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A compressor is a fluid machine that raises low-pressure gas to high-pressure gas Home air conditioning is not cooling, still looking for someone to repair at a high price Here teach you how to repair! Identify the failure of a fully enclosed refrigeration compressor in three minutes Judgment and common sense of fluoride deficiency in central air conditioning Precautions for the use of central air conditioner thermostatScrew refrigeration compressors are prone to these types of failures, have you ever encountered them
1. Fault type
1. Abnormal compression ratio
2. Low condenser efficiency and failure
3. Low evaporator efficiency and failure
4. Failure of the oil system
5.Electrical failure
6.Second, fault analysis
Abnormal compression ratio
Compression ratio is no stranger to those who know the performance of the compressor. But what's the use of compression ratio? Is it just a calculation tool designed, but it is not.
The difference between the screw machine and the piston machine is that the piston machine will only under-compress, while the screw machine will over-compress.
Affected by the structure, the screw machine has an important data, that is, the volume ratio, the English abbreviation Vi, Vi is fixed for most screw compressors. From the point of view of maintenance operation, the value of its internal volume ratio is very similar to the value of the external compression ratio (the absolute pressure ratio of condensing pressure to evaporating pressure). This compressor has the highest efficiency.
So what happens when the compression ratio is large or small?
Too large, or too large pressure difference, proves that this system completely deviates from the design value, the main phenomenon is that the temperature of the exhaust temperature is too high, the suction pressure is too low, and the temperature is too high.
If the exhaust pressure temperature is too high, the adverse consequences are mainly due to the fact that the lubricating oil in the system is susceptible to coking, it is not suitable to form an oil film, and the rotor cannot be sufficiently lubricated. If the rotor is not effectively cooled, the rotor will be blocked and the motor will be damaged.
Low suction pressure, high suction pressure temperature mainly affects motor cooling, and high exhaust temperature. The consequences are basically equivalent to high exhaust temperature and pressure.
If it is too small, the main impact is the wet stroke (flushes, frost), in some materials, the screw compressor is resistant to wet strokes, including some of our designs, and the sales staff also love this promotion. In fact, the screw machine is more afraid of wet strokes. If a large amount of liquid returns to the compressor, it will cause the dilution of the lubricating oil, and the consequence is equivalent to a high exhaust temperature.
Of course, the compression ratio is too small, and there is also a serious rotor wear, which is caused by the increase and decrease of load failure.
2. Low condenser efficiency
The low efficiency of the condenser mainly affects the temperature of the liquid supply and whether liquid can be formed. We know that the expansion valve is ideally supplied with full liquid. In this case, the efficiency of the system is higher and the cooling capacity is the largest. Moreover, large-scale units basically have additional storage, mainly used in oil cooling. Therefore, maintaining the high efficiency of the condenser is particularly important. The fault is mainly caused by the wrong type of cooling mode, insufficient evaporation area, insufficient cooling medium, and insufficient heat exchange. Therefore, the key to check the fan, water pump, fins, etc
7.Speaking of which, the condensation effect is too good, for example, the ring temperature is too low, the condensation effect is too good, which causes the liquid to enter the evaporator more efficiently. At this time, the suction superheat is very low, and the expansion valve sensitivity is low, which will Turn on the hydraulic blow. Or the difference between the discharge pressure and the suction pressure is insufficient, which is fatal to the screw machine with differential pressure oil supply.
Low or high evaporator efficiency
The low efficiency of the evaporator mainly affects the cooling of the object to be cooled, and the wet stroke affects the compressor. The high efficiency will cause the suction superheat to be too large, which will affect the compressor discharge temperature.
Judgment of wet stroke
Wet stroke, under low temperature conditions, the judgment is actually relatively simple, mainly by the compressor suction frost line to judge, but what about the air conditioner? Rely on dew? Especially for chillers, problems in judgment will cause problems such as rupture and water ingress. Therefore, it can be judged according to the pressure enthalpy diagram, or the value of the exhaust gas temperature minus the temperature after condensation. If this value is less than 30K, it can be judged as the wet stroke.
Let me say one more thing, expansion valves, I don't have a single column (see the Zuo Zuo expansion valve maintenance). The expansion valve is not a universal adjustment valve, and not all working conditions are in line with the expansion valve adjustment requirements. Especially the big horse cart.
Oil road problem
The oil circuit is mainly reflected in the quality, cleanliness and oil return temperature of the oil. The main functions of the lubricating oil in the refrigeration system of the screw compressor are lubrication, cooling and sealing.
In addition, it also has the effect of noise reduction and shock absorption, but the industry has a relatively large controversy. The main reason is that oil will form gas bubbles in the motor part. The gas bubbles will eliminate the noise, but some manufacturers think it is useless, and the gas liquid is difficult Control, so instead of adding foam inhibitor.
Shock absorption is mainly for the lubrication of rolling bearings, this effect is not obvious, so the above two functions can not be regarded as the main function.
The temperature of the oil return affects the service life of the screw compressor to a great extent. The recommended operating temperature is generally between 40 and 60 ℃, and some manufacturers have also marked 70 ℃ or 80 ℃. Excessively high oil temperature will cause oil coking and destroy the formation of oil film. The oil temperature also affects the exhaust temperature and thus the compression ratio, so please pay attention to adjust when selecting the oil temperature.
Cleanliness of oil
The cleanliness of the oil is also the cleanliness of the system. Maintaining cleanliness is the main feature of the screw machine. The screw compressor is not equivalent to the piston compressor. Due to structural reasons, the cleanliness of the system is higher than that of the piston machine. Due to the relatively high speed of the meshing rotor, some foreign objects will be quickly drawn into the compressor, causing damage to the meshing rotor, especially some small particles of metal or foreign objects, which will break the interception of the suction filter (including some relatively large foreign objects, There are also a few damages to the filter screen due to the suction.) Even the assembly problem of the machine itself causes the parts to fall off and get stuck between the rotors. It will inevitably cause direct damage to the motor. Although the small metal particles do not directly act, they impact the rotor oil film, causing poor lubrication of the rotor bearings. Clamping and biting the bearing box are also common. The most terrifying thing is that the small particles will form short-circuit chains and directly cause damage to the motor.
Acidic lubricant compressors often smell the scorched smell of lubricating oil during start-up analysis. When the metal surface is severely worn, the temperature is very high, and the lubricating oil starts to scorch when it is above 175oC. If there is more water in the system (the vacuum is not ideal, the lubricating oil and refrigerant have a large water content, and the air enters after the negative pressure return air pipe ruptures), the lubricating oil may appear acidic. Acid lubricating oil will corrode the copper tube and the winding insulation layer. On the one hand, it will cause copper plating. On the other hand, the acidic lubricating oil containing copper atoms has poor insulation performance and provides conditions for winding short circuit.
3. Other failures
For screw compressors, many types of faults are entangled in several aspects, such as lubrication failure caused by oil shortage, bearing jamming, rotor jamming, and then compressor motor stalls, the compressor meets abnormally high, motor burn. And why is there a lack of oil or lubrication failure? In fact, it is mostly caused by the exhaust gas temperature being too high and liquid blow. Therefore, for maintenance personnel, these require careful observation and diligent thinking before they can be repaired.
1. Oil boiling during startup or operation
This fault belongs to compressor liquid intake, or there is too much refrigerant in the lubricating oil. Please adjust the throttle mechanism to check whether the refrigerant is overcharged.
2. The oil level is insufficient or too high
If it is insufficient, it should be considered whether it is an oil fault, insufficient fuel supply, and difficulty in returning oil to the evaporator. Pay attention to whether there is no liquid level in the reservoir during maintenance, and consider the failure of the throttle mechanism or the unreasonable installation.
If it is too high, it should be considered that the oil filter is blocked, and the refrigerant is mixed into the oil.
3. The exhaust temperature is too high
There are many factors of high exhaust temperature, mainly considering too much or too little refrigerant, too high intake heat, unstable operating conditions, etc.
4. Inspiratory pressure is low or fluctuating
The low suction pressure is mainly due to the lack of refrigerant, the adjustment of the throttle mechanism, the high condensation temperature, and the liquid blow.
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