generally considered that the compressor is in a severe overheating condition ； And if the surface temperature is below 120°C, the compressor temperature is normal. The motor generates a lot of heat; abnormal power supply can lead to increased heating in the motor. Issues such as unstable voltage, voltage that is too low or too high, voltage imbalance, and lack of phase balance all fall under the category of abnormal power supply conditions. 　　Problems such as frequent compressor startups, rod seizure, piston scuffing, insufficient lubrication, or lack of oil can all **increase heat generation. Using the compressor beyond its specified range can easily cause the motor to overheat and get damaged, as well as lead to insufficient cooling of the motor. The low evaporation temperature and low mass flow rate of the refrigerant result in insufficient cooling of the motor. When the amount of refrigerant leakage is high, the mass flow rate of the refrigerant also decreases, resulting in insufficient cooling of the motor. 13. Main reasons for excessively high exhaust temperature The main causes of high exhaust temperature include the following: high return air temperature, high heating capacity of the motor, high compression ratio, high condensing pressure, and improper selection of refrigerant. As a refrigeration chain service platform in China, Jiuqi Refrigeration has been focusing on the refrigeration industry. It has risen rapidly in the industry thanks to its expertise and advanced technologies in the field of refrigeration. I hope to work together with all stakeholders in the industry to contribute to the development of China’s cold storage sector. 24/7 cloud cold chain service provider – service at your doorstep! Jiui Refrigeration – China’s refrigeration chain service platform, the provider of services for the last mile!