Screw refrigeration compressors are prone to these types of failures, have you encountered them? The compressor is a volumetric compressor.Since its use in 1934, it has a dominant position in small to large and medium-sized refrigeration systems because of its excellent performance, not suitable for wear, and large unit cooling capacity. Then the screw compressor for fluorine refrigeration is used. What types of failures are prone to occur, let us take a closer look! First, the type of failure 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 Second, fault analysis 1. Abnormal compression ratio Compression ratio is not unfamiliar to those who know the performance of the compressor. But what is the use of compression ratio? Is it just a design calculation tool, it is not. The difference between a screw machine and a piston machine is that the piston machine will only under-compress, and the screw machine will over-compress. Affected by the structure, the screw machine has an important data, that is, the content volume ratio, the English abbreviation Vi, Vi is fixed for most screw compressors. From the perspective of maintenance operation, the value of the content volume ratio is externally compressed. The value of the ratio (the absolute pressure ratio of condensing pressure and evaporating pressure) is very similar, and this compressor has the highest efficiency. So what happens when the compression ratio is large or small? is too large, or the pressure difference is too large, which 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 low, and the temperature is high. The exhaust pressure temperature is too high, and the undesirable consequences are mainly due to the fact that the lubricating oil in the system is easy to coke, it is not suitable to form an oil film, and the rotor cannot be sufficiently lubricated.The rotor cannot be effectively cooled down.If it is lubricated, it will block and cause the motor to 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 effect is the wet stroke (tide car, 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, screw machines are 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 relatively small, and there are serious rotor wear and tear caused by load and failure.
2. Low condenser efficiency The low efficiency of the condenser mainly affects the temperature of the liquid supply and whether it can form a liquid. We know that the expansion valve is ideally a full liquid supply. In this case, the efficiency of the system is higher and the cooling capacity is the largest. Moreover, it is basically available on large units. Attached storage is mainly used for oil cooling. Therefore, it is particularly important to maintain the high efficiency of the condenser. Its failure is mainly caused by the incorrect selection of cooling method, insufficient evaporation area, insufficient cooling medium, and insufficient heat exchange, so it is mainly checked during inspection Fans, pumps, fins and other key. Speaking of which, the condensation effect is too good, for example, the ring temperature is too low, and 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 cause Start-up fluid blow. Or the difference between the exhaust pressure and the suction pressure is insufficient, which is fatal to the screw machine with differential pressure oil supply. 3. Evaporator efficiency is low or high The low efficiency of the evaporator mainly affects the cooling of the object to be cooled, and the wet stroke of the compressor. The high efficiency will also cause the intake 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 through the compressor suction frost line to judge, but what about the air conditioner? Dew? Especially for the chiller, if there is a problem in the judgment, it will cause a shutdown Problems such as rupture and water inflow. Therefore, it can be judged according to the pressure enthalpy diagram, or the value of the exhaust temperature minus the temperature after condensation, which is less than 30K, which can be judged as a wet stroke. I would like to say one more thing here, the expansion valve, I do not have a single row (see the Zuo Zuo expansion valve maintenance). The expansion valve is not a universal adjustment valve, not all working conditions are in line with the expansion valve adjustment requirements. Especially the big horse cart. 4. Oil road problem The oil circuit is mainly reflected in the quality, cleanliness, oil return temperature and other lubricants in the screw compressor refrigeration system.The main functions are lubrication, cooling, and sealing. In addition, it also has the effect of noise removal and shock absorption, but the industry is more controversial, mainly because the oil will form gas bubbles in the motor part, and 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. Vibration damping is mainly for the lubrication of rolling bearings, this effect is not obvious, so the above two functions cannot be counted as main functions. The temperature of the oil return affects the service life of the screw compressor to a large extent. The recommended operating temperature is generally between 40 and 60°C, and some manufacturers also label 70°C or 80°C. Excessively high oil temperature will cause oil Coking, destroying the formation of oil film, the oil temperature also affects the exhaust temperature, which in turn affects the compression ratio, so please pay attention to adjust when choosing 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 meshing The speed of the rotor is quite high, some foreign objects will be sucked into the compressor very quickly, 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 larger foreign objects, due to suction There is also a small number of filter damages caused by gas), or even the assembly problem of the machine itself, causing parts to fall off and get stuck between the rotors. It is bound to cause direct damage to the motor. Although the small metal particles do not directly act, but they impact the rotor oil film, It is also common to cause poor lubrication of rotor bearings, jamming cylinders and biting bearing boxes.The most frightening thing is that 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. The temperature is very high when the metal surface is severely worn, and the lubricating oil starts to coke when it is above 175oC. If there is more moisture in the system ( The vacuum is not ideal, the water content of the lubricating oil and refrigerant is large, and the air enters after the negative pressure return pipe is broken.), the lubricating oil may appear acidic. The acidic lubricating oil will corrode the copper pipe and the winding insulation layer. On the one hand, it will Causes copper plating; on the other hand, this kind of acid lubricant containing copper atoms has poor insulation performance and provides conditions for winding short circuits. 3. Other failures For screw compressor units, many types of faults are entangled in several aspects, such as lubrication failure caused by oil shortage, which causes the bearing to be stuck and the rotor to be stuck. Burned. And why is there a lack of oil or lubrication failure? In fact, it is more caused by the high exhaust temperature and liquid strike. Therefore, for maintenance personnel, these need to be carefully observed, diligently thought, before they can Maintenance is perfect. 1. Oil boiling during startup or operation This fault belongs to the compressor liquid intake, or the refrigerant in the lubricating oil is too much, please adjust the throttle mechanism to check whether the refrigerant is overcharged. 2. The oil level is insufficient or too high Insufficiency should be considered whether it is an oil content failure, insufficient fuel supply, and difficulty in returning oil to the evaporator. When repairing, pay attention to whether the reservoir has no liquid level, and should consider the failure of the throttle mechanism or unreasonable installation. Too high should consider the oil filter plugging, refrigerant mixed into the oil. 3. The exhaust temperature is too high There are many high exhaust temperature factors, mainly considering too much or too little refrigerant, too high intake heat, unstable working conditions, etc. 4. Inspiratory pressure is low or fluctuating
