Working principle of screw air compressor
The compressed air system uses a twin-screw air compressor. The work of the machine is divided into three processes: intake, compression and exhaust:
1. Inhalation process:
The motor drives the rotor. When the red groove space of the master and slave rotors turns to the opening of the air intake end wall, the space is large and the outside air is filled in it. The air in the groove is sealed between the main and slave rotors and the casing to complete the suction process. When the gas fills the entire tooth groove, the end surface of the rotor inlet side turns away from the air inlet of the casing, and the gas in the tooth groove is absorbed seal.
2. Compression process:
At the end of the suction, the main and slave rotor tooth crests are closed with the casing. At this time, the gas no longer flows out in the tooth grooves, and its tooth meshing surface gradually moves to the exhaust end. The tooth groove space between the tooth surface and the exhaust port gradually becomes smaller, and the gas in the tooth groove is compressed and the pressure is increased.
3. Exhaust process:
When the toothed end surface of the rotor turns to communicate with the exhaust port of the casing, the compressed gas starts to be discharged.
Several common faults of screw air compressors
1. When the screw air compressor is stopped, the air inlet of the screw air compressor sprays oil outward. When the air compressor stops suddenly and does not open the exhaust valve in time to discharge exhaust gas, the air inlet sprays cooling oil outward. At this moment, you should first check whether the air inlet valve is faulty and cannot be closed normally. No fault, if it is normal, you should further check whether the check valve on the main exhaust pipe is closed in time or whether it is completely closed, and if there is a fault, it should be ruled out.
2. The screw air compressor automatically stops during work. There are two main reasons why the machine automatically trips and shuts down during work: (1) It is a factor of the power supply grid. Because the machine itself has safety protection devices such as undervoltage protector, wrong phase protector, and high voltage protector. When the grid voltage is about 90% lower than the rated voltage (380V), or the phase sequence of the power supply is incorrect or the phase of the three-phase power supply is missing, it will automatically trip and stop. (2) The exhaust temperature is too high. It may be that the lubricating oil is lacking, the cooler is blocked, or the temperature control valve is malfunctioning and cannot operate normally.
3. The temperature is too high. The maximum exhaust temperature of the screw air compressor is set at 120 degrees Celsius. When the temperature reaches 110 degrees, the temperature warning light starts to flash and alarm, and when it exceeds 120 degrees, it will automatically stop. There are usually the following reasons for the shutdown of the machine when the temperature is too high:
(1) The environmental ventilation and heat dissipation are poor. The surrounding environment of the screw air compressor affects the heat dissipation mainly in three situations: first, it is too close to obstacles such as walls; second, there are other heat sources near the screw air compressor; Form a strong air current.
(2) The fan blades of the screw air compressor are cracked or loose. When the fan blade is cracked, the air compressor will automatically shut down due to the high temperature after working for about 5 minutes, and it will make abnormal noise. If the fan blade is broken, the cooling air volume will decrease and affect the heat dissipation. At this time, the fan blade should be replaced or adjusted.
(3) The oil filter of the screw air compressor is too dirty. When it is too dirty, the resistance oil cannot enter the air compressor according to the normal flow rate, and the air compressor will heat up rapidly due to the lack of cooling lubricating oil. When the oil pressure difference between inlet and outlet exceeds 0.18MPa, the filter element needs to be replaced.
(4) The cooling oil level is too low. When the cold machine is checked, the oil level should be compensated immediately when it is lower than the lower end of the inspection tube. During the working process, the position below the center of the oil mark should be compensated.
(5) The cooling oil number is low or the oil quality is poor. The screw air compressor uses the manufacturer’s special air compressor oil. When other low-grade or inferior oil is used, the viscosity and specific heat will not meet the standard, resulting in excessive temperature.
(6) The radiator is blocked. When the environment around the screw air compressor is dusty, long-term work will form a layer of dust or sludge on the surface of the radiator, and the internal copper pipes will be easily blocked by the accumulation of grease, which will affect the heat dissipation effect. For the air cooler, clean the outside with a dust gun. If it is not clean, clean it with a high-pressure water gun after removing it, and clean the inside with a special potion. If it is a water cooler, then use a water pump to circulate the liquid medicine to clean it.
(7) The oil cut-off valve of the screw air compressor fails. There is an oil cut-off valve between the oil filter and the air compressor. When the oil cut-off valve cannot be opened, due to no oil lubrication and cooling, the temperature of the screw air compressor rises rapidly after starting, and it will automatically stop in about a few seconds.
(8) The filter element of the oil-gas separator is too dirty. When it is too dirty, the oil will affect the circulation due to excessive resistance, resulting in an overheating shutdown, and it should be cleaned or replaced.
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