Maintenance and Failure Analysis of Screw Refrigeration Compressor
1. Abnormal compression ratio:
The compression ratio is no stranger to those who know the performance of the compressor. The difference between the screw machine and the piston machine is that the piston machine will only be under-compressed, while the screw machine will be over-compressed.
Screw compressor compression ratio is too large: the system may deviate from the design value, the main phenomena are that the exhaust pressure temperature is too high, the suction pressure is low, and the temperature is high.
Screw compressor compression ratio is too small: the main effect is the wet stroke. In fact, the screw compressor is more afraid of the wet stroke. If a large amount of liquid returns to the compressor, it will cause the dilution of the lubricating oil. The consequence is equivalent to the high exhaust temperature.
2. Low condenser efficiency:
Low condenser efficiency: Mainly affect the supply temperature and whether the liquid can be formed. The condensation effect is too good, such as low ring temperature, too good condensation effect, resulting in higher efficiency of liquid entering the evaporator, low suction superheat, and low expansion valve sensitivity, which will cause liquid shock when starting up.
3. Low or high evaporator efficiency:
Low efficiency of the evaporator: the main effect is the cooling of the cooled object, while the wet stroke of the compressor is affected. And high efficiency will cause the suction superheat to be too large, which will affect the compressor discharge temperature. The wet stroke can be judged according to the pressure enthalpy diagram, or the value of the exhaust gas temperature minus the temperature after condensation.
4. Oil circuit problem:
Oil circuit: Mainly reflected in the oil quality, cleanliness, oil return temperature, etc. The main role of lubricating oil in the screw compressor refrigeration system is lubrication, cooling and sealing. The oil return temperature greatly affects the service life of the screw compressor. Generally, the recommended operating temperature is between 40 and 60°C, and some manufacturers also mark 70°C or 80°C. Excessive oil temperature will cause the coking of the oil and destroy the formation of the oil film. The oil temperature also affects the exhaust temperature, which in turn affects the compression ratio.
5. The oil boils during startup or operation:
Oil boiling during machine or operation: This fault belongs to the compressor fluid intake, or there is too much refrigerant in the lubricating oil, please adjust the throttling mechanism to check whether the refrigerant is overcharged.
6, the oil level is insufficient or too high:
Insufficient oil level: It should be considered whether it is a fault in the oil, the amount of oil is insufficient, and it is difficult to return the oil to the evaporator. When repairing, pay attention to whether the reservoir has no liquid level, and consider the failure of the throttling 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.
7. Exhaust temperature is too high:
High exhaust temperature: There are many factors, mainly considering too much or too little refrigerant, too high suction overheating, unstable working conditions, etc.
8. The suction pressure is low or fluctuates:
The suction pressure is low: the main reason is the lack of refrigerant, the imbalance of the throttling mechanism, the high condensing temperature, liquid hammer, etc.
